Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acs.jpcb.2c04109

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acs.jpclett.2c01839

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Layered hybrid organic-inorganic halide perovskites have emerged as durable and tunable candidates for optoelectronic materials due to their outstanding properties. Here, we report the temperature-induced structural transition and photophysical properties of the layered perovskite (MA)(2)PbI2-xBrx(SCN)(2) (MA = CH3NH3; 0 <= x <= 1.2). Synchrotron X-ray diffraction measurements demonstrate that there is a first-order structural phase transition with an increase of the interlayer distance in (MA)(2)PbI2(SCN)(2) (x = 0) at 315 K. We attribute this transition to order-disorder transformations of the molecular ions, MA(+) and SCN-. The observed transition temperature decreases with Br substitution (from 320 K to 270 K), suggesting a weakening of bonding interaction between the molecular ions. A decrease in the decomposition temperature was also observed by Br substitution, indicating that the strength of interlayer bonding is coupled with the thermal stability of the layered perovskite. Photocurrent transient measurements for (MA)(2)PbI2(SCN)(2) reveal a dramatic decrease of the fast decay component upon heating, indicating that the structural transition decreases the carriers in the crystalline domain by random distortion of the perovskite layer derived from disordering of molecular ions. This study provides insight into the structure and photophysical properties of the thiocyanate layered perovskite family.

DOI： 10.1039/d2ce00733a

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Publisher：American Chemical Society (ACS)  

Luminescent radicals are an emerging class of materials that exhibit unique photofunctions not found in closed-shell molecules due to their open-shell electronic structure. Particularly promising are photofunctions in which radical’s spin and luminescence are correlated; for example, when a magnetic field can affect luminescence (i.e., magnetoluminescence, ML). These photofunctions could be useful in the new science of spin photonics. However, previous observations of ML in radicals have been limited to systems in which radicals are randomly doped in host crystals or polymerized through metal complexation. This study shows that a covalently linked luminescent radical dimer (diradical) can exhibit the ML as a single-molecular property. This facilitates detailed elucidation of the requirements for and mechanisms of ML in radicals and can aid the rational design of ML-active radicals based on synthetic chemistry.

DOI： 10.26434/chemrxiv-2022-1wscq

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DOI： 10.1021/acs.langmuir.2c00290

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Language：English   Publishing type：Research paper (scientific journal)  

The synthesis, excited state dynamics, and substituent effect on the 1O2-generation efficiency of several copper(II) complexes of 5,15-diazaporphyrin (CuDAPs) bearing peripheral substituents are reported. 10,20-Diaryl-CuDAPs were prepared via a new method consisting of metal-templated cyclization and N-dealkylation as key steps. The effect of the β-substituents on the optical and redox properties of CuDAP was stronger than that of the meso-aryl groups, which can be explained by considering the characteristics of the HOMO and LUMO of the DAP ring. The excited state dynamics and 1O2-generation efficiency of CuDAPs were studied using time-resolved spectroscopic techniques; the electronic effect of the meso-aryl groups on the triplet lifetime and 1O2-generation quantum yield was relatively weak, whereas that of the β-(1-pyrazolyl) groups was appreciable. The analysis of the temperature dependence of phosphorescence spectra of 10,20-bis(2,4,6-trimethylphenyl)-CuDAP allowed the energy gap between the excited trip-quartet and trip-doublet states to be determined. The relatively long triplet lifetimes of CuDAPs show their potential for future application as photosensitizers.

DOI： 10.1246/bcsj.20220002

Scopus

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Herein, we report a series of 9-(diphenylphosphoryl)-10-(phenylethynyl)anthracenes (DPPPEAs) as novel fluorescent 9,10-disubstituted anthracene derivatives. The DPPPEAs were prepared by Sonogashira coupling of (10-bromoanthracen-9-yl)diphenylphosphine oxide with terminal arylacetylenes, and their structures were fully characterized. UV/Vis fluorescence spectroscopy and theoretical calculations were used to evaluate substituent effects on fluorescence properties of DPPPEAs. The nature of emissive excited state of DPPPEAs was found to vary greatly depending on the substituent, solvent, and temperature. Unsubstituted DPPPEA emitted intense fluorescence from locally excited (LE) state, whereas donor-acceptor (D-A) type DPPPEAs substituted with diphenylamino groups showed strong solvatofluorochromism derived from the charge-transfer (CT) state. Notably, carbazolyl derivatives exhibited fluorescence from LE hybridized with CT state. The disappearance of CT emission in rigid media suggests that solvent reorganization plays a crucial role in producing large Stokes shifts of D-A type derivatives. The DPPPEAs have also been found to function as annihilators in porphyrin-sensitized triplet–triplet annihilation processes.

DOI： 10.1002/cptc.202200100

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DOI： 10.1021/acs.jpcc.1c07807

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Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

Since the photocharge generation efficiency has reached nearly 100% for recent organic photovoltaic film materials, clarification of loss mechanisms becomes of increasing importance. Here, we report a new time-resolved measurement method that enables simultaneous detection of the optical absorption and electric current due to photogenerated carriers in organic semiconductor films. Microsecond-order decays of both the number density (recombination) and the averaged drift mobility (trapping) of photocarriers are quantitatively observed for an identical device of a regioregular poly[3-hexylthiophene-2,5-diyl]:(6,6)-phenyl C-61 butyric acid methyl ester bulk heterojunction film. The decay feature of the time-dependent mobility is highly dispersive especially at lower temperatures. It can be explained by fast thermalization of "hot" photocarriers into lower energy sites, which is followed by thermally activated hopping. This quantitative time-resolved observation method can be a powerful tool for characterization and optimization of photovoltaic materials.

DOI： 10.1021/acs.jpcc.1c06879

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

This work reports a series of covalently linked hybrids comprising 5,10,15,20-tetraaryl-5,15-diazaporphyrinoids (M-TADAP; M = Ni, Zn, Cu) and amines. M-TADAP-amine hybrids were prepared via the metal-templated cyclization of the corresponding metal(II)-dipyrrin complexes and redox reactions on the DAP unit. In the UV/vis/near-IR absorption spectra of the hybrids containing an 18 pi-electron DAP ring, broad charge-transfer bands were observed, reflecting the electron-donating property of the para-aminophenyl groups and the electron-accepting property of the 18 pi TADAP dication. The electrochemical behavior of the M-TADAP-amine hybrids was strongly dependent on the structure of the peripheral amine units. Further electrochemical oxidation of the hybrids bearing N-Ph groups conceivably generated amine-centered radicals, which sequentially underwent irreversible coupling to form benzidine-linked M-TADAP polymer films. The Ni-TADAP-benzidine polymer exhibited the electric conductivity of 2x10(-3) S m(-1).

DOI： 10.1002/cplu.202100429

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Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/cplu.202100429

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1,3,2,4-Diazadiboretidine, an isoelectronic heteroanalogue of cyclobutadiene, is an interesting chemical species in terms of comparison with the carbon system, whereas its properties have never been investigated experimentally. According to Baird's rule, Huckel antiaromatic cyclobutadiene acquires aromaticity in the lowest triplet state. Here we report experimental and theoretical studies on the ground- and excited-state antiaromaticity/aromaticity as well as the photophysical properties of an isolable 1,3,2,4-diazadiboretidine derivative. The crystal structure of the diazadiboretidine derivative revealed that the B2N2 ring adopts a planar rhombic geometry in the ground state. Yet, theoretical calculations showed that the B2N2 ring turns to a square geometry with a nonaromatic character in the lowest triplet state. Notably, the diazadiboretidine derivative has the lowest singlet and triplet states lying at close energy levels and displays blue phosphorescence.

DOI： 10.1002/anie.202106490

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

DOI： 10.1002/ange.202108413

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Electron-transfer (ET) reactions in biological systems, such as those with magnetic sensors based on flavoproteins and electron transport at biomembrane interfaces, are interesting and important issues that require understanding. As a model system of flavoproteins in biomimetic environments, we report the dynamics of the radical pair generated by photoinduced ET between riboflavin tetrabutylate (RFTB) and tryptophan (Trp) residues in a transmembrane-type polypeptide, both of which are distributed in a large unilamellar vesicle of 1,2-dimyristoyl-sn-glycero-3-phosphocholine. The Trp residues locate near the hydrophilic membrane interface, as confirmed by a dual-fluorescence quenching assay. The fluorescence and transient absorption upon photoexcitation of RFTB indicate that ET from both the singlet and triplet excited states occurs at the hydrophilic interface, whereas the RFTB in the hydrophobic region does not contribute to ET. The ET efficiency and the magnetic field effect (MFE) on the RFTB anion increase significantly above the gel-to-liquid crystal phase transition temperature due to a decrease in microviscosity. The MFE analysis indicates that the radical pair generated from the triplet ET channel exhibits a long lifetime as those in micellar systems due to the strong cage effect of the vesicle.

DOI： 10.1021/acs.jpcb.1c01231

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acs.jpcc.0c04904

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

A debrominative oxygenation protocol has been developed for the conversion of α-bromo-α,α-dialkyl-substituted carbonyl compounds to their corresponding α-hydroxy analogues. For example, stirring a solution of α-bromoisobutyrophenone and 2-aryl-1,3-dimethylbenzimidazoline (BIH-Ar) at room temperature under an air atmosphere leads to the efficient formation of α-hydroperoxyisobutyrophenone, which can be converted to α-hydroxyisobutyrophenone using Me2S reduction. In contrast, reaction of α-bromoacetophenone under the same conditions produces the α-hydrogenated product acetophenone. α-Keto-alkyl and benzimidazolyl radicals (BI•-Ar), generated via dissociative electron transfer from BIH-Ar to α-bromoketone substrates, serve as key intermediates in the oxidation and reduction processes. The dramatic switch from hydrogenation to oxygenation is attributed to a steric effect of α-alkyl substituents, which causes hydrogen atom abstraction from sterically crowded BIH-Ar to α-keto-alkyl radicals to be slow and enable preferential reaction with molecular oxygen. Generation of the α-keto-alkyl radical and BI•-Ar intermediates in these process and their sterically governed hydrogen atom transfer reactions are supported by results arising from DFT calculations. Moreover, an electron spin resonance study showed that visible light irradiation of phenyl benzimidazoline (BIH-Ph) in the presence of molecular oxygen produces the benzimidazolyl radical (BI•-Ph). The addition of thiophenol into the reaction of α-bromoisobutyrophenone and BIH-Ph predominantly produced α-phenylthiolated isobutyrophenone even if a high concentration of molecular oxygen exists. Furthermore, the developed protocol was applied to other α-bromo-α,α-dialkylated carbonyl compounds.

DOI： 10.1021/acsomega.0c00509

PubMed

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Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

For realization of efficient organic light-energy conversion systems, controlling the lifetime of photogenerated charge separated states in donor (D)–acceptor (A) molecules is of much importance; the spin dynamics is one of the important controlling factors. We previously reported that the covalently-linked 1,3-bis(2-pyridylimino)-isoindolate platinum (BPIPt)–dimethoxytriphenylamine (D)–naphthaldiimide (A) triad molecule (BPIPt–DA) exhibits a triplet-born long-lived charge separated state (BPIPt–D+A−), the lifetime of which is significantly increased from 4 ms to 10 ms by an applied magnetic field of 270 mT in room temperature tetrahydrofuran (THF). The purpose of the present study is to clarify detailed dynamics of spin-dependent generation and the decay of BPIPt–D+A−. For this purpose, we measured transient optical absorption (TA) and the TA-detected magnetic field effect (MFE) as functions of temperature and dispersion media. In THF at 183 K, MFE-detected transient spectra of the intermediate BPIPt−–D+A state are observed. We have successfully quantified the recombination loss at this state by a kinetic simulation of MFE without using any reference molecules. The lifetime of the final BPIPt–D+A− state in a cellulose acetate polymer matrix at room temperature is significantly prolonged to 20 ms at 0 mT and 96 ms at 250 mT compared to those in THF. From the comparison of temperature dependences of the two media, effects of molecular motions on the electronic coupling and the spin relaxation are discussed.

DOI： 10.1063/1.5127940

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Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

In order to clarify roles of higher fullerenes on the charge recombination in organic solar cells based on the bulk heterojunction (BJ) of polymers as electron donors (Ds) and fullerenes as electron acceptors (As), we measured magnetoconductance (MC) effects for the BJ-cells consisted of a blend film of regioregular poly[3-hexylthiophene] (P3HT) and [6,6]-phenyl-C-71-butyric acid methyl ester (PC71BM), hereafter referred to as C-71-cell, and compared them with the results for P3HT:PC61BM-cell (C-61-cell) reported in our previous paper. As with C-61-cell, three components (MCS,M,B) with half-field-at-half-maximums of 4 +/- 1, 28 +/- 12 and > 400 mT were detected in the magnetic field dependence of the MC effects for the C-71-cell under dark and light conditions. From the incident light power and time dependences of the positive MCS and MCM components in light, it was assinged that the light MC effects observed for the C-71-cell is attributed to geminate recombination of the electron-hole (e-h) pair, whereas the C-61-cell shows positive light MC effects due to nongeminate recombination. This is explained by decrease of the possiblity to form nongeminate e-h pair because C-71-cells have wide D/A junction caused by uniform mixing of P3HT and PC71BM more than C-61-cells. The positive low-field MC effects due to the geminate e-h pair in the C-71-cell indicates that the recombination rate constant for the (3)e-h pair (k(T)) to the triplet exciton ((3)ex) is greater than that for the (1)e-h pair (k(S)) to the singlet ground state ((1)gr). The magnitude relationship of k(S) < k(T) is opposite to that for C-61-cell. Kinetic analysis on the low-field MC effects for the C-71-cell provided that the recombination yield of the geminate e-h pair is 0.5%. The inversion of magnitude relationship for the spin-dependence in recombination rate by replacing PC61BM with PC71BM are explained by a reorganization energy of PC71BM smaller than that of PC61BM. We concluded that the recombination to the (1)gr is in the inverted regime of the Marcus theroy, but that to the (3)ex is in the normal regime, so that decrease of the reorganization energy results in drastic decrease in k(S) more than k(T).

DOI： 10.1016/j.orgel.2019.105383

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Metal complexes of 3,7,13,17-tetrakis(di(4-carboxyphenyl)amino)-5,15-diazaporphyrin (MDAP-COOH; M=Pd, Cu) and their ethyl ester precursors (MDAP-COOEt; M=Pd, Cu) have been synthesized for use as near-infrared (NIR)-light-responsive photosensitizers. Under irradiation with visible or NIR light, PdDAP-COOEt in toluene generated singlet oxygen (O-1(2)) with an excellent quantum yield (phi(Delta)=0.99), whereas CuDAP-COOEt exhibited a lower efficiency (phi(Delta)=0.21). The water-soluble Pd-II complex PdDAP-COOH also behaved as a photosensitizer (phi(Delta)=0.20) in a micellar solution. The photophysical properties of these dyes were measured by transient absorption techniques. It was found that the efficiency of the energy transfer from the triplet state of MDAP-COOR (R=Et, H) to the ground state of dioxygen was highly dependent on the peripheral substituents, the central metal, and the solvent. Furthermore, the phototoxicity of PdDAP-COOH toward HeLa cells under irradiation of NIR light (720 nm) was evaluated. As expected, PdDAP-COOH exhibited good photodynamic activity, and control experiments confirmed that O-1(2) was generated as the active oxygen species.

DOI： 10.1002/cplu.201900087

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry (RSC)  

<p>The existence of spin polarization was confirmed while spin–orbit coupling was ruled out in Fe₃O₄-based PLEDs by magneto-electroluminescence analysis.</p>

DOI： 10.1039/c9ra01501a

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For realization of low-cost organic photon-energy conversion, the supramolecular approach has been a focus of attention as a counter approach to precise synthesis of covalently linked donor (D)-acceptor (A) molecules. Here we report photogeneration of a long-lived (similar to 3 mu s) intermolecular charge-separated (CS) state of metal porphyries (D) and an alkyl viologen (A) at an interface of a vesicle membrane formed by self-assembly of nonionic surfactant and cholesterol molecules. The yield of escaped free radicals is negligibly low as in the case of CS states in covalently linked D-A systems. Furthermore, the transient concentration of the CS state dramatically increases by -100% upon application of a magnetic field of 250 mT at room temperature. The simulation of the spin dynamics of the CS state indicates that fast (similar to 10(7) s(-1)) spin-selective recombination and slow (10(5)-10(6) s(-1)) dissociation-re-encounter dynamics are the key processes for the long CS-state lifetime and the gigantic magnetic field effect. It has turned out that such dynamics are sharply dependent on temperature and alkyl chain length of the viologen. The present results would lead to the development of future materials for light energy conversion, drug delivery, and microscopic bioprobes.

DOI： 10.1021/acs.jpcb.8b08389

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

A visible light promoted process for desulfonylation of N-sulfonylamides and -amines has been developed, in which 1,3-dimethyl-2-hydroxynaphthylbenzimidazoline (HONap-BIH) serves as a light absorbing, electron and hydrogen atom donor, and a household white light-emitting diode serves as a light source. The process transforms various N-sulfonylamide and -amine substrates to desulfonylated products in moderate to excellent yields. The observation that the fluorescence of 1-methyl-2-naphthoxy anion is efficiently quenched by the substrates suggests that the mechanism for the photoinduced desulfonylation reaction begins with photoexcitation of the naphthoxide chromophore in HONap-BIH, which generates an excited species via intramolecular proton transfer between the HONap and BIH moieties. This process triggers single electron transfer to the substrate, which promotes loss of the sulfonyl group to form the free amide or amine. The results of studies employing radical probe substrates as well as DFT calculations suggest that selective nitrogen-sulfur bond cleavage of the substrate radical anion generates either a pair of an amide or amine anion and a sulfonyl radical or that of an amidyl or aminyl radical and sulfinate anion, depending on the nature of the N-substituent on the substrate. An intermolecular version of this protocol, in which 1-methyl-2-naphthol and 1,3-dimethyl-2-phenylbenzimidazoline are used concomitantly, was also examined.

DOI： 10.1021/acs.joc.8b01536

PubMed

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The magnetoconductance (MC) effect was investigated for two types of organic solar cells with single junction (SJ) and bulk junction (BJ) of poly(3-hexylthiophene) (P3HT) as donor (D) and [6,6]-phenyl-C-61-butyric acid methyl ester (PCBM) as acceptor (A). Three components with different half-field-at-half-maximums (B-1/2) of 4 +/- 1, 20 +/- 15 and >400 mT, hereafter referred to MCS,M,B in a sequence, were observed in the magnetic field dependence of the MC effects measured under dark and light conditions. The magnitude of the MCS,M,B components is sensitive to not only the junction structure of the cell but also the presence or absence of incident light. The bias voltage (17) dependence of the MC effect in the dark for the SJ-cell is maximized around the turn-on voltage (V-ON) of the dark current, where a flat band condition of the active layer is achieved. The B-1/2 for the MCM component of the SJ-cell increases with V beyond V-ON. In light, the BJ-cell exhibits the MC effect, whereas no effect is detected for the SJ-cell. The MCS,M components for the BJ-cell in light increase with the incident light power. The transient MCS,M components for the BJ-cell measured using a nanosecond pulse laser increases with the delay time after the flash. By integrating these phenomena and the phase of the MC effect, it is concluded that all of the MC components arise from the magnetic field effect on the spin conversion of nongeminate electron (e)-hole (h) pairs with spin-dependent charge recombinations at the D/A-interface. The B-1/2 values for MCS,M,B are, respectively, understood by the spin conversion due to the hyperfine interaction, the spin relaxation, and the g-factor difference for e (PCBM-) and h (P3HT(+)). Kinetic simulations of the MCS,M components for the BJ-cell observed at the short-circuit condition in light yield an efficiency of ca. 40% for the nongeminate recombination, which is accompanied by the generation of triplet excitons as well as relaxation to a ground singlet state. The loss mechanism of moderate triplet recombination suggests an important possibility to improve the power conversion efficiency by harvesting of the triplet excitons.

DOI： 10.1021/acsomega.8b01746

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/s00723-018-1035-9

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Other Link： http://link.springer.com/content/pdf/10.1007/s00723-018-1035-9.pdf

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DOI： 10.1002/solr.201700234

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

Benzimidazolium naphthoxide (-ONap-BI+) was first synthesized and utilized as an unprecedented betaine photoredox catalyst. Photoexcited state of -ONap-BI+ generated by visible light irradiation catalyzes the reductive deiodination as well as desulfonylation reactions in which 1,3-dimethyl-2-phenylbenzimidazoline (Ph-BIH) cooperates with as an electron and hydrogen atom donor. Significant solvent effects on the reaction progress were discovered, and specific solvation toward imidazolium and naphthoxide moieties of -ONap-BI+ was proposed.

DOI： 10.1021/acs.joc.8b00282

PubMed

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DOI： 10.1021/acsomega.7b00474

CiNii Article

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Dynamics of the photogeneratedcharge-separated (CS) state is studied for. a newly synthesized molecular triad, in which the donor (D) dimethoiytriphenylamine; 1,3-bis(2-pyridylimino)isoindolate platinum (BPIPt), and the acceptor (A). naphthaldiimide are linked with a triethynylbenzene unit (BPIPt-DA). Photoexcitation of BPIPt gives rise to generation, of a long lived (similar to 4 mu s) CS Tstate BPIPt-D(+)A(-), Of which the lifetime is con, Siderably increased by applied magnetic field of 270 mT.: The positive magnetic field,effect (MFE) is in contrast to the negative MFE for the reference DA molecule, which indicates successful switching of the initial spin, state of the CS state from singlet to triplet Simulations of the MFE and time resolved electron paramagnetic resonance show that spin-selective charge recombination and spin relaxation Are. Unaffected by attachment of BPIPt. The minimum impact of heavy atom substitution on the. electronic and magnetic properties-hae-been.. realized by the small electronic coupling mediated by the rigid meta-triethynylbenzene.

DOI： 10.1021/acs.jpclett.6b02887

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acs.jpca.6b02929

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The effect of the solvent viscosity dependence of time-resolved magnetoluminescence (ML) on the delayed fluorescence of 9,10-diphenylanthracene (DPA) sensitized by platinum octaethylporphyrin has clarified the structure and dynamics of the triplet triplet pair (TT), i.e., the transition state of triplet fusion. Phase inversion of the ML effect with time provides evidence for the recycle dynamics of the excited triplet state for DPA in triplet fusion. The electron spin-relaxation by random molecular rotation causes intersystem crossing among the different spin states of the triplet-triplet pair and allows the (TT)-T-3,5 to engage in triplet fusion. Therefore, slow-down of the molecular diffusion by an increase in the solvent viscosity can enhance the triplet fusion yield. However, the reduction of the ML effect observed in quite high viscosity solvents suggests that the substantially slow rotational motion decreases the triplet fusion yield due to steric factors in electron exchange from the triplet-triplet pair.

DOI： 10.1021/acs.jpcb.5b11208

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/acs.jpcc.5b10176

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

Photoinduced electron transfer (PET) reactions promoted by 2-aryl substituted 1,3-dimethylbenzimidazolines (Ar-DMBIH) were investigated. Excited states of Ar-DMBIH, formed by irradiation using light above 360 initiate PET reductions of various organic substrates, including transformations of epoxy ketones to aldols, free radical rearrangements such as the Dowd-Beckwith ring-expansion and 5-exo hexenyl cyclization, deprotection of N-sulfonyl-indols, and allylation of acyl formates. In these processes, Ar-DMBIH possessing 1-naphthyl, 2-naphthyl, 1-pyrenyl and 9-anthryl substituents formally act as two electron and one proton donors while the hydroxynaphthyl substituted derivative serves as a two electron and two proton donor. On the basis of the results of absorption spectroscopy studies, cyclic voltammetry and DFT calculation, a mechanistic sequence for these reduction reactions is proposed that involves initial photoexcitation of the aryl chromophore of the Ar-DMBIH followed by single electron transfer (SET) to the organic substrate to generate the radical cation of benzimidazoline and the radical anion of the substrate. (C) 2015 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.tet.2015.06.071

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DOI： 10.1021/acs.jpca.5b02253

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Construction of photogenerated long-lived charge-separated states is crucial for light-energy conversion using organic molecules. For realization of cheap and easy-to-make long-distance electron transfer (ET) systems, we have developed a supramolecular donor(D)chromophore(C)acceptor(A) triad utilizing a micellar interface. Alkyl viologen (A(2+)) is adsorbed on the hydrophilic interface of Triton X-100 micelle, which bears D units in the hydrophobic core. Excited triplet state of a hydrophobic flavin C entrapped in the supercage gives rise to primary ET from D, which is followed by the secondary ET from C to A(2+) to give the long-lived (>10 mu s) charge-separated state with negligible yield of escaped C. Analysis of magnetic field effect reveals that diffusion of C from the core to the hydrophilic interface leads to long-distance ET with a low charge recombination yield of similar to 20%. This novel concept of dynamic charge transporter has important implications for development of photon-energy conversion systems in solution phase.

DOI： 10.1021/jz502495u

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We demonstrate the magnetoconductance (MC) effect originated from depressing the spin mixing in encounter pairs under the external magnetic field provides quantitative information about the singlet fission, the charge recombination, and the trap-related dynamics with triplet exciton in a bilayer device of pentacene (Pen) and fullerene (C-60). Three MC effects in low-, moderate-, and high-fields were detected in the bilayer device at room temperature. Kinetic analysis of the low-field MC effect showed that the charge recombination yield at the Pen|C-60 interface is similar to 1%. Quantum mechanical simulations for dynamics of spin-carrying pairs following the conservation rule of spin angular momentum in recombination showed that the moderate- and high-field MC effects are caused by, respectively, the trap-related dynamics with triplet exciton and the singlet fission with a maximum yield of 52% in the layers. The quantitative information obtained by investigating the MC effect will contribute to the development of high-efficiency organic solar cells devices.

DOI： 10.1021/jp508799j

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Authorship：Last author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Chemical Society of Japan  

The thermal annealing effects on the photocarrier dynamics in thin films of [6,6]-phenyl C₆₁ butyric acid methyl ester (PCBM) on quartz substrates are investigated. Both the photocarrier generation via charge-transfer state and the charge transport in PCBM films are studied by time-resolved photoconductance (PC) measurement. More than 90% of external photocarrier generation efficiency relative to the non-annealed film is reduced upon annealing of the PCBM film at high temperatures. Excitation light power dependence of PC indicates that the photocarrier in the non-annealed film is generated by a one-photon process, while photons of more than one are required in highly annealed films. The multiphotonic process for carrier generation and the substantial reduction of carrier density caused by the thermal treatment are associated with trap formation. The density of photoinjected carrier is also affected by applying external magnetic field. The observed positive magnetophotoconductance (MPC) in non-annealed film is understood in terms of the incoherent spin conversion in nongeminate electron–hole (e–h) pairs with a selective recombination from singlet e–h pairs. In highly annealed film, the broad magnetic field dependence of MPC with negative phase is suggested to originate from the detrapping of trapped carrier assisted by collision with the triplet exciton.

DOI： 10.1246/bcsj.20130097

CiNii Article

CiNii Books

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/jp402640k

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DOI： 10.1007/s10765-012-1296-8

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Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.physe.2011.02.010

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

DOI： 10.1002/smll.201001344

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DOI： 10.1016/j.synthmet.2009.10.003

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.synthmet.2009.08.052

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/jp802810s

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.cplett.2008.03.089

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

Several azulene-substituted thioketones, 1-thiobenzoylazulene (1a) and di(1-azulenyl) thioketone (2a) and their derivatives (1b and 2b-d) with alkyl substituents on each azulene ring, were prepared and their intramolecular pericyclization reaction was examined. The thioketones with a 3-alkyl substituent on each azulene ring exhibited the presumed pericyclization reaction under thermal and acid-catalyzed conditions, although the cases of the 1-azulenyl thioketones without the 3-alkyl substituents afforded a complex mixture under similar conditions. The intramolecular reaction following the intramolecular hydrogen transfer afforded the products 13b, 14b, and 14c. The products 13b and 14b were converted into the corresponding cations 18(+) and 19(+), which have structural similarity with that of the phenalenyl cation. These cations exhibited the expected two-step reduction waves upon CV, although the ESR analysis revealed that the neutral radical state did not have the presumed high stability.

DOI： 10.1021/jo702309b

PubMed

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

DOI： 10.1002/cphc.200600621

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.cplett.2007.01.067

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Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/ja061507y

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Informa UK Limited  

The radical sites generated by the visible light irradiation of nitrogen-doped TiO2 particles prepared by a mechanochemical method have been studied using cw-EPR spectroscopy. The powders prepared by planetary milling of the anatase TiO2 with urea clearly show an absorption in the visible region, indicating doping of nitrogen. Visible light irradiation with wavelengths longer than 420nm induces a nitrogen-centred radical site. The radical site is assigned to the interstitial NO22- radical. In the presence of air, a reversible response of the growth and decay of paramagnetic sites was observed during and after photolysis. In contrast, in degassed samples, the decay of the NO22- signals is accompanied by the concomitant growth of the neutral NO radical site after irradiation, suggesting breaking of the N-O bond.

DOI： 10.1080/00268970600551387

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/jp0565857

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Chemical Society of Japan  

A significant wavelength dependence of the excitation light was observed in the magnetic field effects (MFE) on the photocarrier generation of a benzene-1,2,4,5-tetracarbonitrile-doped poly(N-vinylcarbazole) film. The excitation of the carbazole induces positive MFEs, indicating an enhancement of the photoconductivity originating from the charge separation through the triplet exciton. In contrast, a singlet spin state governs the photocarrier generation in the case of the charge transfer band excitation, because negative MFEs are induced.

DOI： 10.1246/cl.2005.1424

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DOI： 10.1021/es048299z

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.cplett.2005.06.066

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Wiley  

DOI： 10.1002/anie.200461681

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Using the multifrequency time-resolved electron-spin-resonance (TRESR) method, we have investigated the carrier-generation dynamics in a photoconductive film sample of poly(N-vinylcarbazole), The TRESR spectra, due to spin-polarized geminate electron-hole (e-h) pairs captured in deep-trap sites, were observed at several fields that were achieved using microwaves with different frequencies, The spectra detected at room temperature were interpreted in terms of the ST0 polarization in trapped e-h pairs and the ST+ polaritation induced in canonical e-h pairs. The spectral simulation clarified the distribution of e-h separation distance (r) and the r-dependent recombination of the trapped pairs. The initial spatial distribution of the trapped e-h pairs exponentially decreased with an increase in r. There is no large population of long-distant c-h pairs with r &gt; 1.5 nm. Based on the appearance of the ST+ polarization in the long-distant pairs that is generated in middle-distant pairs and the initial exponential distribution of the trapped pairs, it was concluded that stepwise hole hops rather than a long-range hole jump represent the proper dynamics of the geminate pair in the charge-separation process. The r-dependent recombination rate suggests a single-step tunneling recombination of the trapped pairs.

DOI： 10.1103/physrevb.71.195206

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/jp0453212

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/jp044475e

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/jo048489s

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/jo035053o

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

y using MO calculations based on DFT, absorption, and fluorescence spectroscopy, we have comprehensively studied the low-lying excited singlet states of alpha,omega-diphenylpolyynes (DPY) having 1-6 triple bonds. The a(g) vibrational modes of the CdropC stretching and of the phenyl ring motion were observed in the fluorescence spectra of diphenylacetylene and 1,4-diphenylbutadiyne. On the other hand, in the fluorescence spectra of the long DPY with the triple-bond number (N) more than two, the phenyl ring motion with ag symmetry disappeared and the big modes of the phenyl ring twisting (similar to400 cm(-1)) and of the C-H bending (similar to900 cm(-1)) were detected. The observed fluorescent states of DPY with N less than or equal to 2 and N greater than or equal to 3 are assigned to the 1(1)B(1u) (pi(x)pi(x)(*)) and 1(1)A (pi(x)pi(y)(*) and/or pi(y)pi(x)(*)) states, respectively, based on the vibronic structures, the relatively short lifetimes, and the solvatochromic shifts of the fluorescence spectra. Not only the allowed transition of 1(1)B(1u) &lt;-- So but also the forbidden transition of 1(1)A(u) &lt;-- S-0 was detected in the fluorescence excitation spectra of the long DPY with N greater than or equal to 3. The low-lying excited state with A(u) symmetry is characteristic in polyyne, which does not exist in polyene. The oscillator strength (f) of the first absorption band in DPY decreases with an increase in N, which is the opposite behavior of the all-trans-alpha,omega-diphenylpolyenes. The N-dependence of the f value is understood by the configuration interaction between the 1(1)B(1u) and 2(1)B(1u) (pi(y)pi(y)(*)) states, which is consistent with the reduction of the nonlinear optical response of polyyne.

DOI： 10.1021/ja035173d

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/bf03166633

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

We have studied the defect structures and mechanism for the luminescence of non-doped, Tb3+-doped and Tb3+-Zn2+ codoped alumina films treated at various temperatures from 300 to 800°C. The electron paramagnetic resonance (EPR) spectra observed before UV-irradiation are attributable to the non-bridging oxygen radicals Al-O-O at treatment temperatures of 300-500°C and Al-O at 800°C. The UV-light irradiation of the non-doped alumina films gives the EPR spectra with the 27Al hyperfine splitting. There exists a good correlation between the treatment temperature dependence on the light-induced EPR signal intensity of the trapped electron and the NMR peak intensity due to the five-coordinated aluminum ion. We concluded that the electron is captured at the oxygen vacancy connected with the five-coordinated aluminum. The broad EPR spectra due to the ground state of the Tb3+ ion were observed in the Tb3+-doped and Tb3+-Zn2+ codoped alumina films. The Tb3+ concentration dependence of the EPR signal intensity due to the non-bridging oxygens suggests that Tb3+ prefers to form Al-O-Tb bonds and prevent to form a cluster of rare earth ions itself. The light-induced EPR signal of the electron trapped at oxygen vacancy next the five-coordinated aluminum was also observed for the Tb3+-Zn2+ codoped alumina film, which produced a long-lasting luminescence. The photogenerated trapped electron remained for several minutes under the room temperature. These experimental facts indicate that the five-coordinated aluminum ions act as the trapping sites to produce the long-lasting luminescence. © 2002 Published by Elsevier Science Ltd.

DOI： 10.1016/s0022-3697(02)00377-3

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

DOI： 10.1021/ja029443o

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Informa UK Limited  

The substrate specificities of deuterolysin, a 19-kDa zinc-protease (EC 3.4.24.39) from Aspergillus oryzae, were investigated at pH 9.0 with various fluorogenic acyl-peptide-4-methylcoumaryl-7-amides (peptide-MCAs). N-Butoxycarbonyl-Arg-Val-Arg-Arg-MCA was the best substrate for deuterolysin. We therefore measured its kinetic parameters. Deuterolysin had high activity toward the peptide bonds next to pairs of basic residues in calf thymus histone H4. The specificity of cobalt-substituted deuterolysin (Co-deuterolysin) for peptide-MCAs was similar to that of native deuterolysin. The CD spectrum of Co-deuterolysin was similar to that of the native deuterolysin. The metal coordination sphere of Co-deuterolysin was analyzed by Q-band (33.9570 GHz) electron paramagnetic resonance (EPR) spectroscopy. Using computer simulation of EPR, we found the g principal values to be g(xx) = 5.20, g(yy) = 4.75, and g(zz) = 2.24; the metal center was a divalent cobalt ion in a high spin state.

DOI： 10.1271/bbb.67.264

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DOI： 10.1103/physrevb.66.014423

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

Continuous-wave time-resolved EPR (cw-TREPR) and pulsed electron nuclear double resonance (ENDOR) studies have been carried out to clarify the electronic structure of the lowest excited triplet (T,) state of 5,12-naphthacenequinone (5,12-NpQ) as well as 1,4-anthraquinone (1,4-AQ) and 6,13-pentacenequinone (6,13-PeQ). The T, energy level and the D value of the zero-field splitting (ZFS) parameters only slightly decreased with the increasing pi-conjugated system. The T-1 states of these linear para-acenequinones were assigned to the pipi* character. In triplet 5,12-naphthacenequinone, more than 80% of the unpaired electron spins are localized on the naphthalene aromatic sub-system. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/s1386-1425(01)00710-7

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Pulsed electron paramagnetic resonance (EPR) spectroscopy has been applied to elucidate the radical structures of Argonne premium coals and the reaction processes in coal tar pitches (CTP). Using two-dimensional nutation spectroscopy, the main EPR signals around g = 2.00 for the coals were confirmed to be attributed to free radicals rather than spin clusters with higher spin multiplicities. The broad H-1- and C-13-hyperfine spectra of the coals were detected separately by hyperfine sublevel correlation (HYSCORE) spectroscopy. It is concluded that the main coal radicals are pi radicals delocalized in pericondensed aromatic hydrocarbons with more than seven aromatic rings, which are larger than those of the most probable aromatic molecules in coals. HYSCORE spectroscopy, furthermore, helped us to understand the chemical change in the cation radicals in the charge-transfer complexes that accelerate the dehydrogenative polymerization of I-2-treated CTP.

DOI： 10.1021/ef010148j

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Grinding a mixture of 3-chlorobiphenyl (BP-Cl) and CaO with or without the addition of quartz was conducted in air by a planetary ball mill to investigate the mechanochemical dechlorination of BP-Cl. The dechlorinating reaction proceeds with an increase in grinding time, and over 99% of BP-Cl is decomposed at 360 min. Washing the ground sample with different solvents results in different products. Addition of quartz to the grinding mixture facilitates dechlorination efficiency, especially in the case of a high weight ratio of BP-Cl to CaO.

DOI： 10.1021/es010638q

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For the first time, we detected paramagnetic products generated during the grinding of 3-chlorobiphenyl (BP-Cl) with calcium oxide (CaO) nanoparticles by a ball mill method, which is one of the promising ways to detoxify hazardous chlorinated organic compounds. Those products were assigned to oxygen-centered aromatic radicals coming from BP-Cl and trapped electrons in oxygen vacancies on the surfaces of the CaO reactants using high-frequency and pulsed electron paramagnetic resonance spectroscopies. The observed good correlation between the dechlorination efficiency and the radical yield suggests that a radical mechanism plays an important role in the destruction of organochlorine compounds. The mechanochemical dechlorination could be interpreted by the following mechanism. First of all, the mechanical stressing induces the electron transfer from O2- sites on the surface of the CaO particle to the organic compounds. The produced organic anion radicals then undergo the effective self-dissociation of a chlorine-carbon bond.

DOI： 10.1246/bcsj.74.2303

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Copper(II), zinc(II), and nickel(II) complexes with tridentate imino nitroxyl diradicals, [CuCl(bisimpy)(MeOH)]-(PF6) (1), [ZnCl2(bisimpy)] (2), and [NiCl(bisimpy)(H2O)(2)]Cl . 2H(2)O (3) (bisimpy = 2,6-bis(1'-oxyl-4',4',5',5'-tetramethyl-4',5'-dihydro-1'H-imidazol-2'-yl)pyridine), were prepared, and their magnetic properties were studied. In 1, the Cu(II) ion has a square pyramidal coordination geometry, of which the equatorial coordination sites are occupied by three nitrogen atoms from the bisimpy and a chloride ion. The coordination geometry of the Zn(II) ion in 2 can be described as a trigonal bipyramid, with two chloride ions and a bisimpy. In 3, the Ni(II) ion has a distorted octahedral coordination geometry, of which four coordination sites are coordinated by the bisimpy and chloride ion, and two water molecules occupy the remaining cis positions. Magnetic susceptibility and EPR measurements revealed that in 1 and 3 the Cu(II) and Ni(II) ions with imino nitroxyl diraicals were ferromagnetically respectively, and the coupled, with the coupling constants J (H = -2J(ij)SigmaS(i)S(j)) of +165(1) and 109(2) cm(-1), intraligand ferromagnetic interactions in 1-3 were very weak. DFT molecular orbital calculations were performed on the diradical ligand, 1, and 2 to study the spin density distribution before and after coordination to the metal ions.

DOI： 10.1021/ic0102384

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DOI： 10.1002/1521-3773(20010903)40:17<3234::aid-anie3234>3.0.co;2-b

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

The lowest excited triplet (T-1) states of diphenylacetylene and several alpha,omega -diphenylpolyynes (DPY) having two, three, four and six triple bonds were studied using continuous wave time-resolved electron paramagnetic resonance (CW-TREPR), pulsed EPR, and phosphorescence spectroscopy. Linear and planar molecular structures in the T-1 states of DPY were suggested from the magnetophotoselection experiments and observation of a strong 0-0 band in the well-resolved phosphorescence spectra. The spin density distributions, which were obtained by electron spin echo envelope modulation measurements and semi-empirical molecular orbital calculations, and the phosphorescence polarization normal to the long axis of molecule for the 0-0 bands suggested that the T-1 states of DPY have a B-3(1u) (pi (x)pi (x)*) electronic configuration. DPY showed an abnormally large \D\ value of the zero-field splitting parameters that increased with increasing molecular size. Such an unusual behavior of the D values is interpreted in terms of the spin-orbit interaction between the T-1 and (3)A(u)(pi (x)pi (y)*) states mainly due to their energy proximity which is probably characteristic of the excited states for the polyynes. The estimated energy gap between the (3)pi (x)pi (y)* and (3)pi (x)pi (x)* states for DPY ranges from 2900 cm(-1) to 1400 cm(-1). There existed a good correlation between the acceleration of the nonradiative decay rate constant from the T1 state and appearance of a ring twisting vibronic band with b(1g) symmetry in the phosphorescence spectra for DPY. Therefore, we concluded that the vibronic interaction between the (3)pi (x)pi (y)* and (3)pi (x)pi (x)* states promoted by the b(1g) vibration leads to a broadening of the potential surface of the T-1 state which results in the fast radiationless decay Co the ground state, (C) 2001 American Institute of Physics.

DOI： 10.1063/1.1331614

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Using two-, three- and five-pulse methods, we have measured the electron spin echo envelope modulation (ESEEM) of a stable paramagnetic center existing in a non-doped ladder polymer, in which two polydiacetylenes are conjugated in each repeating unit. A relatively deep modulation effect owing to weak hyperfine interaction with protons was observed. The number of interacting protons was estimated to be a few tens based on the analysis of the modulation amplitude. The interaction with many protons implies that the paramagnetic center in the ladder polydiacetylene also possesses a wavefunction delocalized on several units in the pi -conjugated system like the spin solitons in polyacetylene. (C) 2001 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/s0038-1098(00)00471-3

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Dangling bond (DB) defects in unhydrogenated microcrystalline silicon (mu c-Si) prepared by rf sputtering have been studied. Raman spectra and x-ray diffraction indicate that the mu c-Si fraction has been formed at the Ar sputtering pressure higher than 26.6 Pa while only amorphous silicon (a-Si) has been produced at the lower pressure. The electron paramagnetic resonance (EPR) spectrum in the mu c-Si film is broad and unsymmetrical with the average g value of g=2.006 compared with that of a-Si (g=2.0055). The X- and Q-band EPR measurements suggest that the line shape is mainly governed by the inhomogeneous broadening due to the g anisotropy, indicating relatively large distribution of the structure of the DB defects. (C) 2000 American Institute of Physics. [S0021-8979(00)06712-8].

DOI： 10.1063/1.373875

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We report electron paramagnetic resonance (EPR) studies in dangling bond (DB) defects in the hydrogenated microcrystalline silicon (mu c-Si:H) film prepared by a plasma enhanced chemical vapor deposition (PECVD), unhydrogenated microcrystalline silicon (mu c-Si) film prepared by RF sputtering, and mu c-Si embedded in SiO2 film formed by co-sputtering followed by annealing. Multi-band EPR measurements showed that their line widths originate primarily from a distribution of the g-values. We have detected a signal at g = 2.006 in the microcrystalline fraction of the mu c-Si, mu c-Si:H and mu c-Si embedded SiO2 films. The signal has a greater width than the DB signal in amorphous silicon (a-Si), indicating a larger distribution of g-values of the defects in the microcrystalline material. The DB signal in the mu c-Si embedded in SiO2 was reproduced by the computer simulation taking into account the distribution of the g-values. (C) 2000 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/s0022-3093(00)00027-2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

We have examined Raman scattering, X-ray diffraction, electron paramagnetic resonance (EPR) spectra and the conductivity of nitrogen-doped hydrogenated microcrystalline silicon. The EPR signals due to conduction electrons have been observed in the doped films, except for highly doped samples that have no microcrystalline fraction. The result indicates that the doped nitrogen atom acts as an electron donor in the microcrystalline silicon. The temperature dependence of the conductivity clarify that the activation energy depends on the doping level. The influence of the doping level on the conductivity can be interpreted in terms:of the balance of the effective electron donation and the decrease of carrier mobility due to a decrease of the microcrystalline phase volume ratio. At temperatures lower than approximately 180 K, the conductivity shows little variation. This is explained using a model of the hopping conduction, in terms of defect states for all samples.

DOI： 10.1143/jjap.39.31

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Iodine introduced into coal tar pitch (CTP) can drastically alter its reology and carbonization behavior. Here, the mechanism of interaction between iodine and CTP has been investigated by using various spectroscopic methods such as I-127-NMR, EPR and FT-IR. It is shown that some iodine molecules infiltrated into the CTP and form charge transfer complexes with the relative large aromatic components of the CTP. Hyperfine sublevel correlation spectroscopy (HYSCORE) revealed the molecular size of cation radicals, which contain more than ten benzene rings, and the location of iodine anion that is incorporated at ca. 0.3 nm from the aromatic cation radicals. The elemental H/C ratio decreased and the viscosity of CTP increased with the density of the charge-transfer complexes, which was also increased by the iodine treatment. These results strongly suggest that dehydrogenative polymerization of CTP occurs during the iodine treatment. The cation radicals in the charge-transfer complexes accelerate the dehydrogenative polymerization and result in a high carbon yield. (C) 2000 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/s0008-6223(00)00022-1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

Reactions of [Fe-II(CN)(2)(bpy)(2)] and [Fe-III(CN)(2)(bpy)(2)](PF6) with [Cu-II(bpy)(CH3OH)(2)](PF6)(2) in methanol yielded cyanide-bridged cyclic tetranuclear complexes of [(Fe2Cu2II)-Cu-II(mu-CN)(4)(bpy)(6)](PF6)(4). 2H(2)O . 4CHCl(3) (1) and [Fe-2(III)-Cu-2(II) (mu-CN)(4)(bpy)(6)](PF6)(6) . 4CH(3)CN . 2CNCl(3) (2), respectively. Zn the squares of 1 and 2, the Fe2+/3+ (low-spin) and Cu2+ ions are alternately bridged by the cyanide ions, the carbon atoms of which coordinate to the iron ions. Variable-temperature magnetic susceptibility studies of complexes revealed that the Cu2+ ions in 1 are magnetically isolated. In the square of 2, the adjacent Fe3+ and Cu2+ ions were ferromagnetically coupled through the cyanide bridges with a J(1) value of +6.3(1) cm(-1) and the weaker antiferromagnetic interactions between the orthogonal Fe3+... Fe3+ and Cu2+...Cu2+ pairs are operative (J(2) = -3.1(1) cm(-1)). The propagation of the ferromagnetic interaction in 2 can be understood by the orthogonal magnetic orbitals of the low-spin Fe3+ (d pi) and Cu2+ (d sigma) ions. Cyclic voltammograms of the squares have been recorded and discussed. Crystal data for 1: triclinic space group P (1) over bar, a = 14.491(4) Angstrom, b = 15.312(4) Angstrom, c = 12.959(3) Angstrom, alpha = 91.38(2)degrees , beta = 109.56(2)degrees, gamma = 65.41(2)degrees, Z = 1. Crystal data for 2: triclinic space group P (1) over bar, a = 14.472(9) Angstrom, b = 15.310(6) Angstrom, c = 12.523(5) Angstrom, alpha 102.58(3)degrees beta = 107.19(4)degrees, gamma = 75.08(4)degrees, Z = 1.

DOI： 10.1021/ic990617l

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We have measured the excitation spectra for tropolone-OH in durene single crystal and tropolone-OD in deuterated durene using a time-resolved electron paramagnetic resonance (TREPR) detection method that makes possible to separate the signals due to magnetically different sites. The tunneling doublet with 3 cm(-1) was observed in the sharp zero-phonon line. The small splitting indicates that the crystal field increases the barrier of double-minimum potential for the proton tunneling in the S-1 state. Moderately asymmetric potentials of the S-0 and S-1 states, where the energetic imbalance between two wells in the S-1 state potential is opposite the S-0 state potential, reasonably explained the observed unusual intensity ratio of the tunneling doublet (0(1)(+) &lt; 0(1)(-)). A well-resolved progression of a phonon band with a 15 cm(-1) separation was also obtained in durene crystal at very low temperature. From a Franck-Condon analysis of the relative intensity of the phonon band, it was clarified that the stable configuration of the excited state tropolone in durene differed from that of the ground state. (C) 1999 American Institute of Physics. [S0021-9606(99)00439-0].

DOI： 10.1063/1.479980

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Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

Unusually large \D\ values of zero-field splitting parameters were observed for 1,6-diphenylhexatriyne (\D\ = 0.396 cm(-1)) and 1,8-diphenyloctatetrayne (\D\ = 0.533 cm(-1)) by using time-resolved EPR (TREPR) spectroscopy. The lowest excited triplet (T-1) states of these diphenylpolyynes were assigned to B-3(1u)((3)pi(x)pi(x)(*)) in character from the degree of the polarization of phosphorescence. It has been concluded that the present diphenylpolyynes have a linear planar structure in the T-1 states, although the TREPR and phosphorescence spectra indicate interactions between the T-1((3)pi(x)pi(x)(*)) and T-n((3)pi(x)pi(y)(*)) states through spin-orbit and vibronic interactions. (C) 1999 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/s0009-2614(99)00189-x

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Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：Informa UK Limited  

Employing X- and Q-band time-resolved EPR and pulsed EPR techniques, we have investigated effects of twist conformation on the electronic structures and magnetic properties of the lowest excited triplet states of alkyl phenyl ketones. The conformational variation due to steric hindrance of a bulky substituent on the alpha-position drastically leads to a decrease of the zero-field splitting constant of |D| and an increase of the energy gap between 3np* and 3pp* states. Hydrogen bonding with H2O destabilized significantly the 3np* state and switched the T1 state to the 3pp* state. t-Butyl phenyl ketone gave unusually broad EPR spectra in rigid glassy matrices. The multifrequency and pulsed EPR measurements clarified that the inhomogeneously broadening spectra were ascribable to the distribution of the dihedral angle about a twist conformation. Asymmetric distribution of the ZFS parameters was interpreted in terms of the perturbation of spin-orbit interactions to the spin sublevels.

DOI： 10.1080/00268979909483018

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Authorship：Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

Hyperfine sublevel correlation spectroscopy (HYSCORE) spectra have been measured for the radicals in eight well-characterized Argonne Premium coals and their model compounds. The broad H-1 and C-13 hyperfine spectra of all coals were detected at room temperature. The hyperfine structure was analyzed by the comparison with model radicals and semiempirical molecular orbital calculations. The main coal radicals are considered as two-dimensionally condensed pi radicals with more than seven aromatic rings. The C-13/H-1 ratio of the hyperfine spectra increases with coal rank, suggesting a new index of coal rank.

DOI： 10.1021/ef980130h

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

Two-dimensional electron paramagnetic resonance (BD-EPR) spectra of Illinois No. 6 and Upper Freeport coals have been measured. From 2D-nutation spectroscopy, it is confirmed that the main EPR signal around g = 2 is attributed to free radicals, but not to radical pairs. Both coals showed nuclear modulation effects due to H-1 and naturally abundant C-13 nuclear spins. Spin-echo correlation spectroscopy (SECSY) experiments elucidate the distribution of modulation frequencies included in a broad EPR spectrum. The observed dip in the C-13 matrix spectrum obtained from SECSY is interpreted in terms of the decrease of vitrinite radicals, which are weakly interacting with C-13 nuclei, in the central region of the EPR spectrum. The analysis of the broad hyperfine spectra due to H-1 and C-13 nuclei in the hyperfine sublevel correlation spect-ra suggests the existence of several kinds of radicals in coal. Most of unpaired electrons are considered to be trapped in aromatic rings. The ratio of C-13/H-1 of hyperfine spectra increases with coal rank, suggesting a new index of coal rank.

DOI： 10.1021/ef980053q

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

The short-lived T-1 state of 1,4-diphenylbutadiyne (DPB) has been investigated in various glassy matrices at low temperatures using time-resolved EPR and pulsed EPR methods. Zero-field splitting parameters of D = -0.250 cm(-1) and E = +0.018 cm(-1) were determined. The negative D value was verified from the M-S dependence of the ENDOR frequencies. The hyperfine splitting constants of ring protons were obtained from the electron spin-echo envelope modulation with three-pulse stimulated echo. The spin density distribution on the phenyl groups was estimated from the analysis of the hyperfine splittings at each of the canonical orientations. The moderate spin densities on the phenyl rings indicated that the T-1 state was (3)pi(x)pi(x)* in electronic character. The origin of the large negative D value of DPB has been discussed in terms of the spin-orbit interaction between the close lying (3)pi(x)pi(x)* and (3)pi(x)pi(y)* states.

DOI： 10.1021/jp9812740

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

Rare earth ion (Er3+, Eu3+ and Sm3+)-doped alumina films have been prepared by the sol-gel method, using AlCl3-derived alumina sol. The effects of dopant concentration and treatment temperatures on the photo-properties of absorption and emission have been examined for the doped films. These sol-gel-derived alumina matrices gave a high-dopant concentration(similar to 15 mol% per alumina). (C) 1998 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/s0009-2614(98)00132-8

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society (APS)  

A high-frequency (95 GHz) and conventional-frequency (9.3 GHz) pulsed electron paramagnetic resonance and electron-nuclear double resonance (ENDOR) study is reported on the deep boron acceptor in 6H-SiC. The results support a model in which the deep boron acceptor consists of a boron on a silicon position with an adjacent carbon vacancy. The carbon vacancy combines with a boron along the hexagonal c axis. It is concluded that 70-90% of the spin density resides in the silicon dangling bonds surrounding the vacancy and another 9% on the neighboring carbon atoms. The spin-density distribution is more localized than in the case of the shallow boron acceptor as deduced from the ENDOR experiments.

DOI： 10.1103/physrevb.57.1607

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Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.57.1607/fulltext

Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

Time-resolved electron paramagnetic resonance experiments on the short-lived Ti state of nenphosphorescent tropone were carried out using mixed crystals. Well-resolved hyperfine splittings due to allowed and forbidden transitions were observed at principal axes of the zero-field tenser. The spin density distribution, C-H bond angles, and the sign of the D value were deduced from the hyperfine spectra. It has been concluded that the T-1 state of tropone mainly has a (3) pi pi* configuration and holds its molecular structure of C-2v symmetry. The experiments and molecular orbital calculations indicate that the large Franck-Condon factor between the T-1 and the So states arises from the change of the potential surfaces due to the antibonding character of the pi* orbital at the C-4-C-5 bond in the T-1 state.

DOI： 10.1021/jp9721154

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1023/a:1006517219037

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Royal Society of Chemistry (RSC)  

Time-resolved EPR measurements and semi-empirical MO calculations have been carried out to clarify the electronic structure of the T-1 state of nonphosphorescent tropolone. The observed zero-field splitting parameters indicate that the T-1 state has a pure pi pi* character and the energy order among the spin sublevels was T-Y (in-plane) > T-X (in-plane) > 0 > T-Z (out-of-plane), which is the same as tropone for a parent molecule. However, the principal X-axis slightly turns out of the carbonyl bond direction so that the intersystem crossing from the S-1 state to the T-Y sublevel becomes more active. The spin densities obtained from hyperfine splittings of protons and MO calculation of AM1 method show an asymmetric distribution of unpaired pi-electrons over two oxygens as well as the seven-membered ring. This unbalanced distribution makes the deviation of the X-axis from the carbonyl bond clear. We found two sites that can exchange each other by intramolecular proton transfer in a durene single crystal.

DOI： 10.1039/a708678d

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Publishing type：Research paper (scientific journal)   Publisher：Trans Tech Publications, Ltd.  

DOI： 10.4028/www.scientific.net/msf.258-263.703

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Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

Phosphorescence and TREPR spectra have been measured for 2-methyl-1,4-naphthoquinone (MNQ), 2,3-dimethyl-1,4-naphthoquinone (DMNQ), and 2-methoxynaphthoquinone (MeONQ) in several matrices at low temperatures. The \D\ value of ZFS parameter decreases with increasing the electron-donating character of the substituent group. For MNQ, the T-1 state is clearly assigned to be (3)n pi* in character. The broad phosphorescence spectra and minor effects of the matrix polarity on the ZFS parameters lead to the conclusion that the character of the T-1 states are mainly 3 pi pi* in DMNQ and MeONQ. The T-1 states of the present naphthoquinone derivatives have more or less mixed character of the 3n pi* and 3 pi pi* states.

DOI： 10.1021/jp971818i

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

An orthogonal arrangement of imino nitroxide ligands in Cu-I and Ag-I complexes results in propagation of an intramolecular ferromagnetic interaction between the coordinated imino nitroxides through these diamagnetic ions. Reaction of [Cu-I(CH3CN)(4)](PF6) and Ag-I(PF6) with imino nitroxides in ethanol solution gave [Cu-I(immepy)(2)-(PF6) (1) and [Ag-I(impy)(2)](PF6) (2), respectively (immepy 2-(2-(6-methylpyridyl))-4,4,5,5-tetramethyl-4,5-dihydro-1H imidazolyl-l-oxy and impy 2-(2-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxy). Complex 1 crystallizes in the orthorhombic space group Pba2, which has a unit cell with a 11.251(2) Angstrom, b = 14.745(3) Angstrom, c = 9.747(2) Angstrom, V = 1617.0(5) Angstrom(3), and Z = 2. Refinement with 991 reflections observed [\I-0\ &gt; 3 sigma(I-0)] gave R = 0.044 (R-w = 0.053). In 1, imino nitroxides coordinate to the Cu-I ions in a tetrahedral fashion, the dihedral angle between coordinating imino nitroxides being 88.7 degrees. Magnetic susceptibility measurement for 1 shows typical triplet-singlet behavior with strong ferromagnetic interactions (J = 55.1(6) cm(-1) with g = 2.0; H = -JS(1).S-2) The UV-visible absorption spectrum of 1 shows strong bands at 454 and 766 nm assignable to charge-transfer bands from the Cu ion to the ligand NLUMO and SOMO, respectively. The pi-back-donation to the SOMO induces the spin on the Cu ion and results in the strong ferromagnetic interaction. Complex 2 crystallizes in the orthorhombic space group P2(1)cn which has a unit cell with a = 10.535(6) Angstrom, b = 31.295(3) Angstrom, c 8.921(4) Angstrom, V = 2941(1) Angstrom(3), and Z = 4. Refinement with 1882 reflections [\I-0\ &gt; 3 sigma(I-0)] gave R = 0.058 (R-w = 0.074). Ln 2, the four coordination sites of the Ag-I ion were completed with two imino nitroxides and the dihedral angle between the imino nitroxides is 79.2 degrees. The EPR spectrum of a frozen ethanol solution of 2 shows a typical triplet signal with zero field splitting (\D\ = 0.043 cm(-1) and \E\ = 0.014 cm(-1)). Curie plots for the rim = 2 signal below 80 K gave a positive Weiss constant (theta = 4 K), suggesting an intramolecular ferromagnetic interaction in 2.

DOI： 10.1021/ic960939e

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Publishing type：Research paper (scientific journal)   Publisher：Informa UK Limited  

Orthogonal arrangement of iminonitroxides in [CuI(immepy)2](PF6) (1) and [AgI(impy)2](PF6) (2) results in propagation on intramolecular ferromagnetic interaction between coordinating iminonitroxides through these diamagnetic ion. In 1, iminonitroxides coordinate to the CuI ion in a tetrahedral fashion, the dihedral angle between coordinating iminonitroxides being 88.7 degrees. Magnetic susceptibility and epr measurements for 1 show the typical ferromagneic behavior with large zero field splitting (2J = 91(1) cm-1 (H = -2JS1S2); D = 3.62 cm-1). In 2, the four coordination sites of AgI ion were completed with two iminonitroxides and the dihedral angle between the iminonitroxides is 79.2 degrees. Temperature dependence of teh epr spectra for frozen ethanol solution of 2 shows that the intramolecular mangetic interaction between radicals is ferromagnetic (q = 4 K).

DOI： 10.1080/10587259508031841

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

Time-resolved EPR and phosphorescence spectra have been observed for the lowest excited triplet states of 4-nitropyridine N-oxide and its alkyl derivatives. It has been shown that the ratio of the zero-field-splitting (zfs) parameters reflects the molecular geometry: the |E/D| value decreases with increasing the twisting angle of the nitro group from the molecular plane. Protic solvents induce significant changes in the zfs parameters and the population ratio of the triplet sublevels. The results are discussed in terms of formation of the hydrogen bonding complex at the N-oxide oxygen atom.

DOI： 10.1021/j100008a009

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Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

Transient triplet EPR spectra of two types of spirans, spiro[9,10-dihydro-9-oxoanthracene-10,2'-benz[f]indan] and spiro[9,10-dihydro-9-oxoanthracene-10,2'-3H-phenalene],were measured in a glassy matrix at 77 K. Spin polarization conservation during the intramolecular triplet-triplet energy-transfer process was observed. The results clearly indicate that spin orientation is conserved in the molecular frame in the presence of an external magnetic field and that the high-field approximation cannot explain the spin polarization pattern observed in the X-band EPR spectra. The results contribute to the understanding of the relaxation processes of the excited states.

DOI： 10.1021/ja00091a042

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The T1 states of nonphosphorescent 2,3-benzotropone and phosphorescent 4,5-benzotropone were studied by a time-resolved EPR method. For 2,3-benzotropone, the observed magnetic parameters and the decay rate (the average decay rate 1.1 x 10(5) s-1 at 4.2 K) are very similar to those of the parent tropone. On the other hand, 4,5-benzotropone has different magnetic properties and a much slower radiationless decay rate (&lt;30 s-1) than tropone. The mechanism of the fast radiationless transition between the T1 and S0 states of tropone has been discussed.

DOI： 10.1021/j100104a008

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The magnetic property and decay kinetics of the nonphosphorescent triplet (T1) state of tropone in glassy matrices have been studied by employing the time-resolved EPR (TREPR) method with excimer and dye laser excitations. The T1 state was assigned to be nearly pure 3pp* in character from the small zero-field splitting (zfs) parameters (|D| = 0.077 cm-1 and |E| = 0.011 cm-1 in a toluene glassy matrix) and their small dependency on the matrix polarity. The directions of the principal axes of the zfs tensor were determined by magnetophotoselection experiments with two colors of lasers. It was found that the T1(pp*) state of tropone has very short lifetime; the average rate constant from the zero-field spin sublevels is 2 x 105 s-1.

DOI： 10.1021/j100172a003

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Chemical Society (ACS)  

Photochemical hydrogen abstraction reactions and the lowest excited triplet states taking part in the initial process have been investigated for several pyridine derivatives by using the time-resolved EPR method. The emissive CIDEP spectrum obtained from the laser photolysis of 4-acetylpyridine (1) in 2-propanol was assigned to the corresponding ketyl radical, proving initial hydrogen abstraction by the carbonyl group. In the cases of 4-cyano-(2) and 4-methoxycarbonyl-(3) pyridines, and 4-pyridinecarboxamide (4), enhanced absorptive CIDEP spectra due to the corresponding 1-hydropyridinyl radicals were observed, suggesting the preferential population to the lowest sublevel in the intersystem crossing. The triplet EPR and phosphorescence spectra observed at 77 K indicate that T1 of 1 is mainly the carbonyl np* state with a small contribution from the pp* state. The T1 states of 2, 3, and 4 are considered to be of mixed character between the pyridine 3B1 (np*) and 3A1(pp*) states, though the interaction is smaller than that of unsubstituted pyridine because of raising the pp* state by electron-withdrawing groups. It is proposed that the T1 states of 2-4 have smaller deviation from the planar conformation than the T1 state of unsubstituted pyridine.

DOI： 10.1021/j100155a051

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Chemical Society of Japan  

CIDEP spectra of radicals generated from photoinduced hydrogen abstraction and a-cleavage reactions of several alkyl phenyl ketones were studied. The participation of radical pair mechanism on the spectra was discussed from the magnitude of hyperfine interaction.

DOI： 10.1246/cl.1990.1491

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Nonphosphorescent excited triplet (3pp*) states of photoenols (3E) generated from the intramolecular hydrogen transfer of o-methylacetophenone (OMAP) and related compounds were measured, together with their phosphorescent excited triplet state (3K), by time-resolved ESR techniques at low temperatures. The triplet ESR spectrum with zero-field splitting parameters, |D| = 0.060 and IEI = 0.0025 cm-', clearly different from those of the parent molecules (3K), was assigned to 3E. The observed small ID| value suggests the biradical character of 3E. It was pointed out from the examination of substituent and matrix effects that the ease of photoenol generation clearly depends on the character of the T1 state of the parent molecules and also on the coplanarity of the carbonyl group with the aromatic ring. The presence of water induces a striking change in the character of the T1 state of OMAP; i.e., np* of T1 in nonpolar or absolute ethanol glassy matrices is altered by pp* in 0.5% H2O/ethanol. CIDEP spectra observed from the quenching reaction with methylviologen proved that 3E behaves as an excellent electron donor.

DOI： 10.1021/j100357a015

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Publishing type：Research paper (scientific journal)   Publisher：The Chemical Society of Japan  

Time-resolved ESR spectrum was observed for the triplet enol generated by intramolecular proton transfer in the excited singlet state of o-aminoacetophenone at 77 K. The phase of the polarization and the zero field splitting (ZFS) parameters suggested the formation of the corresponding enol in accordance with previous results. Polarized ESR spectrum due to the excited triplet state was also obtained under laser pulse irradiation to p-aminoacetophenone.

DOI： 10.1246/nikkashi.1989.1463

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Publishing type：Research paper (scientific journal)   Publisher：Institute of Organic Chemistry & Biochemistry  

A time-independent Green function formalism is developed to study the excess energy dependence on the nonradiative decay in the <italic>S</italic>₁ state of benzene. Effects of purely electronic relaxation (internal conversion, IC) and intramolecular vibrational redistribution, IVR, are taken into account at the same time. Model calculations show that the drastic increase in the nonradiative decay rate at around 3 000 cm^-1 excess energy is due to the same onset of both IC and IVR rates. Our theory can explain the difference in rate constant between IVR and IC observed by Moss and Parmenter.

DOI： 10.1135/cccc19881902

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Total pages：xiv, 569 p.   Language：English

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Language：English   Publisher：Elsevier Ltd.  

This chapter describes the characterization of the carbon alloys using the infra-red spectroscopy (IR spectra), the electron paramagnetic resonance (EPR), and the proton magnetic resonance thermal analysis (PMRTA). The broad absorption bands of the IR spectra observed using the diffuse reflectance methods-provide information about the ring size of the aromatic molecules within a sample, and the extent to which these are ordered. The sharp C-H stretching peaks are quantitatively compared with the peaks using the solid-state nuclear magnetic resonance (NMR). Two magnetic resonance methods employed pulse techniques-where the relative hydrogen contents are evaluated as the ratios to carbon contents. PMRTA, which measures the temperature dependence of the signal intensities and the relaxation times of the proton magnetic resonance, provides information about the molecular motion in the heat-treated carbons and in coals. These spectroscopic techniques give information about the composition of the carbon precursors prepared at temperatures below 500-600°C. © 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/B978-008044163-4/50017-6

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Language：English   Publisher：AMER CHEMICAL SOC  

Pulsed electron paramagnetic resonance (EPR) spectroscopy has been applied to elucidate the radical structures of Argonne premium coals and the reaction processes in coal tar pitches (CTP). Using two-dimensional nutation spectroscopy, the main EPR signals around g = 2.00 for the coals were confirmed to be attributed to free radicals rather than spin clusters with higher spin multiplicities. The broad H-1- and C-13-hyperfine spectra of the coals were detected separately by hyperfine sublevel correlation (HYSCORE) spectroscopy. It is concluded that the main coal radicals are pi radicals delocalized in pericondensed aromatic hydrocarbons with more than seven aromatic rings, which are larger than those of the most probable aromatic molecules in coals. HYSCORE spectroscopy, furthermore, helped us to understand the chemical change in the cation radicals in the charge-transfer complexes that accelerate the dehydrogenative polymerization of I-2-treated CTP.

DOI： 10.1021/ef010148j

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Language：English   Publisher：AMER CHEMICAL SOC  

Pulsed electron paramagnetic resonance (EPR) spectroscopy has been applied to elucidate the radical structures of Argonne premium coals and the reaction processes in coal tar pitches (CTP). Using two-dimensional nutation spectroscopy, the main EPR signals around g = 2.00 for the coals were confirmed to be attributed to free radicals rather than spin clusters with higher spin multiplicities. The broad H-1- and C-13-hyperfine spectra of the coals were detected separately by hyperfine sublevel correlation (HYSCORE) spectroscopy. It is concluded that the main coal radicals are pi radicals delocalized in pericondensed aromatic hydrocarbons with more than seven aromatic rings, which are larger than those of the most probable aromatic molecules in coals. HYSCORE spectroscopy, furthermore, helped us to understand the chemical change in the cation radicals in the charge-transfer complexes that accelerate the dehydrogenative polymerization of I-2-treated CTP.

DOI： 10.1021/ef010148j

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DOI： 10.1021/ef010148j

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Grinding a mixture of 3-chlorobiphenyl (BP-Cl) and CaO with or without the addition of quartz was conducted in air by a planetary ball mill to investigate the mechanochemical dechlorination of BP-Cl. The dechlorinating reaction proceeds with an increase in grinding time, and over 99% of BP-Cl is decomposed at 360 min. Washing the ground sample with different solvents results in different products. Addition of quartz to the grinding mixture facilitates dechlorination efficiency, especially in the case of a high weight ratio of BP-Cl to CaO.

DOI： 10.1021/es010638q

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Language：English   Publisher：CHEMICAL SOC JAPAN  

For the first time, we detected paramagnetic products generated during the grinding of 3-chlorobiphenyl (BP-Cl) with calcium oxide (CaO) nanoparticles by a ball mill method, which is one of the promising ways to detoxify hazardous chlorinated organic compounds. Those products were assigned to oxygen-centered aromatic radicals coming from BP-Cl and trapped electrons in oxygen vacancies on the surfaces of the CaO reactants using high-frequency and pulsed electron paramagnetic resonance spectroscopies. The observed good correlation between the dechlorination efficiency and the radical yield suggests that a radical mechanism plays an important role in the destruction of organochlorine compounds. The mechanochemical dechlorination could be interpreted by the following mechanism. First of all, the mechanical stressing induces the electron transfer from O2- sites on the surface of the CaO particle to the organic compounds. The produced organic anion radicals then undergo the effective self-dissociation of a chlorine-carbon bond.

DOI： 10.1246/bcsj.74.2303

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Language：English   Publisher：AMER CHEMICAL SOC  

Grinding a mixture of 3-chlorobiphenyl (BP-Cl) and CaO with or without the addition of quartz was conducted in air by a planetary ball mill to investigate the mechanochemical dechlorination of BP-Cl. The dechlorinating reaction proceeds with an increase in grinding time, and over 99% of BP-Cl is decomposed at 360 min. Washing the ground sample with different solvents results in different products. Addition of quartz to the grinding mixture facilitates dechlorination efficiency, especially in the case of a high weight ratio of BP-Cl to CaO.

DOI： 10.1021/es01038q

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Language：English  

For the first time, we detected paramagnetic products generated during the grinding of 3-chlorobiphenyl (BP-Cl) with calcium oxide (CaO) nanoparticles by a ball mill method, which is one of the promising ways to detoxify hazardous chlorinated organic compounds. Those products were assigned to oxygen-centered aromatic radicals coming from BP-Cl and trapped electrons in oxygen vacancies on the surfaces of the CaO reactants using high-frequency and pulsed electron paramagnetic resonance spectroscopies. The observed good correlation between the dechlorination efficiency and the radical yield suggests that a radical mechanism plays an important role in the destruction of organochlorine compounds. The mechanochemical dechlorination could be interpreted by the following mechanism. First of all, the mechanical stressing induces the electron transfer from O 2- sites on the surface of the CaO particle to the organic compounds. The produced organic anion radicals then undergo the effective self-dissociation of a chlorine-carbon bond.

DOI： 10.1246/bcsj.74.2303

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Copper(II), zinc(II), and nickel(II) complexes with tridentate imino nitroxyl diradicals, [CuCl(bisimpy)(MeOH)]-(PF6) (1), [ZnCl2(bisimpy)] (2), and [NiCl(bisimpy)(H2O)(2)]Cl . 2H(2)O (3) (bisimpy = 2,6-bis(1'-oxyl-4',4',5',5'-tetramethyl-4',5'-dihydro-1'H-imidazol-2'-yl)pyridine), were prepared, and their magnetic properties were studied. In 1, the Cu(II) ion has a square pyramidal coordination geometry, of which the equatorial coordination sites are occupied by three nitrogen atoms from the bisimpy and a chloride ion. The coordination geometry of the Zn(II) ion in 2 can be described as a trigonal bipyramid, with two chloride ions and a bisimpy. In 3, the Ni(II) ion has a distorted octahedral coordination geometry, of which four coordination sites are coordinated by the bisimpy and chloride ion, and two water molecules occupy the remaining cis positions. Magnetic susceptibility and EPR measurements revealed that in 1 and 3 the Cu(II) and Ni(II) ions with imino nitroxyl diraicals were ferromagnetically respectively, and the coupled, with the coupling constants J (H = -2J(ij)SigmaS(i)S(j)) of +165(1) and 109(2) cm(-1), intraligand ferromagnetic interactions in 1-3 were very weak. DFT molecular orbital calculations were performed on the diradical ligand, 1, and 2 to study the spin density distribution before and after coordination to the metal ions.

DOI： 10.1021/ic0102384

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Copper(II), zinc(II), and nickel(II) complexes with tridentate imino nitroxyl diradicals, [CuCl(bisimpy)(MeOH)]-(PF6) (1), [ZnCl2(bisimpy)] (2), and [NiCl(bisimpy)(H2O)(2)]Cl . 2H(2)O (3) (bisimpy = 2,6-bis(1'-oxyl-4',4',5',5'-tetramethyl-4',5'-dihydro-1'H-imidazol-2'-yl)pyridine), were prepared, and their magnetic properties were studied. In 1, the Cu(II) ion has a square pyramidal coordination geometry, of which the equatorial coordination sites are occupied by three nitrogen atoms from the bisimpy and a chloride ion. The coordination geometry of the Zn(II) ion in 2 can be described as a trigonal bipyramid, with two chloride ions and a bisimpy. In 3, the Ni(II) ion has a distorted octahedral coordination geometry, of which four coordination sites are coordinated by the bisimpy and chloride ion, and two water molecules occupy the remaining cis positions. Magnetic susceptibility and EPR measurements revealed that in 1 and 3 the Cu(II) and Ni(II) ions with imino nitroxyl diraicals were ferromagnetically respectively, and the coupled, with the coupling constants J (H = -2J(ij)SigmaS(i)S(j)) of +165(1) and 109(2) cm(-1), intraligand ferromagnetic interactions in 1-3 were very weak. DFT molecular orbital calculations were performed on the diradical ligand, 1, and 2 to study the spin density distribution before and after coordination to the metal ions.

DOI： 10.1021/ic0102384

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Language：English   Publisher：AMER INST PHYSICS  

The lowest excited triplet (T-1) states of diphenylacetylene and several alpha,omega -diphenylpolyynes (DPY) having two, three, four and six triple bonds were studied using continuous wave time-resolved electron paramagnetic resonance (CW-TREPR), pulsed EPR, and phosphorescence spectroscopy. Linear and planar molecular structures in the T-1 states of DPY were suggested from the magnetophotoselection experiments and observation of a strong 0-0 band in the well-resolved phosphorescence spectra. The spin density distributions, which were obtained by electron spin echo envelope modulation measurements and semi-empirical molecular orbital calculations, and the phosphorescence polarization normal to the long axis of molecule for the 0-0 bands suggested that the T-1 states of DPY have a B-3(1u) (pi (x)pi (x)*) electronic configuration. DPY showed an abnormally large \D\ value of the zero-field splitting parameters that increased with increasing molecular size. Such an unusual behavior of the D values is interpreted in terms of the spin-orbit interaction between the T-1 and (3)A(u)(pi (x)pi (y)*) states mainly due to their energy proximity which is probably characteristic of the excited states for the polyynes. The estimated energy gap between the (3)pi (x)pi (y)* and (3)pi (x)pi (x)* states for DPY ranges from 2900 cm(-1) to 1400 cm(-1). There existed a good correlation between the acceleration of the nonradiative decay rate constant from the T1 state and appearance of a ring twisting vibronic band with b(1g) symmetry in the phosphorescence spectra for DPY. Therefore, we concluded that the vibronic interaction between the (3)pi (x)pi (y)* and (3)pi (x)pi (x)* states promoted by the b(1g) vibration leads to a broadening of the potential surface of the T-1 state which results in the fast radiationless decay Co the ground state, (C) 2001 American Institute of Physics.

DOI： 10.1063/1.1331614

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The lowest excited triplet (T-1) states of diphenylacetylene and several alpha,omega -diphenylpolyynes (DPY) having two, three, four and six triple bonds were studied using continuous wave time-resolved electron paramagnetic resonance (CW-TREPR), pulsed EPR, and phosphorescence spectroscopy. Linear and planar molecular structures in the T-1 states of DPY were suggested from the magnetophotoselection experiments and observation of a strong 0-0 band in the well-resolved phosphorescence spectra. The spin density distributions, which were obtained by electron spin echo envelope modulation measurements and semi-empirical molecular orbital calculations, and the phosphorescence polarization normal to the long axis of molecule for the 0-0 bands suggested that the T-1 states of DPY have a B-3(1u) (pi (x)pi (x)*) electronic configuration. DPY showed an abnormally large \D\ value of the zero-field splitting parameters that increased with increasing molecular size. Such an unusual behavior of the D values is interpreted in terms of the spin-orbit interaction between the T-1 and (3)A(u)(pi (x)pi (y)*) states mainly due to their energy proximity which is probably characteristic of the excited states for the polyynes. The estimated energy gap between the (3)pi (x)pi (y)* and (3)pi (x)pi (x)* states for DPY ranges from 2900 cm(-1) to 1400 cm(-1). There existed a good correlation between the acceleration of the nonradiative decay rate constant from the T1 state and appearance of a ring twisting vibronic band with b(1g) symmetry in the phosphorescence spectra for DPY. Therefore, we concluded that the vibronic interaction between the (3)pi (x)pi (y)* and (3)pi (x)pi (x)* states promoted by the b(1g) vibration leads to a broadening of the potential surface of the T-1 state which results in the fast radiationless decay Co the ground state, (C) 2001 American Institute of Physics.

DOI： 10.1063/1.1331614

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Using two-, three- and five-pulse methods, we have measured the electron spin echo envelope modulation (ESEEM) of a stable paramagnetic center existing in a non-doped ladder polymer, in which two polydiacetylenes are conjugated in each repeating unit. A relatively deep modulation effect owing to weak hyperfine interaction with protons was observed. The number of interacting protons was estimated to be a few tens based on the analysis of the modulation amplitude. The interaction with many protons implies that the paramagnetic center in the ladder polydiacetylene also possesses a wavefunction delocalized on several units in the pi -conjugated system like the spin solitons in polyacetylene. (C) 2001 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0038-1098(00)00471-3

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Using two-, three- and five-pulse methods, we have measured the electron spin echo envelope modulation (ESEEM) of a stable paramagnetic center existing in a non-doped ladder polymer, in which two polydiacetylenes are conjugated in each repeating unit. A relatively deep modulation effect owing to weak hyperfine interaction with protons was observed. The number of interacting protons was estimated to be a few tens based on the analysis of the modulation amplitude. The interaction with many protons implies that the paramagnetic center in the ladder polydiacetylene also possesses a wavefunction delocalized on several units in the pi -conjugated system like the spin solitons in polyacetylene. (C) 2001 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0038-1098(00)00471-3

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Language：English   Publisher：SPRINGER-VERLAG BERLIN  

We studied iron-hydrogen (Fe-H) complexes in Si by EPR measurements. Specimens prepared from an n-type FZ-Si crystal (phosphorus concentration: 1X10(16)cm(-3)) were doped with Fe and H by heating in Fe vapor and H-2 gas, respectively. EPR spectra were measured with use of an X-band and a Q-band spectrometer. New EPR absorption spectra were observed at around 2.067 of g-value. We identified them to be due to Fe-H pair from the EPR spectrum, the isotope effect of hydrogen and thermal stability. To explain a peculiar dependence of EPR spectrum on the measurement frequencies (X-band and Q-band), we propose that the H atom in Fe-H pair moves around the Fe atom by tunneling.

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Language：English   Publisher：WILEY-V C H VERLAG GMBH  

DOI： 10.1002/1521-3773(20010903)40:17<3234::AID-ANIE3234>3.0.CO;2-B

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We studied iron-hydrogen (Fe-H) complexes in Si by EPR measurements. Specimens prepared from an n-type FZ-Si crystal (phosphorus concentration: 1X10(16)cm(-3)) were doped with Fe and H by heating in Fe vapor and H-2 gas, respectively. EPR spectra were measured with use of an X-band and a Q-band spectrometer. New EPR absorption spectra were observed at around 2.067 of g-value. We identified them to be due to Fe-H pair from the EPR spectrum, the isotope effect of hydrogen and thermal stability. To explain a peculiar dependence of EPR spectrum on the measurement frequencies (X-band and Q-band), we propose that the H atom in Fe-H pair moves around the Fe atom by tunneling.

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Language：English   Publisher：WILEY-V C H VERLAG GMBH  

DOI： 10.1002/1521-3773(20010903)40:17<3234::AID-ANIE3234>3.0.CO;2-B

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Dangling bond (DB) defects in unhydrogenated microcrystalline silicon (mu c-Si) prepared by rf sputtering have been studied. Raman spectra and x-ray diffraction indicate that the mu c-Si fraction has been formed at the Ar sputtering pressure higher than 26.6 Pa while only amorphous silicon (a-Si) has been produced at the lower pressure. The electron paramagnetic resonance (EPR) spectrum in the mu c-Si film is broad and unsymmetrical with the average g value of g=2.006 compared with that of a-Si (g=2.0055). The X- and Q-band EPR measurements suggest that the line shape is mainly governed by the inhomogeneous broadening due to the g anisotropy, indicating relatively large distribution of the structure of the DB defects. (C) 2000 American Institute of Physics. [S0021-8979(00)06712-8].

DOI： 10.1063/1.373875

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Dangling bond (DB) defects in unhydrogenated microcrystalline silicon (mu c-Si) prepared by rf sputtering have been studied. Raman spectra and x-ray diffraction indicate that the mu c-Si fraction has been formed at the Ar sputtering pressure higher than 26.6 Pa while only amorphous silicon (a-Si) has been produced at the lower pressure. The electron paramagnetic resonance (EPR) spectrum in the mu c-Si film is broad and unsymmetrical with the average g value of g=2.006 compared with that of a-Si (g=2.0055). The X- and Q-band EPR measurements suggest that the line shape is mainly governed by the inhomogeneous broadening due to the g anisotropy, indicating relatively large distribution of the structure of the DB defects. (C) 2000 American Institute of Physics. [S0021-8979(00)06712-8].

DOI： 10.1063/1.373875

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We report electron paramagnetic resonance (EPR) studies in dangling bond (DB) defects in the hydrogenated microcrystalline silicon (mu c-Si:H) film prepared by a plasma enhanced chemical vapor deposition (PECVD), unhydrogenated microcrystalline silicon (mu c-Si) film prepared by RF sputtering, and mu c-Si embedded in SiO2 film formed by co-sputtering followed by annealing. Multi-band EPR measurements showed that their line widths originate primarily from a distribution of the g-values. We have detected a signal at g = 2.006 in the microcrystalline fraction of the mu c-Si, mu c-Si:H and mu c-Si embedded SiO2 films. The signal has a greater width than the DB signal in amorphous silicon (a-Si), indicating a larger distribution of g-values of the defects in the microcrystalline material. The DB signal in the mu c-Si embedded in SiO2 was reproduced by the computer simulation taking into account the distribution of the g-values. (C) 2000 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0022-3093(00)00027-2

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We report electron paramagnetic resonance (EPR) studies in dangling bond (DB) defects in the hydrogenated microcrystalline silicon (mu c-Si:H) film prepared by a plasma enhanced chemical vapor deposition (PECVD), unhydrogenated microcrystalline silicon (mu c-Si) film prepared by RF sputtering, and mu c-Si embedded in SiO2 film formed by co-sputtering followed by annealing. Multi-band EPR measurements showed that their line widths originate primarily from a distribution of the g-values. We have detected a signal at g = 2.006 in the microcrystalline fraction of the mu c-Si, mu c-Si:H and mu c-Si embedded SiO2 films. The signal has a greater width than the DB signal in amorphous silicon (a-Si), indicating a larger distribution of g-values of the defects in the microcrystalline material. The DB signal in the mu c-Si embedded in SiO2 was reproduced by the computer simulation taking into account the distribution of the g-values. (C) 2000 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0022-3093(00)00027-2

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Language：English   Publisher：JAPAN J APPLIED PHYSICS  

We have examined Raman scattering, X-ray diffraction, electron paramagnetic resonance (EPR) spectra and the conductivity of nitrogen-doped hydrogenated microcrystalline silicon. The EPR signals due to conduction electrons have been observed in the doped films, except for highly doped samples that have no microcrystalline fraction. The result indicates that the doped nitrogen atom acts as an electron donor in the microcrystalline silicon. The temperature dependence of the conductivity clarify that the activation energy depends on the doping level. The influence of the doping level on the conductivity can be interpreted in terms:of the balance of the effective electron donation and the decrease of carrier mobility due to a decrease of the microcrystalline phase volume ratio. At temperatures lower than approximately 180 K, the conductivity shows little variation. This is explained using a model of the hopping conduction, in terms of defect states for all samples.

DOI： 10.1143/JJAP.39.31

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Language：English   Publisher：JAPAN J APPLIED PHYSICS  

We have examined Raman scattering, X-ray diffraction, electron paramagnetic resonance (EPR) spectra and the conductivity of nitrogen-doped hydrogenated microcrystalline silicon. The EPR signals due to conduction electrons have been observed in the doped films, except for highly doped samples that have no microcrystalline fraction. The result indicates that the doped nitrogen atom acts as an electron donor in the microcrystalline silicon. The temperature dependence of the conductivity clarify that the activation energy depends on the doping level. The influence of the doping level on the conductivity can be interpreted in terms:of the balance of the effective electron donation and the decrease of carrier mobility due to a decrease of the microcrystalline phase volume ratio. At temperatures lower than approximately 180 K, the conductivity shows little variation. This is explained using a model of the hopping conduction, in terms of defect states for all samples.

DOI： 10.1143/JJAP.39.31

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Iodine introduced into coal tar pitch (CTP) can drastically alter its reology and carbonization behavior. Here, the mechanism of interaction between iodine and CTP has been investigated by using various spectroscopic methods such as I-127-NMR, EPR and FT-IR. It is shown that some iodine molecules infiltrated into the CTP and form charge transfer complexes with the relative large aromatic components of the CTP. Hyperfine sublevel correlation spectroscopy (HYSCORE) revealed the molecular size of cation radicals, which contain more than ten benzene rings, and the location of iodine anion that is incorporated at ca. 0.3 nm from the aromatic cation radicals. The elemental H/C ratio decreased and the viscosity of CTP increased with the density of the charge-transfer complexes, which was also increased by the iodine treatment. These results strongly suggest that dehydrogenative polymerization of CTP occurs during the iodine treatment. The cation radicals in the charge-transfer complexes accelerate the dehydrogenative polymerization and result in a high carbon yield. (C) 2000 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0008-6223(00)00022-1

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Iodine introduced into coal tar pitch (CTP) can drastically alter its reology and carbonization behavior. Here, the mechanism of interaction between iodine and CTP has been investigated by using various spectroscopic methods such as I-127-NMR, EPR and FT-IR. It is shown that some iodine molecules infiltrated into the CTP and form charge transfer complexes with the relative large aromatic components of the CTP. Hyperfine sublevel correlation spectroscopy (HYSCORE) revealed the molecular size of cation radicals, which contain more than ten benzene rings, and the location of iodine anion that is incorporated at ca. 0.3 nm from the aromatic cation radicals. The elemental H/C ratio decreased and the viscosity of CTP increased with the density of the charge-transfer complexes, which was also increased by the iodine treatment. These results strongly suggest that dehydrogenative polymerization of CTP occurs during the iodine treatment. The cation radicals in the charge-transfer complexes accelerate the dehydrogenative polymerization and result in a high carbon yield. (C) 2000 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0008-6223(00)00022-1

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Reactions of [Fe-II(CN)(2)(bpy)(2)] and [Fe-III(CN)(2)(bpy)(2)](PF6) with [Cu-II(bpy)(CH3OH)(2)](PF6)(2) in methanol yielded cyanide-bridged cyclic tetranuclear complexes of [(Fe2Cu2II)-Cu-II(mu-CN)(4)(bpy)(6)](PF6)(4). 2H(2)O . 4CHCl(3) (1) and [Fe-2(III)-Cu-2(II) (mu-CN)(4)(bpy)(6)](PF6)(6) . 4CH(3)CN . 2CNCl(3) (2), respectively. Zn the squares of 1 and 2, the Fe2+/3+ (low-spin) and Cu2+ ions are alternately bridged by the cyanide ions, the carbon atoms of which coordinate to the iron ions. Variable-temperature magnetic susceptibility studies of complexes revealed that the Cu2+ ions in 1 are magnetically isolated. In the square of 2, the adjacent Fe3+ and Cu2+ ions were ferromagnetically coupled through the cyanide bridges with a J(1) value of +6.3(1) cm(-1) and the weaker antiferromagnetic interactions between the orthogonal Fe3+... Fe3+ and Cu2+...Cu2+ pairs are operative (J(2) = -3.1(1) cm(-1)). The propagation of the ferromagnetic interaction in 2 can be understood by the orthogonal magnetic orbitals of the low-spin Fe3+ (d pi) and Cu2+ (d sigma) ions. Cyclic voltammograms of the squares have been recorded and discussed. Crystal data for 1: triclinic space group P (1) over bar, a = 14.491(4) Angstrom, b = 15.312(4) Angstrom, c = 12.959(3) Angstrom, alpha = 91.38(2)degrees , beta = 109.56(2)degrees, gamma = 65.41(2)degrees, Z = 1. Crystal data for 2: triclinic space group P (1) over bar, a = 14.472(9) Angstrom, b = 15.310(6) Angstrom, c = 12.523(5) Angstrom, alpha 102.58(3)degrees beta = 107.19(4)degrees, gamma = 75.08(4)degrees, Z = 1.

DOI： 10.1021/ic990617l

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Reactions of [Fe-II(CN)(2)(bpy)(2)] and [Fe-III(CN)(2)(bpy)(2)](PF6) with [Cu-II(bpy)(CH3OH)(2)](PF6)(2) in methanol yielded cyanide-bridged cyclic tetranuclear complexes of [(Fe2Cu2II)-Cu-II(mu-CN)(4)(bpy)(6)](PF6)(4). 2H(2)O . 4CHCl(3) (1) and [Fe-2(III)-Cu-2(II) (mu-CN)(4)(bpy)(6)](PF6)(6) . 4CH(3)CN . 2CNCl(3) (2), respectively. Zn the squares of 1 and 2, the Fe2+/3+ (low-spin) and Cu2+ ions are alternately bridged by the cyanide ions, the carbon atoms of which coordinate to the iron ions. Variable-temperature magnetic susceptibility studies of complexes revealed that the Cu2+ ions in 1 are magnetically isolated. In the square of 2, the adjacent Fe3+ and Cu2+ ions were ferromagnetically coupled through the cyanide bridges with a J(1) value of +6.3(1) cm(-1) and the weaker antiferromagnetic interactions between the orthogonal Fe3+... Fe3+ and Cu2+...Cu2+ pairs are operative (J(2) = -3.1(1) cm(-1)). The propagation of the ferromagnetic interaction in 2 can be understood by the orthogonal magnetic orbitals of the low-spin Fe3+ (d pi) and Cu2+ (d sigma) ions. Cyclic voltammograms of the squares have been recorded and discussed. Crystal data for 1: triclinic space group P (1) over bar, a = 14.491(4) Angstrom, b = 15.312(4) Angstrom, c = 12.959(3) Angstrom, alpha = 91.38(2)degrees , beta = 109.56(2)degrees, gamma = 65.41(2)degrees, Z = 1. Crystal data for 2: triclinic space group P (1) over bar, a = 14.472(9) Angstrom, b = 15.310(6) Angstrom, c = 12.523(5) Angstrom, alpha 102.58(3)degrees beta = 107.19(4)degrees, gamma = 75.08(4)degrees, Z = 1.

DOI： 10.1021/ic990617l

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We have measured the excitation spectra for tropolone-OH in durene single crystal and tropolone-OD in deuterated durene using a time-resolved electron paramagnetic resonance (TREPR) detection method that makes possible to separate the signals due to magnetically different sites. The tunneling doublet with 3 cm(-1) was observed in the sharp zero-phonon line. The small splitting indicates that the crystal field increases the barrier of double-minimum potential for the proton tunneling in the S-1 state. Moderately asymmetric potentials of the S-0 and S-1 states, where the energetic imbalance between two wells in the S-1 state potential is opposite the S-0 state potential, reasonably explained the observed unusual intensity ratio of the tunneling doublet (0(1)(+) &lt; 0(1)(-)). A well-resolved progression of a phonon band with a 15 cm(-1) separation was also obtained in durene crystal at very low temperature. From a Franck-Condon analysis of the relative intensity of the phonon band, it was clarified that the stable configuration of the excited state tropolone in durene differed from that of the ground state. (C) 1999 American Institute of Physics. [S0021-9606(99)00439-0].

DOI： 10.1063/1.479980

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We have measured the excitation spectra for tropolone-OH in durene single crystal and tropolone-OD in deuterated durene using a time-resolved electron paramagnetic resonance (TREPR) detection method that makes possible to separate the signals due to magnetically different sites. The tunneling doublet with 3 cm(-1) was observed in the sharp zero-phonon line. The small splitting indicates that the crystal field increases the barrier of double-minimum potential for the proton tunneling in the S-1 state. Moderately asymmetric potentials of the S-0 and S-1 states, where the energetic imbalance between two wells in the S-1 state potential is opposite the S-0 state potential, reasonably explained the observed unusual intensity ratio of the tunneling doublet (0(1)(+) &lt; 0(1)(-)). A well-resolved progression of a phonon band with a 15 cm(-1) separation was also obtained in durene crystal at very low temperature. From a Franck-Condon analysis of the relative intensity of the phonon band, it was clarified that the stable configuration of the excited state tropolone in durene differed from that of the ground state. (C) 1999 American Institute of Physics. [S0021-9606(99)00439-0].

DOI： 10.1063/1.479980

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Language：English   Publisher：Elsevier  

Unusually large D values of zero-field splitting parameters were observed for 1,6-diphenylhexatriyne (D=0.396 cm-1) and 1,8-diphenyloctatetrayne (D=0.533 cm-1) by using time-resolved EPR (TREPR) spectroscopy. The lowest excited triplet (T1) states of these diphenylpolyynes were assigned to 3B1u(3πxπ * x) in character from the degree of the polarization of phosphorescence. It has been concluded that the present diphenylpolyynes have a linear planar structure in the T1 states, although the TREPR and phosphorescence spectra indicate interactions between the T1(3πxπ* x) and Tn(3πxπ* y) states through spin-orbit and vibronic interactions.

DOI： 10.1016/S0009-2614(99)00189-X

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Unusually large \D\ values of zero-field splitting parameters were observed for 1,6-diphenylhexatriyne (\D\ = 0.396 cm(-1)) and 1,8-diphenyloctatetrayne (\D\ = 0.533 cm(-1)) by using time-resolved EPR (TREPR) spectroscopy. The lowest excited triplet (T-1) states of these diphenylpolyynes were assigned to B-3(1u)((3)pi(x)pi(x)(*)) in character from the degree of the polarization of phosphorescence. It has been concluded that the present diphenylpolyynes have a linear planar structure in the T-1 states, although the TREPR and phosphorescence spectra indicate interactions between the T-1((3)pi(x)pi(x)(*)) and T-n((3)pi(x)pi(y)(*)) states through spin-orbit and vibronic interactions. (C) 1999 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0009-2614(99)00189-X

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Language：English   Publisher：TAYLOR & FRANCIS LTD  

Employing X- and Q-band time-resolved EPR and pulsed EPR techniques, we have investigated effects of twist conformation on the electronic structures and magnetic properties of the lowest excited triplet states of alkyl phenyl ketones. The conformational variation due to steric hindrance of a bulky substituent on the alpha-position drastically leads to a decrease of the zero-field splitting constant of \D\ and an increase of the energy gap between (3)n pi* and (3)pi pi* states. Hydrogen bonding with H2O destabilized significantly the (3)n pi* state and switched the T-1 state to the (3)pi pi* state. t-Butyl phenyl ketone gave unusually broad EPR spectra in rigid glassy matrices. The multifrequency and pulsed EPR measurements clarified that the inhomogeneously broadening spectra were ascribable to the distribution of the dihedral angle about a twist conformation. Asymmetric distribution of the ZFS parameters was interpreted in terms of the perturbation of spin-orbit interactions to the spin sublevels.

DOI： 10.1080/002689799165198

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Language：English   Publisher：TAYLOR & FRANCIS LTD  

Employing X- and Q-band time-resolved EPR and pulsed EPR techniques, we have investigated effects of twist conformation on the electronic structures and magnetic properties of the lowest excited triplet states of alkyl phenyl ketones. The conformational variation due to steric hindrance of a bulky substituent on the alpha-position drastically leads to a decrease of the zero-field splitting constant of \D\ and an increase of the energy gap between (3)n pi* and (3)pi pi* states. Hydrogen bonding with H2O destabilized significantly the (3)n pi* state and switched the T-1 state to the (3)pi pi* state. t-Butyl phenyl ketone gave unusually broad EPR spectra in rigid glassy matrices. The multifrequency and pulsed EPR measurements clarified that the inhomogeneously broadening spectra were ascribable to the distribution of the dihedral angle about a twist conformation. Asymmetric distribution of the ZFS parameters was interpreted in terms of the perturbation of spin-orbit interactions to the spin sublevels.

DOI： 10.1080/002689799165198

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DOI： 10.3775/jie.78.980

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Authorship：Lead author,　Corresponding author  

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DOI： 10.3775/jie.78.980

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Language：English   Publisher：AMER CHEMICAL SOC  

Hyperfine sublevel correlation spectroscopy (HYSCORE) spectra have been measured for the radicals in eight well-characterized Argonne Premium coals and their model compounds. The broad H-1 and C-13 hyperfine spectra of all coals were detected at room temperature. The hyperfine structure was analyzed by the comparison with model radicals and semiempirical molecular orbital calculations. The main coal radicals are considered as two-dimensionally condensed pi radicals with more than seven aromatic rings. The C-13/H-1 ratio of the hyperfine spectra increases with coal rank, suggesting a new index of coal rank.

DOI： 10.1021/ef980130h

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The short-lived T-1 state of 1,4-diphenylbutadiyne (DPB) has been investigated in various glassy matrices at low temperatures using time-resolved EPR and pulsed EPR methods. Zero-field splitting parameters of D = -0.250 cm(-1) and E = +0.018 cm(-1) were determined. The negative D value was verified from the M-S dependence of the ENDOR frequencies. The hyperfine splitting constants of ring protons were obtained from the electron spin-echo envelope modulation with three-pulse stimulated echo. The spin density distribution on the phenyl groups was estimated from the analysis of the hyperfine splittings at each of the canonical orientations. The moderate spin densities on the phenyl rings indicated that the T-1 state was (3)pi(x)pi(x)* in electronic character. The origin of the large negative D value of DPB has been discussed in terms of the spin-orbit interaction between the close lying (3)pi(x)pi(x)* and (3)pi(x)pi(y)* states.

DOI： 10.1021/jp9812740

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The short-lived T-1 state of 1,4-diphenylbutadiyne (DPB) has been investigated in various glassy matrices at low temperatures using time-resolved EPR and pulsed EPR methods. Zero-field splitting parameters of D = -0.250 cm(-1) and E = +0.018 cm(-1) were determined. The negative D value was verified from the M-S dependence of the ENDOR frequencies. The hyperfine splitting constants of ring protons were obtained from the electron spin-echo envelope modulation with three-pulse stimulated echo. The spin density distribution on the phenyl groups was estimated from the analysis of the hyperfine splittings at each of the canonical orientations. The moderate spin densities on the phenyl rings indicated that the T-1 state was (3)pi(x)pi(x)* in electronic character. The origin of the large negative D value of DPB has been discussed in terms of the spin-orbit interaction between the close lying (3)pi(x)pi(x)* and (3)pi(x)pi(y)* states.

DOI： 10.1021/jp9812740

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Rare earth ion (Er3+, Eu3+ and Sm3+)-doped alumina films have been prepared by the sol-gel method, using AlCl3-derived alumina sol. The effects of dopant concentration and treatment temperatures on the photo-properties of absorption and emission have been examined for the doped films. These sol-gel-derived alumina matrices gave a high-dopant concentration (~15 mol% per alumina).

DOI： 10.1016/S0009-2614(98)00132-8

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Rare earth ion (Er3+, Eu3+ and Sm3+)-doped alumina films have been prepared by the sol-gel method, using AlCl3-derived alumina sol. The effects of dopant concentration and treatment temperatures on the photo-properties of absorption and emission have been examined for the doped films. These sol-gel-derived alumina matrices gave a high-dopant concentration(similar to 15 mol% per alumina). (C) 1998 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0009-2614(98)00132-8

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Language：English   Publisher：ROYAL SOC CHEMISTRY  

Time-resolved EPR measurements and semi-empirical MO calculations have been carried out to clarify the electronic structure of the T-1 state of nonphosphorescent tropolone. The observed zero-field splitting parameters indicate that the T-1 state has a pure pi pi* character and the energy order among the spin sublevels was T-Y (in-plane) &gt; T-X (in-plane) &gt; 0 &gt; T-Z (out-of-plane), which is the same as tropone for a parent molecule. However, the principal X-axis slightly turns out of the carbonyl bond direction so that the intersystem crossing from the S-1 state to the T-Y sublevel becomes more active. The spin densities obtained from hyperfine splittings of protons and MO calculation of AM1 method show an asymmetric distribution of unpaired pi-electrons over two oxygens as well as the seven-membered ring. This unbalanced distribution makes the deviation of the X-axis from the carbonyl bond clear. We found two sites that can exchange each other by intramolecular proton transfer in a durene single crystal.

DOI： 10.1039/a708678d

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Language：English   Publisher：ROYAL SOC CHEMISTRY  

Time-resolved EPR measurements and semi-empirical MO calculations have been carried out to clarify the electronic structure of the T-1 state of nonphosphorescent tropolone. The observed zero-field splitting parameters indicate that the T-1 state has a pure pi pi* character and the energy order among the spin sublevels was T-Y (in-plane) &gt; T-X (in-plane) &gt; 0 &gt; T-Z (out-of-plane), which is the same as tropone for a parent molecule. However, the principal X-axis slightly turns out of the carbonyl bond direction so that the intersystem crossing from the S-1 state to the T-Y sublevel becomes more active. The spin densities obtained from hyperfine splittings of protons and MO calculation of AM1 method show an asymmetric distribution of unpaired pi-electrons over two oxygens as well as the seven-membered ring. This unbalanced distribution makes the deviation of the X-axis from the carbonyl bond clear. We found two sites that can exchange each other by intramolecular proton transfer in a durene single crystal.

DOI： 10.1039/a708678d

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Language：English   Publisher：KLUWER ACADEMIC PUBL  

DOI： 10.1023/A:1006517219037

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DOI： 10.1023/A:1006517219037

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Time-resolved electron paramagnetic resonance experiments on the short-lived Ti state of nenphosphorescent tropone were carried out using mixed crystals. Well-resolved hyperfine splittings due to allowed and forbidden transitions were observed at principal axes of the zero-field tenser. The spin density distribution, C-H bond angles, and the sign of the D value were deduced from the hyperfine spectra. It has been concluded that the T-1 state of tropone mainly has a (3) pi pi* configuration and holds its molecular structure of C-2v symmetry. The experiments and molecular orbital calculations indicate that the large Franck-Condon factor between the T-1 and the So states arises from the change of the potential surfaces due to the antibonding character of the pi* orbital at the C-4-C-5 bond in the T-1 state.

DOI： 10.1021/jp9721154

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DOI： 10.1021/jp9721154

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Publisher：American Physical Society (APS)  

DOI： 10.1103/PhysRevB.57.1607

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Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.57.1607/fulltext

Publisher：American Physical Society (APS)  

DOI： 10.1103/PhysRevB.57.1607

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Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.57.1607/fulltext

DOI： 10.1021/ef980053q

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DOI： 10.1021/ef980130h

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DOI： 10.1021/ef980053q

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Language：English   Publisher：American Chemical Society  

Phosphorescence and TREPR spectra have been measured for 2-methyl-1,4-naphthoquinone (MNQ), 2,3-dimethyl-1,4-naphthoquinone (DMNQ), and 2-methoxynaphthoquinone (MeONQ) in several matrices at low temperatures. The |D| value of ZFS parameter decreases with increasing the electron-donating character of the substituent group. For MNQ, the T1 state is clearly assigned to be 3nπ* in character. The broad phosphorescence spectra and minor effects of the matrix polarity on the ZFS parameters lead to the conclusion that the character of the T1 states are mainly 3ππ* in DMNQ and MeONQ. The T1 states of the present naphthoquinone derivatives have more or less mixed character of the 3nπ* and 3ππ* states.

DOI： 10.1021/jp971818i

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Language：English   Publisher：American Chemical Society  

Phosphorescence and TREPR spectra have been measured for 2-methyl-1,4-naphthoquinone (MNQ), 2,3-dimethyl-1,4-naphthoquinone (DMNQ), and 2-methoxynaphthoquinone (MeONQ) in several matrices at low temperatures. The |D| value of ZFS parameter decreases with increasing the electron-donating character of the substituent group. For MNQ, the T1 state is clearly assigned to be 3nπ* in character. The broad phosphorescence spectra and minor effects of the matrix polarity on the ZFS parameters lead to the conclusion that the character of the T1 states are mainly 3ππ* in DMNQ and MeONQ. The T1 states of the present naphthoquinone derivatives have more or less mixed character of the 3nπ* and 3ππ* states.

DOI： 10.1021/jp971818i

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An orthogonal arrangement of imino nitroxide ligands in Cu-I and Ag-I complexes results in propagation of an intramolecular ferromagnetic interaction between the coordinated imino nitroxides through these diamagnetic ions. Reaction of [Cu-I(CH3CN)(4)](PF6) and Ag-I(PF6) with imino nitroxides in ethanol solution gave [Cu-I(immepy)(2)-(PF6) (1) and [Ag-I(impy)(2)](PF6) (2), respectively (immepy 2-(2-(6-methylpyridyl))-4,4,5,5-tetramethyl-4,5-dihydro-1H imidazolyl-l-oxy and impy 2-(2-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxy). Complex 1 crystallizes in the orthorhombic space group Pba2, which has a unit cell with a 11.251(2) Angstrom, b = 14.745(3) Angstrom, c = 9.747(2) Angstrom, V = 1617.0(5) Angstrom(3), and Z = 2. Refinement with 991 reflections observed [\I-0\ &gt; 3 sigma(I-0)] gave R = 0.044 (R-w = 0.053). In 1, imino nitroxides coordinate to the Cu-I ions in a tetrahedral fashion, the dihedral angle between coordinating imino nitroxides being 88.7 degrees. Magnetic susceptibility measurement for 1 shows typical triplet-singlet behavior with strong ferromagnetic interactions (J = 55.1(6) cm(-1) with g = 2.0; H = -JS(1).S-2) The UV-visible absorption spectrum of 1 shows strong bands at 454 and 766 nm assignable to charge-transfer bands from the Cu ion to the ligand NLUMO and SOMO, respectively. The pi-back-donation to the SOMO induces the spin on the Cu ion and results in the strong ferromagnetic interaction. Complex 2 crystallizes in the orthorhombic space group P2(1)cn which has a unit cell with a = 10.535(6) Angstrom, b = 31.295(3) Angstrom, c 8.921(4) Angstrom, V = 2941(1) Angstrom(3), and Z = 4. Refinement with 1882 reflections [\I-0\ &gt; 3 sigma(I-0)] gave R = 0.058 (R-w = 0.074). Ln 2, the four coordination sites of the Ag-I ion were completed with two imino nitroxides and the dihedral angle between the imino nitroxides is 79.2 degrees. The EPR spectrum of a frozen ethanol solution of 2 shows a typical triplet signal with zero field splitting (\D\ = 0.043 cm(-1) and \E\ = 0.014 cm(-1)). Curie plots for the rim = 2 signal below 80 K gave a positive Weiss constant (theta = 4 K), suggesting an intramolecular ferromagnetic interaction in 2.

DOI： 10.1021/ic960939e

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Language：English   Publisher：AMER CHEMICAL SOC  

An orthogonal arrangement of imino nitroxide ligands in Cu-I and Ag-I complexes results in propagation of an intramolecular ferromagnetic interaction between the coordinated imino nitroxides through these diamagnetic ions. Reaction of [Cu-I(CH3CN)(4)](PF6) and Ag-I(PF6) with imino nitroxides in ethanol solution gave [Cu-I(immepy)(2)-(PF6) (1) and [Ag-I(impy)(2)](PF6) (2), respectively (immepy 2-(2-(6-methylpyridyl))-4,4,5,5-tetramethyl-4,5-dihydro-1H imidazolyl-l-oxy and impy 2-(2-pyridyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazolyl-1-oxy). Complex 1 crystallizes in the orthorhombic space group Pba2, which has a unit cell with a 11.251(2) Angstrom, b = 14.745(3) Angstrom, c = 9.747(2) Angstrom, V = 1617.0(5) Angstrom(3), and Z = 2. Refinement with 991 reflections observed [\I-0\ &gt; 3 sigma(I-0)] gave R = 0.044 (R-w = 0.053). In 1, imino nitroxides coordinate to the Cu-I ions in a tetrahedral fashion, the dihedral angle between coordinating imino nitroxides being 88.7 degrees. Magnetic susceptibility measurement for 1 shows typical triplet-singlet behavior with strong ferromagnetic interactions (J = 55.1(6) cm(-1) with g = 2.0; H = -JS(1).S-2) The UV-visible absorption spectrum of 1 shows strong bands at 454 and 766 nm assignable to charge-transfer bands from the Cu ion to the ligand NLUMO and SOMO, respectively. The pi-back-donation to the SOMO induces the spin on the Cu ion and results in the strong ferromagnetic interaction. Complex 2 crystallizes in the orthorhombic space group P2(1)cn which has a unit cell with a = 10.535(6) Angstrom, b = 31.295(3) Angstrom, c 8.921(4) Angstrom, V = 2941(1) Angstrom(3), and Z = 4. Refinement with 1882 reflections [\I-0\ &gt; 3 sigma(I-0)] gave R = 0.058 (R-w = 0.074). Ln 2, the four coordination sites of the Ag-I ion were completed with two imino nitroxides and the dihedral angle between the imino nitroxides is 79.2 degrees. The EPR spectrum of a frozen ethanol solution of 2 shows a typical triplet signal with zero field splitting (\D\ = 0.043 cm(-1) and \E\ = 0.014 cm(-1)). Curie plots for the rim = 2 signal below 80 K gave a positive Weiss constant (theta = 4 K), suggesting an intramolecular ferromagnetic interaction in 2.

DOI： 10.1021/ic960939e

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Language：English   Publisher：AMER CHEMICAL SOC  

Time-resolved EPR and phosphorescence spectra have been observed for the lowest excited triplet states of 4-nitropyridine N-oxide and its alkyl derivatives. It has been shown that the ratio of the zero-field-splitting (zfs) parameters reflects the molecular geometry: the \E/D\ value decreases with increasing the twisting angle of the nitro group from the molecular plane. Protic solvents induce significant changes in the zfs parameters and the population ratio of the triplet sublevels. The results are discussed in terms of formation of the hydrogen bonding complex at the N-oxide oxygen atom.

DOI： 10.1021/j100008a009

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Language：English   Publisher：AMER CHEMICAL SOC  

Time-resolved EPR and phosphorescence spectra have been observed for the lowest excited triplet states of 4-nitropyridine N-oxide and its alkyl derivatives. It has been shown that the ratio of the zero-field-splitting (zfs) parameters reflects the molecular geometry: the \E/D\ value decreases with increasing the twisting angle of the nitro group from the molecular plane. Protic solvents induce significant changes in the zfs parameters and the population ratio of the triplet sublevels. The results are discussed in terms of formation of the hydrogen bonding complex at the N-oxide oxygen atom.

DOI： 10.1021/j100008a009

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Language：English   Publisher：GORDON BREACH SCI PUBL LTD  

Orthogonal arrangement of iminonitroxides in [Cu-I(immepy)(2)](PF6) (1) and [Ag-I(impy)(2)](PF6) (2) results in propagation on intramolecular ferromagnetic interaction between coordinating iminonitroxides through these diamagnetic ion. In 1, iminonitroxides coordinate to the Cu-I ion in a tetrahedral fashion, the dihedral angle between coordinating iminonitroxides being 88.7 degrees. Magnetic susceptibility and epr measurements for 1 show the typical ferromagneic behavior with large zero field splitting (2J = 91(1) cm(-1) (H = -2JS(1) . S-2); D = 3.62 cm(-1)). In 2, the four coordination sites of Ag-I ion were completed with two iminonitroxides and the dihedral angle between the iminonitroxides is 79.2 degrees. Temperature dependence of teh epr spectra for frozen ethanol solution of 2 shows that the intramolecular mangetic interaction between radicals is ferromagnetic (theta = 4 K).

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Language：English   Publisher：GORDON BREACH SCI PUBL LTD  

Orthogonal arrangement of iminonitroxides in [Cu-I(immepy)(2)](PF6) (1) and [Ag-I(impy)(2)](PF6) (2) results in propagation on intramolecular ferromagnetic interaction between coordinating iminonitroxides through these diamagnetic ion. In 1, iminonitroxides coordinate to the Cu-I ion in a tetrahedral fashion, the dihedral angle between coordinating iminonitroxides being 88.7 degrees. Magnetic susceptibility and epr measurements for 1 show the typical ferromagneic behavior with large zero field splitting (2J = 91(1) cm(-1) (H = -2JS(1) . S-2); D = 3.62 cm(-1)). In 2, the four coordination sites of Ag-I ion were completed with two iminonitroxides and the dihedral angle between the iminonitroxides is 79.2 degrees. Temperature dependence of teh epr spectra for frozen ethanol solution of 2 shows that the intramolecular mangetic interaction between radicals is ferromagnetic (theta = 4 K).

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Transient triplet EPR spectra of two types of spirans, spiro[9,10-dihydro-9-oxoanthracene-10,2'-benz[f]indan] and spiro[9,10-dihydro-9-oxoanthracene-10,2'-3H-phenalene],were measured in a glassy matrix at 77 K. Spin polarization conservation during the intramolecular triplet-triplet energy-transfer process was observed. The results clearly indicate that spin orientation is conserved in the molecular frame in the presence of an external magnetic field and that the high-field approximation cannot explain the spin polarization pattern observed in the X-band EPR spectra. The results contribute to the understanding of the relaxation processes of the excited states.

DOI： 10.1021/ja00091a042

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DOI： 10.1021/ja00091a042

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Language：English   Publisher：AMER CHEMICAL SOC  

The T1 states of nonphosphorescent 2,3-benzotropone and phosphorescent 4,5-benzotropone were studied by a time-resolved EPR method. For 2,3-benzotropone, the observed magnetic parameters and the decay rate (the average decay rate 1.1 x 10(5) s-1 at 4.2 K) are very similar to those of the parent tropone. On the other hand, 4,5-benzotropone has different magnetic properties and a much slower radiationless decay rate (&lt;30 s-1) than tropone. The mechanism of the fast radiationless transition between the T1 and S0 states of tropone has been discussed.

DOI： 10.1021/j100104a008

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Language：English   Publisher：AMER CHEMICAL SOC  

The T1 states of nonphosphorescent 2,3-benzotropone and phosphorescent 4,5-benzotropone were studied by a time-resolved EPR method. For 2,3-benzotropone, the observed magnetic parameters and the decay rate (the average decay rate 1.1 x 10(5) s-1 at 4.2 K) are very similar to those of the parent tropone. On the other hand, 4,5-benzotropone has different magnetic properties and a much slower radiationless decay rate (&lt;30 s-1) than tropone. The mechanism of the fast radiationless transition between the T1 and S0 states of tropone has been discussed.

DOI： 10.1021/j100104a008

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Language：English   Publishing type：Rapid communication, short report, research note, etc. (scientific journal)   Publisher：AMER CHEMICAL SOC  

The magnetic property and decay kinetics of the nonphosphorescent triplet (T1) state of tropone in glassy matrices have been studied by employing the time-resolved EPR (TREPR) method with excimer and dye laser excitations. The T1 state was assigned to be nearly pure 3-pi-pi* in character from the small zero-field splitting (zfs) parameters (\D\ = 0.077 cm-1 and \E\ = 0.011 cm-1 in a toluene glassy matrix) and their small dependency on the matrix polarity. The directions of the principal axes of the zfs tensor were determined by magnetophotoselection experiments with two colors of lasers. It was found that the T1(pi-pi*) state of tropone has very short lifetime; the average rate constant from the zero-field spin sublevels is 2 x 10(5) s-1.

DOI： 10.1021/j100172a003

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Language：English   Publishing type：Rapid communication, short report, research note, etc. (scientific journal)   Publisher：AMER CHEMICAL SOC  

The magnetic property and decay kinetics of the nonphosphorescent triplet (T1) state of tropone in glassy matrices have been studied by employing the time-resolved EPR (TREPR) method with excimer and dye laser excitations. The T1 state was assigned to be nearly pure 3-pi-pi* in character from the small zero-field splitting (zfs) parameters (\D\ = 0.077 cm-1 and \E\ = 0.011 cm-1 in a toluene glassy matrix) and their small dependency on the matrix polarity. The directions of the principal axes of the zfs tensor were determined by magnetophotoselection experiments with two colors of lasers. It was found that the T1(pi-pi*) state of tropone has very short lifetime; the average rate constant from the zero-field spin sublevels is 2 x 10(5) s-1.

DOI： 10.1021/j100172a003

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Language：English   Publisher：AMER CHEMICAL SOC  

Photochemical hydrogen abstraction reactions and the lowest excited triplet states taking part in the initial process have been investigated for several pyridine derivatives by using the time-resolved EPR method. The emissive CIDEP spectrum obtained from the laser photolysis of 4-acetylpyridine (1) in 2-propanol was assigned to the corresponding ketyl radical, proving initial hydrogen abstraction by the carbonyl group. In the cases of 4-cyano-(2) and 4-methoxycarbonyl-(3) pyridines, and 4-pyridinecarboxamide (4), enhanced absorptive CIDEP spectra due to the corresponding 1-hydropyridinyl radicals were observed, suggesting the preferential population to the lowest sublevel in the intersystem crossing. The triplet EPR and phosphorescence spectra observed at 77 K indicate that T1 of 1 is mainly the carbonyl n-pi* state with a small contribution from the pi-pi* state. The T1 states of 2, 3, and 4 are considered to be of mixed character between the pyridine B3(1) (n-pi*) and A3(1)(pi-pi*) states, though the interaction is smaller than that of unsubstituted pyridine because of raising the pi-pi* state by electron-withdrawing groups. It is proposed that the T1 states of 2-4 have smaller deviation from the planar conformation than the T1 state of unsubstituted pyridine.

DOI： 10.1021/j100155a051

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Language：English   Publisher：AMER CHEMICAL SOC  

Photochemical hydrogen abstraction reactions and the lowest excited triplet states taking part in the initial process have been investigated for several pyridine derivatives by using the time-resolved EPR method. The emissive CIDEP spectrum obtained from the laser photolysis of 4-acetylpyridine (1) in 2-propanol was assigned to the corresponding ketyl radical, proving initial hydrogen abstraction by the carbonyl group. In the cases of 4-cyano-(2) and 4-methoxycarbonyl-(3) pyridines, and 4-pyridinecarboxamide (4), enhanced absorptive CIDEP spectra due to the corresponding 1-hydropyridinyl radicals were observed, suggesting the preferential population to the lowest sublevel in the intersystem crossing. The triplet EPR and phosphorescence spectra observed at 77 K indicate that T1 of 1 is mainly the carbonyl n-pi* state with a small contribution from the pi-pi* state. The T1 states of 2, 3, and 4 are considered to be of mixed character between the pyridine B3(1) (n-pi*) and A3(1)(pi-pi*) states, though the interaction is smaller than that of unsubstituted pyridine because of raising the pi-pi* state by electron-withdrawing groups. It is proposed that the T1 states of 2-4 have smaller deviation from the planar conformation than the T1 state of unsubstituted pyridine.

DOI： 10.1021/j100155a051

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Language：English   Publisher：CHEMICAL SOC JAPAN  

DOI： 10.1246/cl.1990.1491

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Language：English   Publisher：AMER CHEMICAL SOC  

DOI： 10.1021/j100357a015

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Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)   Publisher：CHEMICAL SOC JAPAN  

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DOI： 10.1246/nikkashi.1989.1463

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Language：English   Publisher：INST ORGANIC CHEM AND BIOCHEM  

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Language：English   Publisher：INST ORGANIC CHEM AND BIOCHEM  

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