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

DOI： 10.1021/acs.jpclett.3c00341

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

DOI： 10.1063/5.0143683

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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)  

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

DOI： 10.1021/acs.langmuir.2c00290

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

DOI： 10.1002/cptc.202200100

Scopus

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

DOI： 10.1246/bcsj.20220002

Scopus

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

DOI： 10.1021/acs.jpcc.1c07807

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

DOI： 10.1021/acs.jpcc.1c06879

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

DOI： 10.1002/cplu.202100429

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

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

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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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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DOI： 10.1063/1.5127940

Web of Science

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

DOI： 10.1016/j.orgel.2019.105383

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

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

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

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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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)  

DOI： 10.1016/j.tet.2015.06.071

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

DOI： 10.1021/acs.jpca.5b02253

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

DOI： 10.1021/jz502495u

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

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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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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DOI： 10.1021/jp802810s

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

Abstract

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

DOI： 10.1002/chin.200830061

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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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Language：Japanese   Publishing type：Research paper (international conference proceedings)  

Scopus

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Language：Japanese   Publishing type：Research paper (international conference proceedings)  

Scopus

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

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

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

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

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

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

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

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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Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

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

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

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)  

DOI： 10.1246/cl.1990.1491

Web of Science

CiNii Article

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Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1021/j100357a015

Web of Science

CiNii Article

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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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