Hisao Murai

CIDEP study of the formation of a cyclohexadienyl-type radical in the hydrogen abstraction reactions of triplet xanthone

Abstract From CIDEP measurements a new reaction of triplet xanthone, hydrogen abstraction by a benzene ring, was found to occur in the reactions with triethylgermane and sodium borohydride. An anomalous E/A phase pattern within each hyperfine line was also observed for the generated cyclohexadienyl-type radical in a micelle.

Time-resolved detection of spin-polarized ESR spectra of 9,10-anthraquinone triplet state in organic glass at 77K

Abstract Electron spin resonance spectra of the lowest excited triplet state of 9,10-anthraquinone are detected in a glass matrix at 77 K using a time-resolved technique. Computer simulation trials of the randomly oriented spin-polarized ESR spectra lead to the postulate of a wide distribution of the zero-field splitting parameters in the glass. The center values of the distributions and the population differences between the spin sublevels induced by the anisotropic intersystem crossing are estimated.

Time-resolved ESR study of the lowest excited triplet states of para-quinones in glassy matrices at 77 k

Abstract The lowest excited nπ* triplet of 9.10-anthraquinone, 1.4-naphthoquinone and 1,4-benzoquinone were studied in glassy matrices at 77 K using a time-resolved ESR method. The D value of the triplet state of 9,10-anthraquinone varied from −0.351 cm −1 in a polar solvent to −0.318 cm −1 in a non-polar solvent. Both 1,4-naphthoquinone and 1,4-benzoquinone in polar solvents showed triplet state spectra with a D value of −0.330 cm −1 . A computer simulation revealed the existence of widely distributed zero-field splitting parameters in the glassy condition. These data are compared with an analysis of CIDEP results of para-quinones.

Intermolecular energy transfer of the spin-polarized triplet state in a γ-cyclodextrin cavity

Abstract The triplet-triplet energy-transfer process from xanthone to naphthalene was studied in a γ-cyclodextrin system at 77 K using a time-resolved ESR method. The efficient inclusion of these two molecules and the formation of a fixed configuration between them in a γ-cyclodextrin cavity were found with the aid of spin polarization transfer.

Intermolecular energy transfer of the spin polarized triplet state in frozen SDS micelles

Abstract Triplet—triplet energy transfer from benzophenone to naphthalene and biphenyl was studied in frozen SDS micelles at 77 K using a time-resolved ESR method. The efficient solubilization of both energy donor and acceptor molecules in the micelles and the formation of a unique configuration between them in the frozen condition were directly observed.

Time-resolved ESR study of the triplet state of xanthone and the triplet-triplet energy transfer in cyclodextrins

Abstract The triplet state of xanthone embedded in a cyclodextrin cavity is studied using time-resolved ESR. α-, β- and γ-cyclodextrins provide different characteristic spectra of the xanthone triplet state, and these spectra clearly show the different inclusion conditions for xanthone in cyclodextrins. In γ-cyclodextrins, more than two molecules can be trapped in its cavity. The specific spin polarization induced through triplet-triplet energy transfer between aromatic molecules proves some fixed orientation of the energy donor and acceptor in γ-cyclodextrin. It is also shown that two xanthone molecules can be included in γ-cyclodextrin and the spin polarized triplet exciton is interchanged between them.

CIDEP study of two photochemical processes of triplet-state benzophenone and N,N-diethylaniline system in polar and non-polar media

Abstract The photochemical reactions between nπ * triplet benzophenone and N,N-diethylaniline have been studied by the CIDEP method in both polar and non-polar media. The total emission pattern of the spectrum detected after pulsed excitation reveals a predominant contribution of the triplet mechanism in both media. The observed CIDEP clearly indicates the existence of two different processes depending on the polarity of the solvents.

Singlet precursor cidep observed in the photolysis of tetraphenylhydrazine

Abstract The formation and dynamics of the diphenylamino radical from photolyzed tetraphenylhydrazine have been studied using a CIDEP technique. The absorption/emission polarization pattern observed in this study is explained by the singlet precursor radical pair mechanism. A weak polarization by the free pair precursor appears along with the spectrum of the thermal distribution at long time.

Photosensitized triplet state of stilbene detected by a time-resolved ESR method

Abstract The spin-polarized excited triplet state of stilbene formed by the photosensitization in a micellar aggregate, which was employed as an efficient reaction field, has been detected by a time-resolved ESR technique. Both trans- and cis-stilbene provided triplet states having nearly identical zfs constants.

Spin-polarized radical pairs transiently produced by the photochemical reaction of benzophenone with aromatic amines

Abstract Spin-polarized triplet radical pairs produced by the photochemical reaction of triplet benzophenone with aromatic amines were detected in glassy matrices at 77 K using a time-resolved ESR method. By analysis of the spectra, it is concluded that the population of the Z spin sublevel of the radical pair whose principal axis is nearly parallel to the direction of the carbonyl group of benzophenone is predominant and its spin polarization is transferred from the initial polarization of the triplet state of benzophenone.