Y.J. I'Haya

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 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.

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.

Linear response polarizability theory of the ORD and the CD spectra of helical biopolymers

Abstract The linear response theory of configurationally induced optical rotation for helical biopolymers is formulated in terms of the molecular polarizability. Simple numerical computation of the ORD and the CD curves is carried out for the single-stranded polyadenylic acid having the configuration of DNA.

Comments on the symmetry-adapted perturbation treatments of molecular interaction

Abstract Symmetry-adapted perturbation theories published so far are criticised. Extra conditions imposed in most of these formalisms are found to be not always physically adequate. We conclude that the formalism proposed by Hirschfelder and Silbey is the most appropriate.

CD and UV absorption bandshapes of DNA—acridine orange complexes: Influence of the interactions of purine—pyrimidine base pairs with dyes in intercalated model complexes

Abstract Induced CD and UV absorption spectral bandshapes of DNA—acridine orange (AO) complexes have been calculated for a model in which DNA intercalates one AO dye between every other base pair ( P/D =4), using the linear response polarizability theory of copolymer systems. The spectra show a strong dependence on the intercalated positions and the orientational angles of the AO dyes in the DNA pocket. The base pair sequence effect in the bandshapes which reflects the interaction of AOs with the DNA bases can clearly be observed, particularly in the ultraviolet region. It is necessary to take into account the interactions of DNA bases with AOs in electronic excited states in order to calculate reliable induced CD and UV absorption spectral bandshapes.

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.

Solvent dependence of excited molecule-free radical interactions studied by means of time-resolved electron spin resonance

Abstract Electron spin polarization transfer phenomena have been studied by time-resolved electron spin resonance spectroscopy with pyrazine as a donor and nitroxyl radicals as acceptors. We found that mechanisms are different depending on solvents used. Importance of doublet to doubler spin polarization transfer is demonstrated in 2-propanol solutions.

A polarizability theory for Z-DNA: UV absorption and CD bandshape calculations for the B-to-Z transition of poly(dG-dC)•poly(dG-dC)

Abstract A polarizability theory is presented for copolymers perturbed by solvent molecules. The hypochromic red-shift of the UV absorption spectrum and the inversion of the CD profile for the B-to-Z transition of poly(dG-dC)·poly(dG-dC) are calculated by the most simplified scheme of this theory. The bandshapes qualitatively characterize the experimental results.