Yasumasa J. I'Haya

CIDEP study of the photochemical reactions of carbonyl compounds showing the external magnetic field effect in a micelle

Abstract The dynamics of naphtosemiquinone and SDS alkyl radicals were studied by CIDEP in a micellar solution. The total emission pattern of the spectrum detected at an early stage after pulsed excitation revealed a predominant contribution of the triplet mechanism. The radical pair mechanism became observable at a later stage. The effect of an external magnetic field discussed.

Evaluation of molecular spin-orbit integrals by a gaussian expansion method

A method is presented for the evaluation of molecular multi-centre spin-orbit integrals of Coulomb, hybrid and exchange types using cartesian gaussian functions. It is shown that if gaussian bases are employed the spin-same-orbit integrals reduce to one-electron field integrals and the spin-other-orbit integrals to two-electron field integrals. The final formulae for these integrals are found to be convenient for computer programming. Some relationships among the nuclear attraction, the field and the field-gradient integrals as well as among the electronic repulsion, the two-electron field, and the zero-field splitting integrals are discussed in connection with the spin-orbit integrals. Some calculations are carried out for the radicals CH2 and NH.

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.

Formation of α-keto alkyl radical in the photoreduction of chromone as studied by the laser photolysis—ESR technique

Abstract In the photochemical hydrogen abstraction reactions of chromone in 2-propanol at room temperature, beside its ketyl radical, the α-keto alkyl radical from chromone was observed, with the aid of the time-resolved electron spin resonance technique. When tri-n-butylin hydride was used as a hydrogen donor, the α-keto alkyl radical was produced predominantly from the lowest ππ* triplet state. The formation of such a non-ketyl radical in the hydrogen abstraction reaction with both of the hydrogen donors indicates the popularity of the hydrogen abstraction reactions from the ππ* triplet state of aromatic carbonyl compounds.

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.

Predictions of molecular geometries and electronic spectra of complex unsaturated molecules from MC-LCAO-MO method with particular reference to triplet-triplet transitions of naphthalene

An MC-LCAO-MO approach which has been proposed for open-shell systems of unsaturated hydrocarbons having degenerate MOs is applied to naphthalene, calculating its molecular geometry and electronic spectrum. The results are compared with those obtained by the usual semi-empirical SCF-CI method and with experiment. As for benzene, anthracene, phenanthrene and triphenylene, the bond lengths and the π-electron energies in their ground states are calculated in the same manner. Most of the calculated bond lengths are in fairly good agreement with experiment. The total π-electron energies of the ground states obtained by the MC-LCAO-MO and SCF-CI methods agree within about 0.01 eV when CI is included and within about 0.1 eV when CI is not invoked. It is found that the electronic spectrum of naphthalene obtained by the present method is in good agreement with that derived from the SCF-CI method and also explains most part of experiments. A detailed discussion is given on the calculated triplet-triplet absorption spectrum and its intensity distribution of naphthalene.

Evaluation of molecular integrals by gaussian expansion method with particular reference to zero-field splitting integrals

Abstract A new method is presented for deriving necessary molecular integrals of spin—orbit coupling and zero-field splitting integrals in benzene show that the contribution of the delta function integrals is large.

Time-resolved electron spin resonance study of hydrogen abstraction reaction of aromatic carbonyl compounds in their ππ* triplet states

Abstract With aid of the time-resolved electron spin resonance technique, the photochemical hydrogen abstraction reactions were investigated for the aromatic carbonyl compounds having ππ* characters in their lowest triplet states. When the hydrogen donors having negatively charged hydrogen atoms, such as NaBH 4 , Et 3 GeH (EtC 2 H 5 ) and n -Bu 3 SnH (BuC 4 H 9 ), are used as the hydrogen donors, these ketones reacted readily with them to form non-ketyl radicals, such as cyclohexadienyl-, benzyl- and α-keto alkyl-type radicals instead of their ketyl radicals. The instrinsic reactivity of the ππ* triplet states is inhibited by the positively charged hydrogen atoms in the usual hydrogen donors since they have a strong affinity for the reaction around the negatively charged carbonyl oxygen.

Optimization with a direct search for orbital localization

Abstract Two direct-search approaches to obtain the SCF solution for a true maximum of the self-repulsion energy with energy-localized orbitals are proposed: an approach based on the level-shifted second-order method and another approach based on scaling of the orbital transformation vector to obtain an approximate solution for a true maximum. The latter is more advantageous to obtain convergence for large systems. Both methods involve calculation of the exact self-repulsion energy hypersurface in the controlling parameter space via a set of unitary transformations and selection of the unitary transformation which increases the self-repulsion energy. These approaches are found to converge efficiently even when started from a point far from convergence.

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.