Hiroki Kawata

Photodegradation of thin films of polygermanes

Abstract Upon ultraviolet irradiation of thin films of linear polygermanes in air, the germanium-germanium bond in thin films of polygermanes changed into digermoxane chains. The laser flash photolysis of the linear polygermane films showed the formation of polygermyl radicals generated by germanium-germanium bond homolysis as reactiev intermediated during photodegradation.

Photodimerization of 2,6-diphenylpyrylium salt in the solution

Abstract By the photoillumination of 2,6-diphenylpyrylium tetrafluoroborate (DPP) in tetrahydrofuran (THF), its dimer is confirmed to be formed through the pyranyl radical which is produced by one electron reduction of DPP.

A new type of photodimerization reaction for coumarin derivatives

Irradiation (λ >300 nm) of coumarin-3-carboxylic acid gives the decarboxylated 4,4′-dimer of chroman-2-one, the structure of which is quite different from that of [π2s+π2s] cycloaddition dimer as is observed in the past in the photoreaction of coumarin or some of its derivatives.

Photoreduction of flavone: identification of the photoproducts and reaction mechanism

Abstract The photoreduction of flavone was investigated in 2-propanol or in benzene containing N,N-dimethylaniline by a continuous light irradiation ( λ = 300 nm), a flash photolysis and CIDEP methods. The photoreaction proceeds via the triplet state of flavone and gives the dimers of flavanon in 2-propanol, the diastereoisomers, which are different from the pinacol-type dimer.

Photodimerization reaction of 10-methylacridone

Abstract The photoreaction of 10-methylacridone with N,N-dimethylaniline proceeds via the triplet state of the former and results in electron transfer followed

Photodecarboxylation of chromone-2-carboxylic acid in aerated and deaerated ethanol solution

Abstract The typical photodecarboxylation of chromone-2-carboxylic acid occurs in aerated and deaerated ethanol solutions to afford 4-hydroxycoumarin and 2-(1′-hydroxyethyl)-chromone, respectively. The former proceeds through an addition of the ground state oxygen molecule, while the latter through the recombination between the ketyl radical and the 1-hydroxyethyl radical followed by the release of CO2. Chemiluminescence technique was successfully applied to detect ketohydroperoxide intermediates assumed in the photoreaction of the aerated system.

Studies of photoinduced tautomerism of 2-hydroxyphenazine using flash photolysis

Abstract Flash photolysis of 2-hydroxyphenazine in aprotic and protic solvents gives the corresponding unstable ketonic form which reverts to the parent molecule in the dark. The activation energy and the frequency factor of the dark reaction were determined to be 6.1 ± 0.2 kcal mol −1 and 10 8 s −1 respectively. The rather small value of the frequency factor may be attributed to the weakness of the NH bond of the ketonic form. For 1-hydroxyphenazine, no transient is observed. It is suggested that a rapid deactivation of S 1 is induced by intramolecular hydrogen bond formation between the hydroxyl group and the nitrogen atom.

Flash photolysis of 2,2′,3,3′,5,5′,6,6′-octaphenyl-4,4′,-bi-4H-pyran: evidence for radical formation by photodissociation

Abstract The flash photolysis of the title compound 1 produced from 2,3,5,6-tetraphenylpyrylium salt by zinc metal reduction in deaerated tetrahydrofuran solution gives the corresponding unstable radical through σ-bonding cleavage between the 4- and 4′-carbons. The radicals recombine to give 1 with a rather high activation energy (5.13 kcal mol − ) because of the large steric hindrance of the phenyl groups at the 3- and 5-position carbons in the pyrylium ring.

Photoreaction of pyocyanine by continuous light illumination and flash photolysis

Abstract The results of a continuous light illumination and flash photolysis study of pyocyanine in deaerated 2-propanol are presented. The fully reduced compound, 5,10-dihydro-5-methylphenazine-1-ol (leucopyocyanine), is formed via a neutral radical intermediate. The photoproduct reverts to the cation radical by the addition of acid in vacuum. The mechanisms of the reduction and oxidation reactions are reported.

Mechanism of photodimerization reaction of 10-methylacridone in polar and non-polar solvents

The photodimerization reaction of 10-methylacridone (1) in the presence of N,N-dimethylaniline (2) was investigated both in deaerated benzene and acetonitrile solutions by a continuous light irradiation (λ > 350 nm) method and a flash photolysis. The photoreaction proceeds via the triplet state of 1(31*) and results in electron transfer followed by proton transfer from 2 to 1 to give the dimer. 9,9′-dihydroxy-10,10′-dimethyl-9,9′-biacridan (3).