Yoshio Sakaguchi

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.

Laser-photolysis study of the photochemical processes of carbonyl compounds in micelles under high magnetic fields

The magnetic field effects of the photochemical reactions of benzophenone derivatives and dibenzylketone were studied. The decay rate of the 4.4′-difluorobenzophenone ketyl radical in a sodium dodecylsulfate micelle continued to decrease from 2.9 × 106 s−1 at 0 T to 3.0 × 105 s −1 at 1.34 T.

Effects of high magnetic fields on the dynamic behavior of radical pairs generated in micellar solutions

Abstract Magnetic field effects on the dynamic behavior of radical pairs generated in micellar solutions of benzophenone, naphthoquinone, and 2′,3′,4′,5′,6′-pentafluoroacetophenone were studied under high magnetic fields (⩽10 T). For the reaction of pentafluoroacetophenone, the lifetime of a radical pair and the yield of the escaped ketyl radical were found to increase steeply with increasing field strength from 0 to 2 T, but to decrease gradually from 2 to 10 T. For the other reactions, such a phenomenon was not observed. These new magnetic field effects were explained in terms of the relaxation mechanism and the molecular dynamics in micellar solutions.

Internal magnetic field effect of lanthanoid ions on the photochemical reaction of naphthoquinone in a micelle

Abstract The effect of trivalent lanthanoid ions on the photochemical reaction of 1,4-naphthoquinone in a sodium dodecyl sulfate micelle is investigated in the

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.

Conformations of the triplet state of aromatic olefins. Observation of the transoid triplet states of 3,3-dimethyl-1-(2-naphthyl)-1-butene and 3,4-dihydrophenanthrene as a rigid planar triplet model

Abstract The observed triplet—triplet absorption of 3,3-dimethyl-1-(2-naphthyl)-1-butene is assigned to the planar transoid geometry ( 3 t*) from its spectral similarity to the 3,4-dihydrophenanthrene triplet, a rigid planar model, as well as from the measured rate constants for its quenching by azulene and oxygen. The results are in contrast the 1,2-diarylethylene triplets which favor the perpendicularly twisted geometry ( 3 p*).

Pulsed microwave irradiation effects on the dynamic behavior of a photochemically generated radical pair in a micellar solution

Abstract The radical pair dynamics in a photochemical hydrogen abstraction reaction of 2-methyl-1,4-naphthoquinone in a sodium dodecylsulfate micelle was modulated by a microwave pulse. After a short resonant 180° microwave pulse, the recombination of the radical pair was enhanced, its rate constant being determined to be (8.3±0.8)×106 s−1. Other kinetic parameters were determined by the scanning of the microwave pulse position as follows: the formation of the radical pair (3.3±0.3)×107 s−1, the relaxation rate from the triplet (T±1) levels to the singlet–triplet (T0) mixed one (3.3±0.3)×105 s−1 at 331 mT, and the radical escape rate (5.8±0.6)×105 s−1.

MAGNETIC FIELD EFFECTS ON THE PHOTOINDUCED ELECTRON TRANSFER OF 10-METHYLPHENOTHIAZINE WITH 4-(4-CYANOBENZOYLOXY) TEMPO IN FLUID SOLUTIONS

Abstract Magnetic field effects on both the quenching of the triplet excited state of 10-methylphenothiazine ( S =1) with 4-(4-cyanobenzoyloxy)TEMPO ( S =1/2) and the dynamic behavior of generated radical ion pairs ( S =1/2 and 3/2) were directly observed by a nanosecond laser photolysis technique. In 2-propanol, with increasing field from 0 T to 2 T, the quenching rate was decreased by (11.8±1.2)% and the yield of the escaped cation radical was increased by (90±8)%.

A laser flash photolysis study of the effects of ultrahigh magnetic fields up to 29.6T on dynamic behaviour of radical pairs in micellar solutions

Abstract The photoreduction of benzophenone in micellar SDS and Brij 35 solutions was investigated at room temperature under magnetic fields of 0–29.6T. In the SDS solution, the radical-pair lifetime increased with increasing field from 0T (0.4 μs) to 3.36T (1.6 μs), but the lifetime attained a constant value with increasing field from 3.36 and 29.6T. In the Brij 35 solution, the lifetime increased with increasing field from 0T (0.7 μs) to 3.36–6.30T (about 3 μs) and decreased with increasing field from 6.30 to 29.6T (2.1 μs), approaching a saturated value at 29.6T. These magnetic field dependences could be explained by the previous predictions derived from the relaxation mechanism.

Magnetic field effects on the photodissociation reaction of triphenylphosphine in non-viscous homogeneous solutions

Abstract Magnetic field effects on the photodissociation reaction of triphenylphosphine at 293 K were investigated in several non-viscous homogeneous solvents by means of a nanosecond laser photolysis technique under magnetic fields of 0–1.75 T. The generated neutral radical 3air of the diphenylphosphinyl and phenyl radicals showed clear magnetic field effects. The yield of the escaped diphenylphosphinyl radical at 1.5 T reduced to 74% ± 3% of that at 0 T in 2-propanol ( η = 2.379 at 293 K. Similar magnetic field effects were observed at 293 K even in more fluid solvents such as n -hexane (84% ± 5% at 1.5 T), cyclohexane (65% ± 2% at 1.5 T), and p -dioxane (64% ± 3% at 1.5 T).