Setsuko Irie

Photoinduced pitch changes in chiral nematic liquid crystals formed by doping with chiral diarylethene

Chiral binaphthyl derivatives having two photochromic diarylethene units were synthesized in an attempt to use them as dopants for photoresponsive liquid crystals. These compounds showed thermally irreversible photochromic reactions. The circular dichroism (CD) spectra and the optical rotation values of the derivatives reversibly changed in methanol upon alternate irradiation with ultraviolet and visible light. Large photostimulated pitch changes of chiral nematic K-15 liquid crystals were observed on addition of the derivatives as dopants. The relation between the optical rotation and the twisting power force was discussed.

Phase Transition of a Liquid Crystal Induced by Chiral Photochromic Dopants

Abstract A chiral cyclohexane having two photochromic diarylethene unit was synthesized in an attempt to use it as a dopant for a photoresponsive liquid crystal. A stable photoswitching between nematic and cholesteric phases could be induced by the addition of a small amount of the chiral cyclohexane to a nematic liquid crystal 4-cyano-4′-penthylbiphenyl (K-15).

Photoswitching of Helical Twisting Power by Chiral Diarylethene Dopants

Abstract Photochromic chiral compounds having two diarylethene units were synthesized in an attempt to use them as dopants for photoresponsive liquid crystals. Stable photoswitching of the photochromic dopants induced large pitch changes of chiral nematic liquid crystals composed of K-15 and a small amount of the chiral dopants.

Electronic spectra of radical ions of cyclic polysilanes

The absorption spectra of the radical ions of cyclic polysilanes, (Me2Si)n, where n = 5, 6, and 7, formed by γ-irradiation have been recorded for rigid matrices at 77 K. The absorption maxima of radical anions of the cyclic polysilanes showed a red shift from 670 to 900 nm with increasing ring size. shows a broad single band at 720 nm, whereas shows two bands in the wavelength region from 500 to 1000 nm. A single peak is observed for at 900 nm. Ring-size reduction of the cyclic polysilanes with production of dimethylsilylene was not observed for the radical ions below 173 K, in sharp contrast to the behavior shown by the photoexcited states.

Electronic absorption spectra of radical ions of alkyl silicon network polymers

Abstract Absorption spectra of radical ions of silicon network polymers formed by γ -irradiation have been measured in rigid matrices at 77 K. Both the radical anion and cation showed very broad absorption bands in visible and near-infrared wavelength regions. The radical anion spectrum was sensitive to photoillumination and changed the band shape by selective photobleaching. Thermal annealing of the radical cation caused a blue shift of the absorption spectrum. The broad band shape and the selective band bleaching indicated the coexistence of various cyclic structures in the network polysilane radical ion spectra.

Radiation Sensitivity of Photochromic Diarylethenes

Abstract The radiation sensitivity of photochromic dithienylethenes was studied with the aim of developing a new reusable color film dosimeter. Upon γ-irradiation, polystyrene films containing 1,2-bis(2,5-dimethyl-3-thienyl)perfluorocyclopentene 1 and 1,2-bis(2-methyl-5-phenyl-3-thienyl)perfluorocyclopentene 2 turned red and blue, respectively. The red and blue colors disappeared by visible-light irradiation and the films could be reused. In both films the absorption intensities of the colors linearly increased with the absorbed dose. From the color change it was possible to estimate the radiation dose.

γ-Ray- and UV-induced generation of methyl(phenyl)silylene and silene species from heptamethyl-2-phenyltrisilane

A benzene solution of heptamethyl-2-phenyltrisilane (1) has been irradiated with γ-rays in the presence of methanol. Hexamethyldisilane, methoxymethyl(phenyl)silane (2) and a 1-methoxytetramethyldisilanyl- and trimethylsilyl-substituted cyclohexadiene (3) were produced. The formation of 2 and 3 can be interpreted in terms of reactions of methanol with methyl(phenyl)silylene and a silicon–carbon double-bonded intermediate (silene), respectively. These intermediates are generated as follows. Benzene is first excited by γ-rays and by collisions the energy transfers to 1. Excited 1 decomposes to give methyl(phenyl)silylene or undergoes rearrangement to a silene intermediate as when 1 is excited by UV light. A kinetic study revealed that the energy transfer in the γ-irradiated system is the same as that in a UV-irradiated system.

The Radiation-Induced Coloration of Dithienylethene Amorphous Films

ABSTRACT The radiation-induced coloration of bulk amorphous films of five photochromic diarylethenes was studied with the aim of developing reusable, sensitive color dosimeters. Although amorphous films of bisbenzothienylentene derivatives 3 , 4 and 5 exhibited only weak coloration upon γ-irradiation, intense coloration was observed for the film containing 1,2-bis(2,4-dimethyl-3-thienyl)perfluorocyclopentene 1 having diphenylphenyl substituents. The color was stable in the dark, but disappeared upon irradiation with visible light. The sensitivity remained at 80% of the initial value even after 10 cycles.

Ultrasonic degradation of alkyl-substituted polysilanes

Abstract The degradation of poly(methyl-n-propylsilane), poly(di-n-butylsilane) and poly(di-n-hexylsilane) by ultrasonic irradiation has been studied in various solvents. The changes in the optical absorption spectra of the polymer solutions and the molecular weight distributions have been followed as a function of time. Although efficient degradation of poly(methyl-n-propylsilane) was observed in CCl 4 , the polymer scarcely decomposed in toluene and cyclohexane. The decrease in the molecular weight was initially rapid but slowed with time and reached a limiting value. The rate of degradation and the limiting chain length were dependent on the size of the substituents. Polysilanes with bulky substituents such as poly(di-n-hexylsilane) and poly(di-n-butylsilane) degradated slower than poly(methyl-n-propylsilane) and the degradation yielded higher limiting molecular weights.