LIGHT-INDUCED J-AGGREGATION IN MIXED LANGMUIR-BLODGETT-FILMS OF SELENIUM-CONTAINING CYANINE AND AZOBENZENE

In the mixed Langmuir-Blodgett (LB) films of a selenium-containing cya nine dye and an azobenzene derivative (molecular ratio = 3:1), the azo benzene photoisomerized reversibly by the alternate illumination with UV and visible light. After three cycles of photoisomerization, the J- band of the cyanine dye started to develop and reached a saturated sta te after 12 h, when the samples were stored in the dark. A drastic cha nge in the morphology of the mixed LB films occurred with the developm ent of the J-band. When the J-band was fully developed, a number of co nes protruded from the film surface which should be due to the formati on of J-aggregate of the cyanine dye. The size of the largest cones wa s ca. 250 nm in height and ca. 2000 nm in diameter at the base. The li ght-induced J-aggregation in the present case is similar in nature to the previously reported case (M. Matsumoto et al., J. Phys. Chem. B 10 1 (1997) 702). However, the number of cones is smaller, the size large r, and the time necessary for the full development of the cones longer in the present case compared with the previous case. (C) 1998 Elsevie r Science S.A. All rights reserved.