Photochromism of dithiazolylethenes having pyridyl and N‐methylpyridinium groups

Abstract

AbstractDithiazolylethenes 1a and 2a having 4‐ or 3‐pyridyl groups and 3a having N‐methylpyridinium groups at thiazole rings were prepared and their photochromic performance was examined. Upon irradiation with 313 nm light the colorless acetonitrile solutions of 1a and 2a turned violet, which show the absorption maxima at 538 and 530 nm, respectively. The violet color is due to the closed‐ring isomers 1b and 2b. The violet color disappeared upon irradiation with visible light (λ > 480 nm). When the pyridine rings were converted to N‐methylpyridinium ions, the colorless acetonitrile solution of 3a turned blue (λmax = 596 nm) upon irradiation with 365 nm light. The absorption maximum of the closed‐ring isomer 3b showed a bathochromic shift as much as 58 nm relative to the maximum of 1b. In methanol 3a changed to green (λmax = 750 nm) upon irradiation with 365 nm light. It was suggested J‐aggregates of 3b are formed in methanol. Copyright © 2007 John Wiley & Sons, Ltd.