Photochromism of Hemithioindigo Derivatives. I. Preparation and Photochromic Properties in Organic Solvents

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Thirteen hemithioindigo (HT) derivatives bearing alkyl chains are newly synthesized and their photochromism and emission properties are investigated. The Z/E photoisomerisms of these compounds in organic solvents are essentially in agreement with data reported by Mostoslavskii and Izmail’skii (J. Gen. Chem. USSR, Engl Transl.), 31, 21 (1961), and subsequent papers). At 77 K both the E and Z isomers of HT chromophore emit fluoresscences of comparable intensities, whereas at room temperature very weak fluorescence is observed only from the Z isomer. Examination of repeatable numbers of Z/E photoisomerization reveals that the HT chromophore possesses remarkable inherent photofatigue resistance.