Masao TAKAYANAGI (Tokyo Univ. Agric. and Tech. and IMS), Munetaka NAKATA (Tokyo Univ. Agric. and Tech.), Yukihiro OZAKI (Kwansei-Gakuin Univ.), Keiji IRIYAMA (The Jikei Univ. School of Medicine) and Mitsuo TASUMI (Univ. Tokyo)
[J. Mol. Struct. 405, 239 (1997)]
The photoisomerization of the merocyanine dyes, 5-[2-(3-ethyl-2-benzothiazolylidene)-1-methyl-ethylidene]-3-ethyl-2-thioxo-4-thiazolidinone [Et(Me)MD] and 5-[2-(3-ethyl-2-benzothiazolylidene)ethylidene]-3-ethyl-2-thioxo-4-thiazolidinone [EtMD], in solution was studied by visible absorption, resonance Raman and IR spectroscopies. It was found that the most stable conformers for Et(Me)MD and EtMD of the four possible isomers A-D were different. For Et(Me)MD, isomer A, which was stable in cyclohexane and carbon tetrachloride, was photoisomerized to isomer C by 514.5 nm laser irradiation. Isomer C returned to isomer A slowly in the dark or rapidly on 488.0 nm laser irradiation. In contrast, Isomer C for EtMD, which was stable in the solvents, was photoisomerized to Isomer A by 488.0 nm or 457.9 nm laser irradiation. Isomer A returned to Isomer C slowly in the dark or rapidly on 514.5 nm laser irradiation in cyclohexane. Possible photoisomerization mechanisms are discussed based on the rotational motions around the two C=C double bonds of the central conjugated system.