Photochromic dihetarylethenes 5. Synthesis, structure, and photochromic properties of 4,4 '-disubstituted 1,2-bis[2-ethyl-5-ethylthio(ethylsulfonyl)-3-thienyl]perfluorocyclopentenes

A series of new photochromic compounds were obtained for the first time fro m 1,2-bis(2-ethylthio-3-thienyl)perfluorocyclopente by substituting bromine atoms or carboxy, alkoxycarbonyl, and carbamoyl groups for hydrogen atoms in positions 4 and 4'. Introduction of these substituents causes a slight b athochromic shift (by 20-30 nm) of a long-wavelength absorption band for th e cyclic form and significantly increases the quantum yields of photocycliz ation Phi (A-->B) and ring opening Phi (B-->A). Depending on the nature of a substituent, Phi (A-->B) decreases in the order COOH > COOMe > CON HAr. T he quantum yields are markedly reduced when the ethylthio groups in positio ns 5 and 5' are replaced by ethylsulfonyl groups (a tenfold reduction in Ph i (A-->B) and a four- to fivefold reduction in Phi (B-->A)) The most consid erable bathochromic shift of a long-wavelength band and the highest quantum yields of forward and reverse photoreactions were observed for 1,2-bis(4-b romo-2-ethyl-5-ethylthio-3-thienyl)perfluorocyclopentene. 1,2-Bis(2-ethyl-5 -ethylthio-4-methoxycarbonyl-3-thienyl)perfluorocyclopentene was structural ly characterized by X-ray diffraction analysis.