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Abstract 1,2-Bis(benzobthiophen-3-yl)ethene derivatives, which possess thermally irreversible and fatigue resistant photochromic properties, were synthesized, cis-1,2-Dicyano-1,2-bis(2-methylbenzobthiophen-3-yl)ethene 1a and 2,3-bis(2-methylbenzobthiophen-3-yl)maleic anhydride 2a underwent reversible photocyclization to produce red-colored closed-ring forms with λmax at 507 nm and 544 nm, respectively. The closed-ring forms were stable for more than 3 weeks at 80 °C. The coloration/decoloration (ring closure/opening)cycles were able to be repeated more than 104 times with keeping the adequate photochromic performance.
Uchida et al. (Tue,) studied this question.