Structurally versatile novel photochromic bisarylindenone and its acetal: achievement of large cyclization quantum yield.

Bisarylindenones and an acetal derivative, a novel thermally irreversible photochromic family based on 6pi-electrocyclization with three easily modifiable functional groups, have been synthesized. 2,3-Bis(5-methyl-2-phenyl-4-thiazolyl)indenone showed photochromic back-and-forth reactions with two different visible lights. Its ethylene acetal recorded 0.81 as the photocyclization quantum yield in hexane, which is the largest value known to date for 6pi-electrocyclization in solution.