Chiral Helicenoid Diarylethene with Large Change in Specific Optical Rotation by Photochromism^1,2

A diarylethene possessing one [4]thiaheterohelicene and one benzothiophene, the latter with a chiral methoxymethoxyethyl group on its C-3 position, was proved to work as a switch of specific optical rotation at a wavelength at which both colored and colorless forms have no absorption in solution. The difference of the specific optical rotation was 1300° between the open form and the photostationary state. The specific optical rotation of one of the isolated optically active major colored forms was −4680°. The conversion to the colored form was 64%, and the diastereomeric excess of photocyclization was 47%.