Synthesis, X-ray crystallographic analysis, and theoretical structure analysis of tetrathienylethenes designed for photo- and electrochromism

As part of an effort to develop a new chromic system that responds to both photoexcitation and electron transfer, tetrakis(2-methylthien-3-yl)ethene (3a) and its tetrakismethylthio derivative (3b) were synthesized. The results of X-ray crystallographic and theoretical analyses of these substances suggest that (1) conformers of 3 with an antiparallel arrangement of two vicinal thienyl groups will undergo photocyclization, and (2) the most stable conformer of 3 having an anti-double parallel conformation will not. These predictions were preliminarily confirmed by the results of photochemical and cyclic voltammetry studies.