Thiophene/selenophene-based S-shaped double helicenes: regioselective synthesis and structures.

2,5-Di(trimethylsilanyl)dithieno[2,3-:3',2'-]thiophene ((TMS)--), 2,5-di(trimethylsilanyl)diseleno[2,3-:3',2'-]thiophene ((TMS)--), and 2,5-di(trimethylsilanyl)diseleno[2,3-:3',2'-] selenophene ((TMS)--) were used as starting materials to synthesize three S-shaped double helicenes (i.e., -, -, and -) through monobromination, formylation, the Wittig reaction, and double oxidative photocyclization.