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

2,5-Di(trimethylsilanyl)dithieno[2,3- b :3',2'- d ]thiophene ((TMS) 2 - bb - DTT ), 2,5-di(trimethylsilanyl)diseleno[2,3- b :3',2'- d ]thiophene ((TMS) 2 - bb - DST ), and 2,5-di(trimethylsilanyl)diseleno[2,3- b :3',2'- d ] selenophene ((TMS) 2 - bb - DSS ) were used as starting materials to synthesize three S-shaped double helicenes (i.e., DH - 1 , DH - 2 , and DH - 3 ) through monobromination, formylation, the Wittig reaction, and double oxidative photocyclization. The photocyclization was a highly regioselective process. The molecular structures of DH - 1 and DH - 2 were confirmed by X-ray single-crystal analysis. Multiple intermolecular interactions, such as C-S, C-Se, S-S, S-Se, and Se-Se, were observed in the crystal packing structures of these compounds. Spectroscopic results and our previous work showed that the combination of molecular structure change and heteroatom replacement from S to Se could precisely modulate molecular energy levels.