Diseleno[2,3-b:3',2'-d]selenophene and Diseleno[2,3-b:3',2'-d] thiophene: Building Blocks for the Construction of [7]Helicenes.

New building blocks, 2,5-di(trimethylsilanyl)diseleno[2,3-b:3',2'-d]selenophene ((TMS)2-DSS) and 2,5-di(trimethylsilanyl)diseleno[2,3-b:3',2'-d]thiophene ((TMS)2-DST), for helicenes were obtained from selenophene with total yields of 54 and 61%. From (TMS)2-DSS and (TMS)2-DST, selenophene-based hetero[7]helicenes, 5,5'-di(trimethylsilanyl)benzo[1,2-b:3,4-b']bis(diseleno[2,3-b:3',2'-d]thiophene) (rac-1), and 5,5'-di(trimethylsilanyl)benzo[1,2-b:3,4-b']bis(diseleno[2,3-b:3',2'-d]selenophene) (rac-2) were prepared. The overall yields from selenophene were approximately 6.5 and 6.1%, respectively. Intermolecular interactions such as C-Se, C-S, and Se-Se were observed in the crystal packings of rac-1 and rac-2. In addition, the absorption behaviors of rac-1 and rac-2 were investigated.