Diseleno[2,3‑<i>b</i>:3′,2′‑<i>d</i>]selenophene and Diseleno[2,3‑<i>b</i>:3′,2′‑<i>d</i>] thiophene: Building Blocks for the Construction of [7]Helicenes

New building blocks, 2,5-di­(trimethylsilanyl)­diseleno­[2,3-<i>b</i>:3′,2′-<i>d</i>]­selenophene ((TMS)₂-<b>DSS</b>) and 2,5-di­(trimethylsilanyl)­diseleno­[2,3-<i>b</i>:3′,2′-<i>d</i>]­thiophene ((TMS)₂-<b>DST</b>), for helicenes were obtained from selenophene with total yields of 54 and 61%. From (TMS)₂-<b>DSS</b> and (TMS)₂-<b>DST</b>, selenophene-based hetero[7]­helicenes, 5,5′-di­(trimethylsilanyl)­benzo­[1,2-<i>b</i>:3,4-<i>b</i>′]­bis­(diseleno­[2,3-<i>b</i>:3′,2′-<i>d</i>]­thiophene) (<i>rac</i>-<b>1</b>), and 5,5′-di­(trimethylsilanyl)­benzo­[1,2-<i>b</i>:3,4-<i>b</i>′]­bis­(diseleno­[2,3-<i>b</i>:3′,2′-<i>d</i>]­selenophene) (<i>rac</i>-<b>2</b>) 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 <i>rac-</i><b>1</b> and <i>rac-</i><b>2</b>. In addition, the absorption behaviors of <i>rac-</i><b>1</b> and <i>rac-</i><b>2</b> were investigated