One-pot photochemical synthesis of novel thienobis[1]benzothiophene with an angularly-fused structure that promotes unique intermolecular S⋯S contacts in the crystalline state

4,8-Di(thien-3-yl)thieno[2,3-g:5,4-g′]bis[1]benzothiophene (8a), a member of a new class of angularly-fused thienobis[1]benzothiophenes (TBBTs), was synthesized by using a one-pot photocyclization–dehydrogenation reaction of 2,5-bis[2,2-di(thien-3-yl)ethenyl]thiophene (7a). The results of absorption and emission spectroscopy, and cyclic voltammetry studies suggest that the effective conjugation length of 8a is shorter than that of 7a. X-ray crystallographic analysis revealed that the core TBBT framework of 8a is slightly twisted. In the crystalline state, molecules of 8a are arranged in stacked columns that interact with the adjacent stacked columns via S⋯S contacts. Moreover, a 1:1 charge-transfer complex between 8a and 7,7,8,8-tetracyanoquinodimethane (TCNQ) forms crystals that have an alternating stacked columnar structure with both 8a and TCNQ being aligned in individual ribbon-like motifs. The crystal properties of these substances suggest that the angularly-fused TBBT framework might be a useful platform for the construction of electrically interesting materials.

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