Synthesis and Structures of Unsymmetrical Bull’s Horn-Shaped Heptathienoacenes with Isomeric Location of Sulfur Atoms

Controlling and balancing the isomeric location of sulfur atoms in thienoacenes are important strategies to tune the functions of intramolecular π-electronic conjugation and intermolecular interactions. In this work, three kinds of unsymmetrical bull's horn-shaped heptathienoacenes (1–3) and one kind of symmetrical bull's horn-shaped heptathienoacene (4) with different isomeric locations of sulfur atoms in the two terminal thiophene rings have been successfully designed and synthesized using dithieno[3,2-b:3′,4′-d]thiophene (st-DTT), dithieno[2,3-b:2′,3′-d]thiophene (bt-DTT), and dithieno[3,2-b:2′,3′-d]thiophene (tt-DTT) as building blocks through the Suzuki cross-coupling and intramolecular cyclization reactions. The results of single-crystal analysis, electrostatic potential measurement, UV-vis absorption spectroscopy, fluorescence spectroscopy and cyclic voltammetry show remarkable structure–property relationships. On the one hand, the isomeric location of sulfur atoms in the two terminal thiophene rings in 1–4 leads to different intermolecular interactions, resulting in different crystal packing patterns. On the other hand, the isomeric location of sulfur atoms plays a key role in intramolecular π-electronic conjugation and exhibits rich absorption behaviors.