Crystal Engineering of Angular-Shaped Heteroarenes Based on Cyclopenta[b]thiopyran for Controlling the Charge Carrier...

Cyclopenta[b]thiopyran, isomeric to benzo[b]thiophene while isoelectronic to azulene, is involved as a building block to construct soluble organic semiconductors for field-effect transistors. Two series of angular-shaped heteroarenes based on cyclopenta[b]thiopyran, that is, C-SS (n = 4, 6, 8, 10) with different linear alkyl groups and C-SS-Cl (m = 2, 3, 4) with chlorides substituted at different positions, have been straightforward synthesized. The obtained seven S-heteroarenes exhibit intriguing and similar photophysical and electrochemical properties, such as near-infrared absorption and high-energy levels of the highest occupied molecular orbitals. Nevertheless, the S-heteroarenes with identical π-conjugated skeletons demonstrate completely different molecular packing structures, which is proofed to be the key determinate factor for the charge carrier mobilities. Upon the engineering of the pendant alkyl lengths, the highest hole mobility in the C-SS series is achieved for C-SS (1.1 cm² V^-1 s^-1) with moderate alkyl length. The further incorporation of chlorides on C-SS results in the shortened intermolecular H···S contacts and the interplane distances. Most interestingly, when chlorine-containing chloroform and chlorobenzene are used as crystallization solvents, single crystals of C-SS-Cl with different packing structures are produced owing to the intermolecular interactions among the solute and solvent molecules. Upon further engineering of the chlorination position and the crystallization solvent, the maximum hole mobility in the ambient air improves to 2.7 cm² V^-1 s^-1 for C-SS-Cl crystallized from chlorobenzene, suggesting that the introduction of the accessible chlorides is a feasible pathway to engineering the crystal structures and controlling the charge transport characteristics.