Semiconductor Properties of π‐Extended 2‐(Thiopyran‐4‐ylidene)‐1,3‐benzodithiole (TP‐BT) Analogs

Abstract

Despite having an asymmetric structure, 2‐(thiopyran‐4‐ylidene)‐1,3‐benzodithiole (TP‐BT) is a good p‐type semiconductor containing isotropic three‐dimensional (3D) intermolecular interactions. Moreover, its π‐extended analogs can potentially work as organic electronic materials. Herein, a fused‐type π‐extended analog containing an extra benzene ring on the benzodithiole unit, i.e., 2‐(thiopyran‐4‐ylidene)‐1,3‐naphtho[2,3‐d]dithiole (TP‐NT), and three σ‐bonded‐type π‐extended analogs, i.e., phenyl‐, naphthyl‐, and anthryl‐substituted analogs (Ph‐TP‐BT, Nap‐TP‐BT, and Ant‐TP‐BT, respectively), were prepared and their molecular arrangements and organic field‐effect transistor (OFET) properties were investigated. TP‐NT formed a herringbone arrangement with 3D intermolecular interactions similar to that of the parent TP‐BT. Meanwhile, Ant‐TP‐BT formed a bilayer‐type layered herringbone arrangement. Since the highest occupied molecular orbital and the lowest unoccupied molecular orbital are located on the TP‐BT and anthracene units, respectively, a unique donor–acceptor separated network was formed. In OFETs prepared via a vapor deposition method using the σ‐bonded‐type analogs, slightly lower mobilities (0.1 to 8 × 10−3 cm2/Vs) than that of TP‐NT (0.1 cm2/Vs) were observed. Upon photo‐irradiation, the OFET of Ant‐TP‐BT exhibited a larger threshold voltage shift and an increase in the off current compared with TP‐NT. The σ‐bonded‐type analogs showed a larger photo‐response effect than TP‐NT derived from the donor–acceptor molecular structure.