Synthesis, crystal structures and semiconductor properties of 2-(thiopyran-4-ylidene)-1,3-benzodithioles with an aryl substituent

Abstract

Three 2-(thiopyran-4-ylidene)-1,3-benzodithiole (TP-BT) derivatives containing a phenyl (1), 2-pyridyl (2) or 4-pyridyl (3) group on the benzene moiety were synthesized to investigate the relationship between their molecular structure and semiconductor properties. Analysis of molecular orbital calculations revealed that the highest occupied molecular orbitals of 1–3 were distributed on the TP-BT moieties, and the lowest unoccupied molecular orbitals were located on the introduced aryl substituents, leading to donor–acceptor (D–A) type molecular structures. X-ray analysis of the two pyridyl-substituted compounds (2 and 3) revealed that 2-pyridyl-containing compound 2 formed a crystal structure with D–A segregated-type stacking through the formation of a hydrogen bond between the pyridyl nitrogen atom and the thiopyranyl hydrogen atom. 4-Pyridyl-containing compound 3 formed a D–A mixed-type layer structure in which molecules were aligned in an antiparallel fashion. The XRD analysis of 1–3 thin films revealed that d-spacings were close to their molecular lengths for all three compounds and the molecules formed edge-on arrangements on the substrates. Employing 1–3 as active layers in organic field-effect transistor (OFET) devices resulted in compound 1 exhibiting the highest hole mobility among these derivatives. The OFET device formed from 2 demonstrated less effective hole-transport properties; however, the device possessed a more stable small off current. The device formed from 3 was only active under photo-irradiation conditions, resulting in a unique photo-active OFET.