Electronic Structures and Mobilities of 2,2'- diphenyl-5,5'-bithiazole Derivatives

Density functional theory calculations were performed on 2,2'-diphenyl-5,5'-bithiazole (DPBT) and its derivatives. The dimer structures of the title compounds were optimized by a density functional theory method with dispersion energy being considered at the wB97XD/LanL2DZ level. Reorganization energies between the switch of neutral molecules and anion radicals, and the electron-transfer coupling matrix were obtained. By using the Marcus theory and the Einstein relation, the electron hopping rates and mobilities were predicted. The electron mobility of difluorinated 2,2'-diphenyl-5,5'-bithiazole (2A) was predicted to be 1.179 cm2 V–1 s–1, which is the largest value among the title compounds. The large electron mobility of 2A is mainly owing to its large transfer coupling matrix since its LUMO consists of some overlaps between two submolecular orbitals. Our results indicate that a moderate fluorination of DPBT, instead of as many as possible substituents of fluorines, considerably facilitates the electronic mobility of n-type organic semiconductors.