Effect of Nitrogen Substitution in Nonlinear Thienoacene: Theoretical Study on Charge Transport Properties in Organic Field-Effect Transistors

Owing to their high carrier mobility, thienoacenes have been widely used in organic field-effect transistors. To design a highly efficient organic semiconductor, a fundamental understanding of the charge transport properties originating from intramolecular and intermolecular electronic interactions is of great importance. In this study, the charge transport properties of a nonlinear thienoacene and its nitrogen-substituted derivative, naphtho[2,1-b:3,4-b']bis[1]benzothiophene (DTNN) and quinoxalo[6,5-b:7,8-b']bis[1]benzothiophene (DTNQ), were investigated by theoretical modeling and density functional theory calculations. The charge transport rate based on the Marcus theory, and the theoretical mobilities of DTNN and DTNQ were evaluated via reorganization energy and transfer integral calculations. Nitrogen substitution caused a slight increase in the hole reorganization energy, but the hole transfer integral was significantly increased. As a result, DTNQ showed higher hole mobility than DTNN. Thus, nitrogen substitution in nonlinear thienoacene is an efficient strategy for realizing high-mobility OFETs.