Novel naphthalene-diimide-based small molecule with a bithiophene linker for use in organic field-effect transistors

Abstract

We report on the synthesis and characterization of a novel naphthalene diimide (NDI)-based small molecule with a bithiophene linker unit, NDI-BT-NDI-EH, for application as a solution-processable n-channel active material in organic field-effect transistors (OFETs). NDI-BT-NDI-EH was synthesized via the Stille coupling reaction and the bithiophene linker unit was introduced as a rotatable linker between two NDI cores to improve the solubility of NDI-BT-NDI-EH while maintaining its high field-effect mobility. We found that the crystallinity and molecular ordering of NDI-BT-NDI-EH thin films could be improved by thermal annealing; a moderate annealing temperature of 120 degrees C appeared to be optimal for promoting self-organization among the NDI-BT-NDI-EH molecules. The NDI-BT-NDI-EH molecules in thermally annealed thin films mainly adopted an edge-on orientation with improved pi-pi stacking on the surface of octyltrichlorosilane-treated SiO2 substrates, which is favorable for lateral charge transport. As a result, the optimally annealed NDI-BT-NDI-EH OFET exhibited evident n-type OFET characteristics with high field-effect mobilities of up to 0.016 cm(2) V-1 s(-1) and an on/off ratio of 1.4 x 10(5).