Effects of substituents on the intermolecular interaction, morphology, and charge transport of novel bis-lactam-based molecules

Abstract

To elucidate the origin of high charge carrier mobility in bis-lactam compounds with twisted geometries, we designed and synthesized a series of 3,7-diphenyl-1,5-dioctyl-1,5-naphthyridine-2,6-dione (NTDP) derivatives bearing various substituents (i.e., OCH₃, CH₃, H, F, and Cl) in the end-capping phenyl rings. Despite the distinct dihedral angle between the 1,5-naphthyridine-2,6-dione (NTD) core and the end-capping groups, all of the derivatives formed rigid molecular structures and the delocalized highest occupied molecular orbitals (HOMOs), which could lead to high charge transport properties. Among the derivatives, the fluorinated NTDP molecule (NTDP-F) exhibited the highest hole mobility of 0.54 cm² V⁻¹ s⁻¹ in vacuum-deposited organic field-effect transistors (OFETs) due to the strong intermolecular interaction, high crystallinity, and two-dimensional (2D) terrace-like morphology in the thin-film. Furthermore, the twisted geometry of NTDP-F allowed facile solution processability resulting in a high hole mobility of up to 0.27 cm² V⁻¹ s⁻¹ in solution-processed OFETs.