Theoretical investigation of nitrogen-linked poly(2,7-carbazole)s as hole-transport materials for organic light emitting diodes

Nitrogen-linked poly(2,7-carbazole)s, a novel class of carbazole polymers, are new organic light-emitting materials (OLEDs), which are capable of transporting holes. In this paper, the electronic properties of the neutral molecules, HOMO–LUMO gaps (ΔH–L), in addition to IPs and EAs, are studied using B3LYP functional. The lowest excitation energies (Eg) and the maximal absorption wavelength λabs are studied using the time dependent density functional theory (TDDFT). As a result of these calculations, the highest-occupied molecular orbital (HOMO) energies lift about 0.75–1.04 eV and thus the IP decrease about 0.52–0.74 eV compared to polycarbazole. This result suggested the significantly improved hole-accepting and transporting abilities of the nitrogen-linked poly(2,7-carbazole)s. Furthermore, the nitrogen-linked poly(2,7-carbazole)s also had longer maximal absorption wavelengths than polycarbazole.