Synthesis and characterization of novel 2,7-carbazole derivatives for blue light-emitting diodes

Abstract

Two 2,7-carbazole based low molecular weight derivatives, 9-hexyl-N ²,N ²,N ⁷,N ⁷-tetraphenyl-carbazole-2,7-diamine (TPCA) and 9′-hexyl-9′H-9,2′:7′,9″-tercarbazole (HTC), were synthesized by Buchwald and Ullmann coupling reactions, respectively. The optical, electrochemical and thermal properties of this two analogous small molecule hosts have been characterized. The HOMO level of TPCA and HTC were −5.25 and −5.29 eV indicating good hole-transporting properties. Both of the compounds emit deep blue light peaked at 410 and 428 nm in solid state. According to the measurement, the luminescence quantum yield of TPCA is 0.98, almost 1.7 times higher than that of HTC (0.59) in dilute THF solution. The geometrical and electronic properties of the compounds were studied using density functional theory calculations. The studies mentioned above indicate that both TPCA and HTC are suitable for active materials of blue light-emitting diodes.