Carbazole–pyrene derivatives for undoped organic light-emitting devices

Abstract

Two carbazole–pyrene derivatives, namely 3,6-dipyrenyl-9-(4′-tert-butylphenyl) carbazole (BPyC) and 3,6-dipyrenyl-9-(4′-pyrenylphenyl) carbazole (TPyC), have been designed and synthesized for application in organic light-emitting devices (OLEDs). While the two compounds have similar chemical structures and photoluminescent properties, OLEDs based on them show distinct electroluminescence (EL) spectra. The BPyC-based devices show a single peak saturated blue emission with CIE coordinates of (0.15, 0.18); whereas the TPyC-based devices exhibit two emission peaks at blue and yellow hues with CIE coordinates of (0.22, 0.29). The difference in their EL spectra is attributed to the substitution of the t-butyl unit of BPyC with a pyrenyl group to form TPyC, which effectively increases the electron-donating property and results in exciplex formation at its interface with the electron-accepting TPBI. A high external quantum efficiency of 3.11% is achieved in the TPyC-based devices. Influences of chemical structure and fluorescent quantum yield on the efficiency of exciplex emission are discussed.