A series of novel host materials based on the 10,11-dihydro-5H-dibenzo[b,f]azepine unit for highly efficient green and red organic light-emitting diodes

Abstract

Three novel host materials (D-PY, S-CZ and S-TPA) based on the 10,11-dihydro-5H-dibenzo[b,f]azepine (AZ) motif were designed and synthesized. The donor groups, triphenylamine (TPA) and carbazole (CZ), were attached at different positions of the central core to study the effect of the variation of substructures on their photophysical properties and the device performance of organic light-emitting diodes (OLEDs). These host materials showed excellent thermal stability with glass transition temperatures (T_g) up to 137 °C and decomposition temperatures up to 452 °C. All three compounds demonstrated high triplet energy levels (>2.60 eV) and suitable frontier molecular orbital energy levels for green and red OLEDs. The red phosphorescent OLEDs hosted by D-PY showed the maximum external quantum efficiencies (EQEs) over 26%, and the green phosphorescent OLEDs hosted by S-TPA demonstrated a maximum current efficiency (CE) of 86.0 cd A⁻¹ and a maximum power efficiency (PE) of 86.7 lm W⁻¹. In addition, a small efficiency roll-off (2.6%) from the maximum value is observed for S-CZ-hosted red OLEDs with an EQE of 22.6 at 1000 cd m⁻². This work demonstrated a promising design strategy for host materials via the incorporation of the AZ unit to obtain highly efficient green and red OLEDs.