Rigid phenanthro[4,5-abc]phenazine-cored iridium(III) complexes for high-performance near-infrared emission at about 800 nm in solution-processed OLEDs

Abstract

Simultaneously achieving high-efficiency and long-wavelength emission in near-infrared (NIR)-emitting iridium(III) complexes remains a huge challenge yet due to non-radiative decay of their susceptible excited states according to the energy-gap law. Herein, three new NIR-emitting iridium(III) complexes, namely TPAIr, HTIr and DPTAIr with donor-acceptor-donor (D-A-D) cheating architecture, are rationally designed and synthesized to address this issue. In these complexes, π-extended and electron-deficient phenanthro[4,5-abc]phenazine (PPz) are employed as the rigid acceptor core. Triphenylamine (TPA), n-hexylthiophene (HT) and diphenyl thiophen-2-amine (DPTA) are used as peripheral donor units, respectively. The effect of donor types on their photophysical, electrochemical and electroluminescent properties is primarily studied. It is found that the combined effect of the rigid central acceptor and peripheral donors together endow these complexes with high photoluminescence quantum yield (PLQYs) and a variational wavelength. Real NIR emission from 774 to 798 nm with PLQYs of 9–15 % and decay lifetimes as short as 0.32 μs are observed in solutions. Solution-processed organic light-emitting diodes with DPTAIr as an emitter reveals an intense NIR emission at 800 nm with an outstanding EQE of 2.98 % and a high radiance of 17,083 mW Sr−1 m−2. More importantly, the efficiency roll-off is efficiently alleviated in the devices at high current density. Our study provides a feasible molecular design strategy to develop NIR phosphors for long-wavelength, highly efficient and small efficiency roll-off NIR-OLEDs.