Controlled emission colors and singlet–triplet energy gaps of dihydrophenazine-based thermally activated delayed fluorescence emitters

Abstract

We have developed thermally activated delayed fluorescence (TADF) emitters containing 5,10-dihydrophenazine as an electron donor and various electron-acceptor units. The TADF emitters exhibit wide ranges of emission colors from green to orange, singlet–triplet energy gaps ΔE_ST of ∼0–0.19 eV, and delayed fluorescence lifetimes τ_d of 0.1–50 μs. An organic light-emitting diode containing one of the TADF emitters exhibits a maximum external quantum efficiency (EQE) of 12%, which is higher than those obtained with conventional fluorescent emitters. Time-resolved photoluminescence measurements of the compounds in a host matrix reveal that TADF makes a large contribution to the EQE of the devices. Our findings provide guidelines for modulating ΔE_ST and τ_d of TADF emitters.