A red thermally activated delayed fluorescence emitter employing dipyridophenazine with a gradient multi-inductive effect to improve radiation efficiency

Developing efficient red thermally activated delayed fluorescence (TADF) emitters is a real challenge due to the serious nonradiation of their low-band-gap singlet charge transfer state. Dipyridophenazine (DPPZ) (weak electron-withdrawing pyridines fused with strong electron-withdrawing phenazine) is used as an acceptor to overcome this issue. The gradient multi-inductive effect of different heterocyclic units simultaneously enhances the intramolecular charge transfer for red emission of the TADF molecule o TPA-DPPZ , and facilitates the radiative transition of its singlet charge transfer state by increasing frontier molecular orbital overlap on the electron-deficient pyrazine moiety. The 10-fold increased oscillator strength of its singlet transition results in its excellent photoluminescence and electroluminescence quantum efficiencies of ∼75% and ∼19%, accompanied by red emission peaked around 600 nm. Red TADF emitter o TPA-DPPZ employs dipyridophenazine with gradient multi-inductive effect as acceptor, which enhances intramolecular charge transfer and radiative transition, resulting photo- and electro-luminescence quantum yields of 75% and 18.5%.