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 oTPA-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 similar to 75% and similar to 19%, accompanied by red emission peaked around 600 nm.