Backbone‐Acceptor/Pendant‐Donor Strategy for Efficient Thermally Activated Delayed Fluorescence Conjugated Polymers with External Quantum Efficiency Close to 25% and Emission Peak at 608 nm

Abstract A feasible strategy, backbone‐acceptor and pendant‐donor, for constructing thermally activated delayed fluorescence (TADF) conjugated polymer is presented. In the obtained polymers PSAQFx, the backbone consists of dibenzothiophene‐S,S‐dioxide (S) and 6,7‐difluoroquinoxaline (QF), while two 9,10‐dihydroacridine (A) groups as pendants are grafted on QF acceptor through phenylene bridges. Compared to the model compound AQF, the polymers exhibit redshifted emission owing to extended conjugation along the acceptor backbone. Photoluminescence quantum yields can be improved by managing the molar content (x) of the AQF unit and reach the maximum of 91% for PSAQF5 in neat film. Solution‐processed organic light‐emitting diodes (OLEDs) using these polymers as the emitters achieve a maximum external quantum efficiency (EQE) of 24.8% and a maximum power efficiency of 68.5 lm W⁻¹ with the emission peak at 608 nm and luminance at 58 cd m⁻². This is the first example of achieving EQE above 20% with emission peak over 600 nm in the polymer TADF OLEDs.