A Rational Molecular Design Strategy of TADF Emitter for Achieving Device Efficiency Exceeding 36

An excellent thermally activated delayed fluorescence (TADF) emitter requires a sophisticated molecular design strategy to incorporate structural features to simultaneously achieve high photoluminescence quantum yield (PLQY) and high horizontal emission dipole ratio (Θ//). This work reports the uses of heteroarenes and dicarbonitrile benzenes to design four new acceptors PymCN, PyoCN, PmmCN, and PmoCN, which are linked to a common donor dimethylacridine (DMAC) for making new TADF emitters. The emission wavelength, ΔEST, krisc, kr, and the resulting PLQY of the target TADF emitters are governed by the combined natures of the heteroaryl bridges (Py vs Pm) and the CN‐substituted patterns (o‐CN vs m‐CN). The photophysical and device characteristics reveal the best acceptor to be PyoCN, which is further coupled with spiroacridine to afford a new emitter SpiroAC‐PyoCN with an enhanced PLQY of 100% compared to that (91%) of the DMAC‐based counterpart DMAC‐PyoCN. Furthermore, linking PyoCN with spiro‐bisacridine (SBAC) gives an A–D–A‐configured TADF emitter SBAC‐PyoCN with both enhanced PLQY (100%) and Θ// (90%). The device employing SBAC‐PyoCN as emitter renders a maximum external quantum efficiency up to 36.1% owing to its unity PLQY and superior light out‐coupling efficiency. This rational molecular design strategy provides a feasible means to achieve an excellent TADF emitter design. A rational strategy for designing thermally activated delayed fluorescence emitter is reported, using dimethylacridine as a common donor to select the acceptor PyoCN that comprises pyridine and ortho‐dicarbonitrile benezene. PyoCN links to rigid donors spiroacridine and spiro‐bisacridine, leading to high photoluminescence quantum yield and high horizontal emission dipole ratio. The best device accomplishes a maximum external quantum efficiency up to 36.1%.