Synergetic Multiple Charge‐Transfer Excited States for Anti‐Quenching and Rapid Spin‐Flip Multi‐Resonance Thermally Activated Delayed Fluorescence Emitter

Abstract

Abstract The development of multiple resonances thermally activated delayed fluorescence (MR‐TADF) emitters exhibiting high efficiency, narrowband emission, rapid reverse intersystem crossing rate ( k RISC ), and suppressed concentration quenching simultaneously is of great significance yet a formidable challenge. Herein, an effective strategy is presented to realize the above target by synergizing multiple charge‐transfer excited states, including short‐range charge transfer (SRCT), through‐bond charge transfer (TBCT), and through‐space charge transfer (TSCT). The proof‐of‐concept emitter 4tCz2B exhibits a bright green emission with a narrow full width at half maximum (FWHM) of 21 nm (0.10 eV) in solution, high photoluminescence quantum yield of 97%, fast k RISC of 7.8 × 10 5 s −1 and significantly suppressed concentration quenching in film state. As a result, the sensitizer‐free organic light‐emitting diodes (OLEDs) achieve maximum external quantum efficiencies (EQE max S) of over 34.5% together with an unaltered emission peak at 508 nm and FWHM of 26 nm at doping concentrations ranging from 3 to 20 wt.%. Even at a doping ratio of 50 wt.%, EQE max is still as high as 25.5%. More importantly, the non‐sensitized devices exhibit significantly reduced efficiency roll‐offs, with a minimum value of 13.4% at a brightness of 1000 cd m −2 .