Strategic Heavy‐Atom Engineering: Simultaneous Color Modulation and RISC Acceleration in MR‐TADF Systems

ABSTRACT Heavy‐atom effect has garnered significant interest in multi‐resonance thermally activated delayed fluorescent (MR‐TADF) emitters owing to its exceptional ability to enhance spin‐orbit coupling (SOC). However, systematic investigations into the impact of heavy‐atom configuration, including incorporation positions and quantities, remain limited. In this work, three chalcogen‐containing MR‐TADF emitters (BN‐OS, BN‐SS, and BN‐SO) are designed to elucidate the influence of chalcogen configuration on their luminescence behaviors. The emission colors are finely tuned through variations in atomic charge transfer characteristics, where an increased charge‐transfer distance induces a pronounced red‐shift in emission wavelength. Moreover, both the incorporation positions and quantities of heavy atoms significantly influence SOC, resulting in distinct reverse intersystem crossing (RISC) rates. Notably, increasing the quantity of S atoms from two to four in BN‐SS markedly strengthens SOC, leading to a 1.5‐fold enhancement in the RISC rate constant. Employing BN‐SS as the emitter, the device exhibits blue emission with a peak at 483 nm, reaches a maximum external quantum efficiency (EQE) of 33.7%, and retains an EQE of 20.8% at 1000 cd m −2 , superior to those of the other two molecules. These results validate the effectiveness of heavy‐atom configuration in regulating the luminescence properties and device performance of MR‐TADF emitters.