Spectral narrowing strategies in multiple resonance thermally activated delayed fluorescence materials

Multi‐resonance thermally activated delayed fluorescence (MR‐TADF) materials possess unique advantages of high‐efficiency and narrowband emission, which have rapidly occupied an important position in the field of organic light‐emitting diodes (OLEDs). In recent years, significant advancements have been made in the development of MR‐TADF materials, particularly in achieving spectral narrowing for high‐color‐purity OLED applications. Based on diverse MR‐TADF molecular skeletons, this review summarizes the primary molecular strategies to narrow spectrum by suppressing structural relaxation and intermolecular interactions. Key strategies include π‐conjugation extension, increased molecular rigidity, and the introduction of bulky substituents and intramolecular hydrogen bonds. Additionally, effects of these strategies on photophysical properties are discussed. These molecular design strategies are expected to offer valuable insights for the future design of high‐efficiency, narrowband OLED emitters.