Multi‐Resonance Thermally Activated Delayed Fluorescence Materials Based on Heteroatoms‐Incorporated Phenazine Derivatives and Di[2.2]Paracyclophane

Abstract Multi‐resonance thermally activated delayed fluorescence (MR‐TADF) materials have emerged as a focal point of research in organic light‐emitting diodes (OLEDs) owing to their exceptional optoelectronic characteristics. Herein, four MR‐TADF molecules based on boron/nitrogen skeletons and di[2.2]paracyclophane unit are reported. The introduction of heteroatoms (O, S, and Se) into the MR‐TADF molecules is achieved through the mono‐substitution of tert ‐butylcarbazole in the boron/nitrogen skeletons with heterocyclic compounds, including phenoxazine, phenothiazine, and phenoselenazine, resulting in a red‐shift of the emission peak from 480 to 509 nm and close‐to‐unity photoluminescence quantum yields. But as the atomic radius of the heteroatoms increased, the full width at half maximum of the spectrum expands from 24 to 49 nm. The exceptional performances of the emitters, which possess a peripherally protected extended MR framework, are attributed to the enhanced spin‐orbit coupling matrix elements arising from π‐conjugation and heavy‐atom effect, yielding maximum external quantum efficiencies exceeding 30% in their OLEDs. This work presents a molecular design strategy based on an asymmetrically peripheral protection strategy for constructing efficient MR‐TADF emitters for OLEDs.