Chemical Strategies for Modifying Carbonyl/Nitrogen‐Based MR‐TADF Materials toward Narrowband Emission

Abstract The past decade has witnessed remarkable progress in multi‐resonance thermally activated delayed fluorescence (MR‐TADF) emitters based on nitrogen/carbonyl (N/C═O) frameworks, the quinolino[3,2,1‐de]acridine‐5,9‐dione (QAO) derivatives, with a focus on achieving narrowband emission for high‐performance OLED applications such as ultra‐HD displays. This review categorizes and analyzes structural modifications across four key molecular architectures—pristine QAOs, phenyl‐substituted QAOs, cyclized QAOs, and polynuclear QAOs—revealing their distinct impacts on full width at half maximum (FWHM), reorganization energy (λ), and excited‐state dynamics. Notably, structural strategies such as R 1 substitution, R 4 ‐R 5 cyclization, and steric shielding with bulky groups like tert‐butyl lead to enh anced molecular rigidity, suppressed vibrational relaxation, and record‐narrow emissions (FWHM ≤ 13 nm). Furthermore, donor‐acceptor tuning across the series enables precise the highest occupied molecular orbital (HOMO) – the lowest unoccupied molecular orbital (LUMO) separation, balancing short‐range charge transfer with emission color control. Emission statistics, fluorescence lifetime analysis, and device performance metrics are presented, consolidating structure‐property relationships across >100 reported derivatives. This review provides design principles grounded in both theoretical insight and empirical evidence, offering a roadmap for the development of next‐generation MR‐TADF materials with high color purity, stability, and efficiency. These findings highlight the N/C = O MR core as a versatile and promising scaffold for advanced display technologies.