Isomeric model molecules: understanding and regulating the emission nature of multiple-resonance thermally activated delayed fluorescence.

Multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters exhibit high photoluminescence quantum yields and exceptional color purity, driving significant interest in high-performance organic light-emitting diode (OLED) applications. Current strategies for constructing full-color MR-TADF emitters rely on intricate structural designs to regulate emission wavelengths, yet overlook critical photophysical parameters (such as emission maximum, excited-state lifetime, and so on) and obscure fundamental structure-property relationships, impeding precise control over photophysical behaviours. To address this issue, this study adopts a unique isomeric design strategy to reveal the basic emission properties of MR-TADF molecules. By systematically probing subtle connectivity differences within conserved mono-boron and dual-boron-based multi-resonant skeletons, the chemical bonding pattern dependent emission property was investigated. The critical factors affecting emission wavelength and excited-state lifetime have been uncovered. The detailed theoretical analyses provided a reasonable explanation for these results. This study establishes a molecular design strategy for precise optimization of emission properties, offering deep insights to facilitate the development of high-performance MR-TADF materials. Moreover, the exceptional device performance of compounds -DABNA-Cz and -DABNA with high efficiency and satisfactory color purity demonstrates the practicality and significance of the developed method.