Strategic dihedral angle engineering for high-efficiency through-space charge transfer TADF emitters

Intramolecular through-space charge-transfer (TSCT)-enabled thermally activated delayed fluorescence (TADF) emitters have shown exceptional potential for advancing organic light-emitting diode (OLED) technologies, owing to their efficient utilization of triplet excitons and optimized photophysical properties. To date, the intrinsic correlation among molecular geometries, intramolecular non-covalent interactions, and photophysical properties in TSCT-TADF emitters remains unconfirmed, and this study theoretically clarifies this critical correlation. Specifically, through integrating molecular engineering, screening strategies, first-principles calculations, energy decomposition analysis, and statistical modeling, we systematically investigated 24 experimentally reported TADF molecules, and 54 newly designed structures in both solution and thin-film environments. We establish a clear geometric criterion for high-efficiency TSCT-TADF emitters: donor-acceptor (D-A) dihedral angles below 25° and interfragment distances within 4 Å—conditions validated by both theoretical predictions and experimental evidence. Based on this insight, we designed two novel molecular libraries with benzene- or carbazole-derivative bridges, using O-bridged triphenylamine (DPXZ) as the donor and quinolino[3,2,1-de]acridine-5,9-dione (QAO) as the acceptor. Our calculations confirm that sub-25° D-A dihedral angles correlate with exceptional delayed fluorescence efficiency, with predictions reaching up to 96% and an average of 70% for the new thin film systems. This study provides a rational design strategy for high-performance TSCT-TADF emitters, significantly advancing the molecular-level understanding of through-space interactions and accelerating the discovery of tailored, efficient OLED materials.