Optimizing triazine-based thermally activated delayed fluorescence molecules for enhanced organic light-emitting diode applications.

In pursuit of efficient organic light-emitting materials, we employed a rational design strategy to develop eleven cyanotriazine-based donor-π-acceptor emitters for thermally activated delayed fluorescence (TADF) applications. A comprehensive computational investigation using DFT and TD-DFT methods was carried out to evaluate their geometric and optoelectronic properties. The designed molecules are based on 4,4'-(6-phenyl-1,3,5-triazine-2,4-diyl)dibenzonitrile, where the dibenzonitrile unit acts as an acceptor and various donor units are introduced via a phenyl π-linker. Steric interactions between the donor units and π-linker induce twisted donor-acceptor geometries, which are favorable for TADF. Initial screening based on vertical excitation energies identified eight promising candidates with singlet-triplet energy gaps (ΔEST) below 0.3 eV. These systems were further analyzed in terms of spin-orbit coupling matrix elements (SOCMEs) and reorganization energies, which govern reverse intersystem crossing (RISC). Among the studied molecules, TZCN-PXZ, TZCN-PTZ, and TZCN-ICbz exhibit particularly favorable combinations of small ΔEST and enhanced SOCME values, indicating efficient TADF behavior. While nearly orthogonal geometries promote strong HOMO-LUMO separation and minimal ΔEST, moderately twisted conformations (≈70°) provide an optimal balance between ΔEST reduction and spin-orbit coupling enhancement via LE-CT orbital mixing. These findings establish clear structure-property relationships and provide useful design guidelines for developing high-performance TADF emitters.