Effect of cyano substitution in TADF molecules on luminescence properties: a theoretical study

Wise design strategies for efficient thermally activated delayed fluorescence (TADF) molecules are highly desirable. In this work, the effect of cyano-substitution effects on the molecular photophysical properties of five TADF molecules was investigated. The energy gap (△EST), natural transition orbitals (NTOs) properties, the Huang-Rhys factor and reorganization energies, rate constants for the intersystem crossing (kISC) and reverse intersystem crossing (kRISC) are analyzed based on density functional theory (DFT) and time-dependent density functional theory (TD-DFT) in combination with the thermal vibration correlation function (TVCF) method to measure method. CzTrzBp-CN-4 has the smallest △EST and larger spin-orbital coupling (SOC) in the film, leading to larger kRISC, suggesting that the cyano connections between the acceptor and other acceptors can effectively increase the twist angle and promote the kRISC, predicting that it may have TADF properties.