Benchmarking TADF activity of sulfone based compounds

Thermally activated delayed fluorescence (TADF) mechanism can be explained as transfer of excitons from the first triplet excited state (T1) to the first singlet excited state (S1) by reverse intersystem crossing (RISC). In this study, the activity of sulfone-based TADF compounds was examined with descriptors by using density functional theory (DFT). Besides structural properties, photophysical properties of studied compounds were investigated. Dihedral angles obtained from optimized geometries are shown to change with respect to donor units. The nature of excited states was examined because of its impact on TADF efficiency. As seen in results, we can say that M062X functional is the only functional that gives locally excited (LE) character at triplet excitations. The energy difference between S1 and T1 excited states (∆EST ) is one of the analyzed descriptors and generated with three different functionals. The calculated ∆EST values are consistent with experimental values. To evaluate efficiency of functionals, the relationship of experimental kRISC with calculated 1/∆EST and spin-orbit coupling (SOC) that is required for reverse intersystem crossing (RISC) process is examined. As a result, B3LYP accidentally generates the best ∆EST values while M062X is the only functional that gives correct relationship between kRISC-SOC. According to comparison based on the effect of ∆EST and SOC values on the (R)ISC possibility (χ), M062X is the most reliable functional. The obtained visualization of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) and Φs indices are consistent with other descriptors. Finally, absorption and emission spectra are generated and compared with experimental spectra. The obtained results will have contributions to the selection of the most reliable functional and design strategies for TADF compounds.