Fast and accurate determination of the singlet-triplet gap in donor-acceptor and multiresonance TADF molecules by using hole-hole Tamm-Dancoff approximated density functional theory

• Main Authors: Woon, Kai Lin, Nikishau, Pavel A., Sini, Gjergji
• Format: Article
• Published: WILEY-V C H VERLAG GMBH 2022
• Subjects: QC Physics
• Online Access: http://eprints.um.edu.my/41714/

One of the requirements to design efficient emitters based on the multiresonance (MR)- or donor-acceptor (D-A) thermally activated delayed fluorescence (TADF) materials is a relatively small energy gap between the lowest singlet and triplet excited states (Delta E-ST). High-level ab initio calculations of their Delta E-ST provide benchmark results, but they are very time consuming and little practical for large-size systems. Here, the performances of hole-hole Tamm-Dancoff approximated density functional theory (hh-TDA-DFT) and the functional dependent accuracy of hh-TDA are examined on SE of a large number of MR- and D-A TADF molecules. The results indicate that hh-TDA combined with the hybrid functional B3LYP can predict Delta E-ST values for a wide number of MR-TADF molecules with mean absolute error (MAE) within 0.04 eV with correlation as high as 0.75. For D-A TADF molecules, Delta E-ST is less sensitive to the nature of the functionals, with MAE as low as 0.07 eV. The larger discrepancy between Delta E-ST obtained obtained from hh-TDA-DFT and experimental data in several oxygen-containing MR-TADF molecules is assumed to stem from the aggregation tendency of these compounds in solution. These findings provide important insights on the role of aggregation in reducing the Delta E-ST of of MR-TADF compounds.