Excited-State Properties of Some Thermally Activated Delayed Fluorescence Emitters: Quest for an Accurate and Reliable Computational Method

Thermally activated delayed fluorescence (TADF) finds application in organic light-emitting diodes. The molecules exhibiting TADF are characterized by small singlet-triplet energy gaps that help reverse intersystem crossing. Recently, ionization potential (IP)-tuned range-separated (RS) density functionals have been well accepted for studying excited-state properties. In the present work, two efficient descriptor-based tuning schemes [electron localization function (ELF) and Sol] of RS density functionals have been used to accurately reproduce the excited-state properties of TADF emitters by performing a single self-consistent field calculation. The lowest singlet vertical excitation energies (E-VA(S-1)) and the vertical singlet-triplet energy gaps (Delta E-VST) are computed with ELF-, Sol-, and IP-tuned RS functionals (LC-BLYP, omega B97, omega B97X, and omega B97XD). Encouraging mean absolute deviations from the experimental values with ELF*-, Sol*-, and IP-tuned functionals are observed. Consistent performance of the non-empirical tuned functionals is noted in different solvent dielectrics. In addition to these, fractional occupation calculations have shown that our tuned functionals almost satisfy the energy linearity curve. Thus, ELF*-and Sol*-tuned functionals are promising and reliable alternatives in computing the excited-state properties. Considering the small experimental singlet-triplet gap, we recommend ELF* to calculate E-VA(S-1) and Sol* to calculate Delta E-VS(T).

Automated summary

Thermally activated delayed fluorescence (TADF) has applications in organic light-emitting diodes. In this study, two efficient descriptor-based tuning schemes (ELF and Sol) were used to accurately compute the excited-state properties of TADF emitters. The results showed that these tuned functionals performed consistently in different solvent dielectrics and exhibited good accuracy in calculating small experimental singlet-triplet gaps.