Computational protocol for emission spectra and PLQY for thermally activated delayed fluorescence derived from sulfur/selenium-incorporated multi-resonant molecules

Full width at half maximum (FWHM) is an important indicator for color purity in molecular optical emission. In addition, brightness is determined by photoluminescence quantum efficiency (PLQY). Thermally activated delayed fluorescence (TADF) can convert the electro-pumped triplet states into emissive singlets. Especially, recent experiments suggest that multiple resonance TADF molecules doped with heavy atoms S/Se could effectively avoid the efficiency roll-off by promoting the reverse intersystem crossing (RISC) process. We propose a computational protocol to evaluate FWHM and PLQY based on quantum chemistry calculations and thermal vibration correlation function formalism, which is of great potential to design highly efficient and color-pure molecules. We further build a robust correlation between the reorganization energy of emission state λS1S0em with FWHM and the inverse of reorganization energy of the intersystem crossing (ISC) process 1/λS1T1 with experimental reverse ISC rate constant kRISCexp, crucial for TADF. Our computational method and findings can be used for the molecular design of organic light-emitting diode materials.