We are currently working on the singlet triplet excitations using Time Dependent Density Functional Theory for the various photoluminescence applications (Phosphorescence, Delayed Fluorescence). Percentage of charge transfer and/or local excitations, nature of transitions (n-𝜋*, 𝜋-𝜋*) in. these excitations are investigated from the NTO (Natural Transition orbital) analysis. Along with TD-DFT we use ZORA (Zeroth Order Regular Approximation) which is a perturbative method for calculating Spin-orbit coupling matrix element between singlet and triplet excited states, which gives. a better understanding. in. the ISC (Intersystem Crossing) and RISC (Reverse Intersystem Crossing) rate constants between corresponding excited states.