Geometry optimizations were performed for ground-state (GS), triplet-excited-state ( 3 ES) as well as for minimum energy crossing point of triplet and singlet multiplicities ( 1/3 MECP) of the [Re(CO)3(Pyta)(TPP)] + complex, depicted in Figure , using density functional theory (DFT). The B3LYP functional was employed in combination with the def2-SVP basis set for all atoms and the def2-ECP pseudopotential for the rhenium atom, in addition to this def2-TZVP was also used for benchmarking def2-SVP basis set (as shown in Table ). To account for solvation effects, the conductorlike polarizable continuum model (CPCM) was utilized with water as the solvent. Additionally, empirical dispersion corrections were included using Grimme's D3 version with Becke-Johnson damping. For the optimization of the triplet states ( 3 MLCT and 3 MC) and Frank-Condon excitation energy computation of MLCT state, unrestricted density functional theory (UDFT) and time-dependent density functional theory (TDDFT) was used, respectively; applying the same functional, basis sets, and computational setup as in the GS calculations. The Hessians of the local minima and transition state geometries were also computed with the same computational setup as that used for optimization. To connect the geometries of the 3 MLCT and 3 MC states, intrinsic reaction coordinate (IRC) calculations were performed. It is important to note that we selected B3LYP for the geometry optimizations in this study, as it has been shown to perform well for similar systems. Although we did not investigate the effect of using alternative functional, previous studies have emphasized that the choice of functional can significantly influence the accuracy, particularly in determining the relative stabilities of the 3 MLCT and 3 MC states. All the above-mentioned calculations were carried out using the Gaussian 16 program package. Nudge elastic Band (NEB) method was used find minimum energy path between MLCT and 3 MC state and to provide good guess for 3 TS geometries. The minimum energy crossing point (MECP) geometry between singlet and triplet state of the [Re(CO)3(Pyta)(TPP))] + complex was optimized with Harvey's algorithm as implemented on Orca 5.0 software package.