We have divided this section into four subsections to discuss the PLS step-bystep from transition of the excited state from MLCT to MC state to the formation of the photoproduct. In Figure , the relative energies of 1 MLCT, MLCT, The characterization of electronic state MLCT is dictated by 5d orbitals of the rhenium atom and low-lying π and π* orbitals localized on the pyta ligand, as shown in Figure . Since the 3 MLCT state cannot be optically accessed from the electronic 1 GS, therefore, the initial photoactivation of the rhenium(I) complexes is to MLCT state (3.30 eV). Afterwards the MLCT state (2.68 eV) is populated via the intersystem crossing (ISC). Due to the presence of Re(I) atom, strong spin orbit coupling (SOCs) is induced, the ISC process is very efficient. The change of molecular geometry in this relaxation pathway of 3 MLCT state from 1 GS are nominal, as shown in Table1. The elongations of the Re-CO bond (R1, R2 and R3) are nominal and ranges from 0.03 -0.07 Å and in case of Re-P bond increase is just 0.01 Å. The contractions of the Re-N bond i.e., R4 and R5 are 0.07 Å and 0.16 Å, respectively is also observed. This relaxation is achievable within the Franck-Condon (FC) region. After the 3 MLCT is been populated, the PLS reaction begins, the first step of the reaction mechanism as bending of Re-COax (R1) bond. Usually to reach a 3 MC state from the MLCT state Re-CO bond is elongated continuously, as this is driven by the population of metalcentered antibonding orbitals in the ³MC state which weakens the axial bond, leading to elongation and facilitating CO dissociation. But we observed in the first step, to reach the 3 TS1, the R1 bond is first elongated by 0.23 Å and then to reach the 3 MC1 the R1 bond is bent and contracted by 0.09 Å, the information regarding the displacement vector of the 3 TS1 is shown in Figure . This step has been further verified with an intrinsic reaction coordinate (IRC) calculation to get a better insight into the energy barriers of this step, as shown in Figure . The quantitative spin density on Re(I) atom changes from 0.50 to 1.07 as we transit from MLCT to 3 MC1, as shown in Table . The other geometrical parameters of 3 MC1 geometry remains same, as shown in Table . As the total elongation in transitioning from 3MLCT to 3MC1 is merely 0.14 Å, we do not term 3 MC1 as dissociative metal-centered state.