Once the MECP region of singlet and triplet state has been reached from the dissociative 3 MC5, the PES reaction will step into the final stage of reaction to form the stable photoproduct. The change in the geometrical parameters is nominal when we transit from 3 MC5 to 1/3 MECP, also the energy gap is nominal with a value of 0.03 eV, as shown in Figure and Table . This reflects the accessibility of MECP region from 3 MC5 is efficient which consequently leads to the dissociation of CO ligand. From the 1/3 MECP geometry the system dissociates further into the formation of a singletadduct, this shows the transition of the system from triplet-state to singletstate, as the system want to release the energy, as shown in Figure . The main change in the geometrical parameters of the transition from to Adduct is a huge elongation of 1.30 Å in R1 bond, the pyta ligand and other two COligands reach a planer structure, at this point the CO-ligand can be considered as completely dissociated from the complex. In Figure , we have also shown another geometry as, Penta, this singlet-penta-coordinated geometry reflects the formation point of the photoproduct when the CO-ligand is at a large distance from Re(I) atom i.e., 10 Å and at the same time the solvent ligand as acetonitrile is entering into the PLS reaction sphere. Finally, the stable photoproduct ([Re(CO)2(CH3CN)(Pyta)(TPP))] + + CO) is formed which is 0.35 eV higher in the energy profile than the reactant ([Re(CO)3(Pyta)(TPP))] + + CH3CN) of this PLS reaction.