Figures 1 & 2 display the ground state optimizations of TAU and MTAU in water conducted using the B3LYP functional and the def2-TZVPD basis set. Following the optimization of the ground state geometry, we calculated the vertical excitation energies and assigned their respective electronic characters. Using the vertical excitation energies, the electron densities of the major molecular orbitals were calculated. Figures & display all the calculated electron densities for each compound using acetonitrile and water as the solvents. Table 1 presents all the vertical excitation energies calculated using the optimized ground state geometry. In Figure , the proposed Jablonski diagram showcases the accessible singlet and triplet electronic states in water. For excitation, there are two available: S 1 (ππ *) and S2 (ππ*), and three triplets lower in energy than the S 2 singlet available for intersystem crossing: T 3 (nπ*) ,T2 (ππ*), and T1 (ππ*). As previously explained, the character of each state was assigned by looking at the electron density of the Kohn-Sham orbitals contributing to each vertical transition. The Jablonski diagram included the highest spin-orbit coupling constant values obtained. The two highest values were 6.973 cm -1 (S2àT3) and 0.827 cm -1 (S1àT1). Table presents all the vertical excitation energies using the optimized ground state geometry. In Figure