Single-point calculations were also performed in the DFT-optimized ground state structure at the MP2 level of theory to calculate the relative energies among possible tautomers. The optimized ground state geometries were then used to calculate the vertical excitation energies (VEEs) and SOCs in water by implementation of the time-dependent DFT (TD-DFT) using the CAM-B3LYP, 28 ωB97X 29 and PBE0 functionals and the 6-311+G(d,p) basis set at TD-DFT level of theory. The character of each vertical transition and optimized structures was assigned based the magnitudes of the oscillator strengths and by visual inspection of the Kohn-Sham orbitals.