The valence excitations of the three isomers of thiopyridone, in gas phase and solution, were computed using the TDDFT approach and the data is tabulated in Tables and, in the SI. Table also provides a comparison to CASSCF results for determining excited state properties. Each isomer presents two types of low-lying ππ * excitations, identified as ππ * 1 and ππ * 2 . The orbitals from the valence space of the isomers are illustrated in Figure . Similarly, the orbitals considered in the active space of the CASSCF computations are collected in Figure of the SI. The orbitals of ortho, meta, and para thiopyridone are essentially in a 1-to-1 homomorphous relationship. For all three isomers, both π * 1 and π * 2 have two nodes in the heteroaromatic ring, but the amplitude is gradually reoriented in the ring as the secondary amine group comes closer to the thione group. A similar effect is seen in Figure in the occupied π orbital, which however retains the symmetry around the thione group. The following discussion on the valence states focuses on four excitations from both singlet and triplet multiplicities: nπ * 1 , nπ * 2 , ππ * 1 , and ππ * 2 . These excitations are observed consistently across all three isomers in both gas-phase and solvated models. The tabulated data of the solvation models in Table demonstrate consistency in the evaluated singlet and triplet electronic features across the TP isomers. Although some discrepancies are evident between the models, they are insignificant. In the case of the implicit models, the TDDFT results collected from the two solvents (water and acetonitrile) are equivalent in terms of excitation energies and the underlying electronic structure. In contrast, the comparison with the gas phase model (see Table ) displays a small rise in the excitation energies of the solvated model of 2-TP. A state swap is also noticed when two adjacent states exist with comparable excitation energies. For instance, the swapping of T(nπ * 1 ) and T(ππ * 2 ) states from the 2-TP gas to 2-TP water impl . Here, the two triplet states display an energy separation of ≈0.15 eV. Similar solvatochromic shifts are noticed in the excitation energies across all three isomers. These shifts in the absorption energies can be attributed to variations in the state dipole moments(µ) of the ground and higher adiabatic states. For reference, subsection S1.1