We will use two biochromophores as examples: oxyluciferin (OLU -), which gives rise to firefly's bioluminescence, and phydroxybenzyledene imidazolinone (pHBDI -), a synthesized analog of the chromophore in green fluorescence protein. For both chromophores, a single molecular anion is solvated in a rectangular box with around 1600 water molecules and a counter ion. From a 100 ps NVT simulations (at 300 K), 100 frames are collected at equal intervals. The canonical molecular orbitals (MOs) obtained from KS-DFT calculations 42-44 at the ωB97X-D/6-311++G(d,p) level for a representative configuration of either anionic chromophore together with 30 closest water molecules are shown in Fig. . One can see that HOMO and LUMO of both chromophore-water complexes are located mostly on the chromophore, with a small contribution from a couple of solvent molecules. In contrast, the LUMO+1 of pHBDI -is primarily localized on the solvent molecules with a small contribution from the chromophore. These are the key orbitals involved in the lowest-energy excitation of the respective solvated chromophore based on the time-dependent density functional theory within the Tamm-Dancoff approximation (TDDFT/TDA). Table : Weights of KS-DFT frontier orbitals of OLU -and pHBDI -, both in a representative solvent configuration with 30 water molecules. Full-system DFT calculations were performed using the ωB97X-D functional and 6-311++G(d,p) basis. Weights w and w ′ were computed in the standard and Löwdin-orthogonalized atomic basis, respectively. The subscript A refers to the chromophore, E the solvent molecules, and AE the chromophore-solvent coupling.