A Theoretical Study of Solvent Effects on the Structure and UV-vis Spectroscopy of 3-Hydroxyflavone (3-HF) and Some Simplified Molecular Models

Solvent effects on the UV-vis spectra of 3-hydroxyflavoneand other structurally related molecules (3-hydroxychromen-4-one,3-hydroxy-4-pyrone, and 4-pyrone) have been studied by combining time-dependentdensity functional theory (TDDFT) and the polarizable continuum method(PCM). Among the first five excited states of the four consideredmolecules, electronic states of n -> pi* and pi ->pi* nature appear. In general, the stability of the n ->pi* states decreases as the pi space becomes larger in sucha way that only for 4-pyrone and 3-hydroxy-4-pyrone are they the firstexcited states. In addition, they become less stabilized in ethanolsolution than the ground state, and this causes blueshift transitionsin solution. The opposite trend is found for the pi ->pi* excited states. They are less energetic with the pi-systemsize and when passing from gas phase to solution. The solvent shiftalso depends strongly on the size of the pi systems and on theformation of an intramolecular hydrogen bond; thus, it decreases whengoing from 4-pyrone to 3-hydroxyflavone. The performance of the threeversions (cLR, cLR(2), and IBSF) of the specific-state PCMmethod in predicting transition energies are compared.