Density Functional Vertical Self-Consistent Reaction Field Theory for Solvatochromism Studies of Solvent-Sensitive Dyes

Abstract

On the basis of the Franck−Condon principle, a density functional vertical self-consistent reaction field (VSCRF) solvation model for vertical excitation and emission processes is established. The principles and implementation of the VSCRF model are presented. The predicted blue shifts of the vertical excitation energies of diazines in different solvents from n-heptane to water solutions are compared with the corresponding time dependent density functional calculations and are in very good agreement with experiment. We have also applied this method to predict the blue shifts and the vertical excitation and emission energies of Brooker's merocyanine dye with increasing solvent polarities from CHCl3 to H2O solutions. Overall, our calculations predicted the relative excitation and emission energy orderings for Brooker's merocyanine in different solvents with different polarities. Also, the calculated Stokes shift is fairly well represented for different solvents, and the calculations correctly show that the absorption energies have a much stronger solvent dependence than the emission energies. The importance of both relaxation of the molecular structures and consideration of explicit H-bonding H2O and CH3OH molecules in water and methanol solvents in predicting the solvatochromic shifts is also discussed.