Similarity and dissimilarity between water and methanol in solvent effects on the spectroscopic properties of aniline: Molecular dynamics and time-dependent DFT studies

Abstract

Solvent effects on the absorption spectra of aniline (C6H5NH2) are investigated. DFT and TD-DFT calculations for 1:1 aniline–water and aniline–methanol complexes predict that an N-bound isomer with an OH···N bond is the global minimum in the S0 state, while an H-bound isomer with an NH···O bond becomes lower in the S1 state. The N-bound and H-bound solvents cause blue and red shifts, respectively. MD simulations are used to allocate solvent molecules around aniline for constructing model structures with a complete solvation shell. TD-DFT calculations for the model structures are successful in reproducing the experimental observation that the absorption band in methanol is less blue-shifted than that in the water. At least one water molecule is incessantly bound to the nitrogen atom and causes the significant blue shift. In contrast, methanol molecules are less frequently bound to the nitrogen atom and therefore the blue-shifting effect is less significant.