Solvatochromic probe in molecular solvents: implicit versus explicit solvent model

Solvent-induced shifts in the absorption spectrum of N,N-diethyl-4-nitroaniline were studied by quantum-chemical methods in water, dimethylsulfoxide, acetonitrile and acetone. TDDFT methodology and semiempirical ZINDO/S and PM6-CIS approaches were used to calculate excitation energies. Solvent effect was modeled in implicit solvent model by different variants of the PCM approach. Classical molecular dynamics was applied to obtain solute-solvent geometries used in explicit solvent modeling. Most implicit solvent models fail to reproduce the sequence of solvatochromic shifts for four studied solvents, usually yielding too small effect for water. The best result of the PCM method was obtained with SMD atomic radii. Semiempirical quantum-chemical methods in explicit solvent model did not provide satisfactory description of solvatochromic shifts with the largest disagreement to experiment observed for water. TDDFT explicit solvent calculations performed the best in modeling of spectral shifts. Problems with reproduction of experimental data were attributed to specific interactions.