Abstract
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.
Highlights
It is well known that electronic spectra of organic molecules in gas phase and in solution are different
Remarkable difference in λmax between water and other solvents was obtained when Solvent Accessible Surface (SAS) surface was used to construct the molecular cavity. These results suggest that proper description of atomic radii and molecular surface is one of key factors responsible for reproduction of experimental data
Quantum-chemical calculations have been performed for N,N-diethyl-4-nitroaniline in four common solvents using implicit and explicit solvents as well as combined approach
Summary
It is well known that electronic spectra of organic molecules in gas phase and in solution are different. Some recent examples include works using classical MD or MC methods [7,8,9,10,11,12,13,14,15,16,17] or ab initio molecular dynamics [18,19,20,21,22,23] Both implicit and explicit solvent models may be combined: few solvent molecules closest to the solute are treated explicitly and the whole system is embedded in a continuous solvent. Specific interactions between solute and explicit solvent molecules may be accounted for and the implicit solvent provides corrections originating from the bulk medium with computational cost significantly lower than in fully explicit models For these reasons, the mixed approach is quite often used in quantum-chemical calculations [15, 24,25,26].
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