Solvent effects on molecular spectra. III. Absorption to and emission from the lowest singlet (n,π*) state of dilute pyrimidine in water

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Abstract
A model is developed for the solvent shift of the center of an electronic absorption or emission band and is applied to the interpretation of the spectra of dilute pyrimidine in water. It is based on the use of standard simulation techniques such as molecular dynamics and Monte Carlo to calculate the liquid structure around the chromophore in its initial electronic state; the solvent shift is then deduced by considering the changes in the electrostatic distribution of the chromophore on vertical Franck–Condon excitation. During the solvent‐shift evaluation only, spherical boundary conditions are used and the sample, containing both the solute and a large number of explicitly polarizable solvent molecules, is placed inside a dielectric continuum. The results show that the solvent shifts of both the absorption and fluorescence spectra of pyrimidine in water are comprised of approximately equal contributions from specific hydrogen‐bonding interactions and long‐range–plus–nonspecific dipole solvation effects. The solvent shift is shown to be very sensitive to the structure of the liquid. A specific aim of our approach is to develop a method applicable to molecular electronic devices, and to inorganic complexes.