Simple and accurate computations of solvatochromic shifts in pi ->pi* transitions of aromatic chromophores

A new approach is introduced for calculating the spectral shifts of the mos t bathochromic pi --> pi* transition of an aromatic chromophore in apolar e nvironments. As an example, perylene in solid and liquid n-alkane matrixes was chosen, and all shifts were calculated relative to one well-defined sol id-inclusion system. It was shown that a simple two-level treatment of the solute using Huckel theory yields spectral shifts in excellent agreement wi th experimental results for the most prominent inclusion sites of perylene in solid n-alkane surroundings and for the dilute solutions in liquid n-alk anes. The idea is general enough to be applied to any aromatic chromophore in a nonpolar solvent matrix. In contrast to earlier treatments, this appro ach is based on geometry- and environment-dependent polarizabilities, emplo ys an r(-4) dependence for the dispersion energy, and is conceptually very simple and computationally very efficient.