Abstract A brief outline is given of a new method for the calculation of electronic band-centre shifts of molecules in condensed phases. It is easy to implement using existing technologies, and is readily applicable to transitions involving from quite small to large degrees of charge transfer. A two-step process is involved: first, simulations are performed in order to determine the equilibrium structure of the medium around the chromophore. These configurations are then sampled and the frequency shift deduced using perturbation expansions of the quantum-chemical interactions. The method is applied here to the 1(n, π *) spectra of dilute pyridine in water. Observed thermodynamic and spectroscopic properties are reproduced.