A procedure based on the polarizable continuum model (PCM) has been applied to reproduce solvent effects on electronic spectra in connection with the time-dependent density functional theory (TD-DFT). To account for solute-solvent interactions, a suitable operator has been defined, which depends on the solute electronic density and can be used to modify the TD-DFT equations for the calculation of molecular polarizabilities and of electronic transition energies. The solute-solvent operator has been derived from a PCM approach depending on solute electrostatic potential: Recently, it has been shown that such an approach also provides an excellent treatment of the solute electronic charge lying far from the nuclei, being particularly reliable for this kind of applications. The method has been tested for formaldehyde in water and in diethyl-ether, and then applied to the calculation of solvent effects on the n --> pi* transition of diazabenzenes in different solvents. The computed transition energies are in fairly good agreement with experimental values.