Nonlinear optical properties of a two-level molecular system immersed in a thermal bath have been studied in the present work. Solvent effects were explicitly considered by modeling the non-radiative interaction with the solute as a random variable. The innovation of this treatment is that it allows us to take into account the environment, inducing quantum effects not considered by classical treatment. The major contribution of the methodology proposed in this work, is the implementation of an approximant to the Voigt function as a probability distribution, because it allow us to cover a wider range of possible interactions among the solvent and the molecular system by simple changing the parameters σL and σG, associated to the variances of the Lorentzian and Gaussian distributions, respectively.