SOLVENT EFFECTS ON THE MOLECULAR QUADRATIC HYPERPOLARIZABILITIES

The Self-Consistent Reaction-Field (SCRF) theory has been employed to compute the first hyperpolarizability of a series of organic chromophores in the presence of a solvent. The solvent effect has been included in a self-consistent fashion, and hence the effect of the solvent has been included in calculating all the properties of the chromophores, namely the transition energies, the oscillator strengths of the associated transitions, the dipole moments of all relevant states, and the hyperpolarizabilities. The quadratic hyperpolarizability has been computed using the correction vector method. The results are then compared with the previously reported values of the hyperpolarizability and the experimentally observed Second-Harmonic Generation (SHG) coefficients at an excitation energy of 0.65 eV. The results show a good agreement with the experimentally observed values for many of the molecules, although there may be some overestimation of the hyperpolarizability values in cases where the ground state dipole moment of the chromophore is large. The earlier calculations, in which only the shifts in the transition energies in the presence of the solvent were used to compute the hyperpolarizabilities of the chromophores, appears to slightly underestimate the solvent shifts. This can be attributed the neglect of the effect of the solvent on the oscillator strengths and the dipole moments of the various states, which occur in the numerator of the Sum Over States (SOS) expression.