NEAR-RESONANT CONTRIBUTION TO THE HYPERPOLARIZABILITY IN BENZOPORPHRINS

A theoretical investigation of the frequency-dependence of the second hyperpolarizability in the 400-750 nm spectral region is carried out f or model benzoporphrins using the sum over states method in conjunctio n with the random phase approximation and Pariser-Parr-Pople electron theory. The calculations examine the near-resonant contribution of one - and two-photon processes to the magnitude of the hyperpolarizability in the visible region of the spectrum. Results indicate that these on e- and two-photon processes are primarily determined by the nature of the low energy electron states of the benzoporphrin systems.