Third-order nonlinear optical properties of phthalocyanines and related compounds

Abstract

The nonlinear optical properties (NLO) of Phthalocyanines (Pcs) and Subphthalocyanines (SubPcs) studied by Third Harmonic Generation (THG), Electric-Field Induced Second Harmonic Generation (EFISH) and Z-scan are reviewed. Experiments were performed in solution and thin films in order to investigate both, the microscopic and macroscopic nonlinear mechanisms. For the Pcs, the analysis of the dispersive behavior of (chi) <SUP>(3</SUP>) in vacuum evaporated films allowed for the identification of two-photon states. In addition, it has been observed at both, microscopic and macroscopic level, that the metal leads to enhancements in the nonlinear response, that are probably due to the presence of two-photon (d-d) levels. Measurements of nonlinear absorption (NLA) in Pcs at 1.064 micrometer have confirmed the contribution of two-photon states to the nonlinear response and also a strong dependence on the presence of the central metal ion. The SubPcs, on the other hand, have also shown second order NLO properties, since they are non-centrosymmetric. From Hyper-Rayleigh Scattering (HRS) experiments, large second-order molecular polarizabilities (beta) have been determined. Second order NLO response is also present at a macroscopic level, as measured in thin films by Second Harmonic Generation (SHG).