Metalloporphyrins for Quadratic Nonlinear Optics

Cu II - and Zn II -based donor−acceptor porphyrins have been examined for second-order nonlinear optics using the hyper-Rayleigh scattering technique at 1064 nm. Introduction of the metal ions enhances the first hyperpolarizability (β) of the free-base donor−acceptor porphyrins significantly. The open shell Cu II (d 9 ) has a greater influence on β of these porphyrin systems than the closed shell Zn II (d 10 ). The high β values in the Zn II porphyrins are understood in terms of the change in dipole moments upon excitation within the context of the two-state model as well as two-photon resonance enhancement. In Cu II porphyrin complexes a large number of excited states seem to contribute to β with, perhaps, a little contribution from two-photon resonance at the excitation wavelength.