Multiphoton fluorescence free hyperpolarizabilities of subphthalocyanines

Subphthalocyanines have potential applications in the field of second-order nonlinear optics. However, multiphoton fluorescence has seriously complicated the accurate retrieval of their molecular first hyperpolarizability β by hyper-Rayleigh scattering. We report here hyper-Rayleigh scattering results on subphthalocyanines with experimental evidence of effective multiphoton fluorescence suppression. It is demonstrated that multiphoton fluorescence does indeed contribute to the scattering signal but that accurate values for the first hyperpolarizabilities can be deduced when taking this properly into account. More generally, this shows that experimental evidence of the absence of a multiphoton fluorescence contribution to hyper-Rayleigh scattering should be included whenever hyperpolarizability values of fluorescent compounds are reported.