Synthesis, aggregation behavior and nonlinear absorption properties of lead phthalocyanines substituted with siloxane chains

Abstract

The synthesis and characterization of polysiloxane substituted metal-free and lead phthalocyanines are described. These materials form a class of isotropic liquid phthalocyanines that combine a large nonlinear absorption with an exceptionally large nonlinear thermal refractive effect. These materials effectively couple the nonlinear absorption characteristics of the phthalocyanine (Pc) moiety with the thermorefractive properties typical of siloxanes. The room temperature index of these phthalocyanines can be varied by the choice of the siloxane substituent. Furthermore, the siloxane substituents are effective at inhibiting aggregation of the phthalocyanine rings. The observed aggregation constants in toluene solutions are very small and only a small degree of aggregation is observed even in the pure liquid phthalocyanines. Nonlinear transmission, z-scan, transient absorption and degenerate four-wave mixing studies confirm that the Pb substituted materials possess a broad spectral region of induced absorption with nonlinear absorption coefficients similar to that observed from other lead substituted phthalocyanines. The observed ground state molar absorption coefficients of the siloxy phthalocyanines are somewhat smaller than comparable alkyl substituted phthalocyanines. Taken together, these properties make these materials very useful for practical nonlinear optical applications. The coupling of siloxane chains to the Pc rings represents a promising way to achieve some important properties that are difficult to achieve by other means.