Third-Order Nonlinear Optical Properties in Soluble Phthalocyanines with Tert-Butyl Substituents

Abstract

This paper reports on third-order nonlinear optical properties in various phthalocyanine compounds with tert-butyl peripheral substitution on each benzo ring at either the 2- or 3-position (tetra-tert-butyl-substituted isomer mixture). The third-order optical susceptibilities χ₁₁₁₁ ⁽³⁾(-3ω; ω, ω, ω)'s for the tetrakis(tert-butyl)phthalocyanine (TBPc) compounds were determined by optical third-harmonic generation measurements of spin-coated films at a wavelength of 1.907 µm. In each case, the third-order hyperpolarizability of the molecularly doped films is constant over the concentration of the TBPc's in polymethylmethacrylate. The χ⁽³⁾ values of the TBPc's are smaller than those of unsubstituted phthalocyanines. In particular, χ⁽³⁾ of tetrakis(tert-butyl)vanadylphthalocyanine (TBVOPc) is one order of magnitude smaller than that of VOPc. The origin of the large difference in χ⁽³⁾ values is discussed in terms of molecular packing.