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

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.