Molecular design of NLO active π-conjugated compounds

The intramolecular charge transfer through n-electron conjugation gives large optical nonlinearities in the molecular level, i.e., the third-order susceptibility χ⁽³⁾_ijkl(-ω ₄; ω₁,ω₂,ω₃) depends on the microscopic third-order polarizability γ_ijkl(-ω₄; ω₁,ω ₂,ω₃) of constituent molecular unit. We have focused our researches for long on the development of one-dimensional conducting polymers such as polythiophenes, polydiacetylenes and substituted polyphenylacetylenes, and of two-dimensional macrocyclic conjugated compounds such as annulenes and metallophthalocyanine derivatives. In this paper we will discuss the key factors for designing molecular structures and nonlinear optical properties; that is, the dimensionality and symmetry of molecules and/or molecular aggregates