Relations Between Structure and Third-Order Nonlinearities of Molecules and Polymers

Organic materials with extended electron delocalization offer some perspectives to use their third-order nonlinearities in photonics [ 1 , 2 , 3 , 4 , 5 - 6 ]. Waveguide devices are especially attractive in this context [ 7 ]. Many compounds have been studied by means of third harmonic generation (THG) and described in reviews [ 8 - 10 ]. The question which structural factors primarily determine the magnitude of the nonlinear optical susceptibility χ (3) has basic importance. The strong influence of the π -electron derealization length L d was recognized early [ 11 , 12 ]. However additional possible influences on χ (3) exist, such as the dimensionality of the π -electron derealization, or the question, if compounds with heteroatoms like nitrogen or sulfur could lead to an increase of χ (3) [ 13 ].