In the context of the chromophores of the invention, the term ???nonlinear??? refers second order effects that arise from the nature of the polarizable chromophore (i.e., ???push-pull??? chromophore moieties) having the general structure D-??-A, where D is an electron donor group, A is an electron acceptor group, and ?? is a ??-bridge group that conjugates the donor group to the acceptor group.