Rational Design and Construction of Polymers with Large Second-Order Optical Nonlinearities. Synthetic Strategies for Enhanced Chromophore Number Densities and Frequency Doubling Temporal Stabilities

The performance characteristics of poled polymeric second harmonic generation materials are crucially dependent upon achieving high number densities of constituent chromophore entities and on maintaining poling-induced microstructural acentricity. This article reviews recent progress toward these goals. Systems discussed include chromophore-functionalized polyphenylene ether macromolecules with second harmonic coefficients (d33) as high as 65 × 10−9 esu, Tg = 173°C, and with superior temporal stability of poling-induced chromophore orientation. Also discussed are strategies for simultaneously poling and diepoxide cross-linking chromophore-functionalized poly(p-hydroxystyrene). The result is a significant improvement in the temporal stability of chromophore orientation. Finally, two approaches to chromophore immobilization are presented which involve highly cross-linkable epoxy matrices. In the first, chromophore molecules are embedded in a matrix which is simultaneously poled and thermally cured. In the second, a functionalized high-β chromophore is synthesized for use as a cross-linking matrix component.