Exploiting the helical motif for enhanced nonlinear optical response: hyperpolarizability of substituted m-phenylene oligomers

Abstract

There is considerable interest in developing organic systems for use in nonlinear optical (NLO) applications.1 The design strategy first involves the identification of a molecular candidate with a large hyperpolarizability, usually based on electronic factors. While many structural types have been studied, the most thoroughly examined systems involve push-pull substituted molecules with extended conjugation. Unfortunately, a sizable macroscopic susceptibility is not always obtained because of nonoptimal packing in the solid state. In centrosymmetric structures, the second harmonic generation is identically zero. While the problem can be overcome through poling or encapsulation in rigid polymeric matrixes, long-term thermal, photo, and oxidative stabilities are not easy to achieve.2 We now consider an integrated approach in which electronic and molecular structures work in concert. Molecules with an intrinsic preference for adopting helical structures, but which also permit sufficient delocalization, are suggested as promising candidates for NLO applications.