Steering molecular dipoles from centrosymmetric to a noncentrosymmetric and SHG active assembly using remote functionality and complexation

Abstract

Utilization of flexible pendant groups bearing a remote functionality and complexation with an appropriate partner leading to the fabrication of a noncentrosymmetric molecular crystal lattice of interest in quadratic nonlinear optical applications is explored. 7,7-Diamino-8,8-dicyanoquinodimethane, which possesses a large molecular hyperpolarizability but shows an overriding tendency towards centrosymmetric crystal lattice formation, is chosen as a critical test case of a nonlinear optical chromophore. N,N-Dimethylaminoethylene moieties attached to the amino groups of diaminodicyanoquinodimethane serve as the pendant groups and terephthalic acid as the complexing partner. Parallel investigation of the crystal structures of the pure chromophore and its complex demonstrates the crucial role of the pendant group and the complexing partner in the formation of the noncentrosymmetric lattice of the complex with concomitant induction of optical second harmonic generation capability. This study suggests the possibility of developing a simple chemical approach towards the fabrication of acentric crystals for quadratic nonlinear optical applications.