SHG Active Crystals of a Remote Functionalized Achiral NLO-phore Assembled through Zinc(II) Complexation

An achiral nonlinear optical chromophore with a “remote functionality” that can act as a ligand is developed on the
basis of 4-nitroaniline derivatized with pyridine. The molecules are assembled through complexation with simple
achiral zinc(II) salts and the H-bond network mediated by the counterions, to generate noncentrosymmetric materials
exhibiting optical second harmonic generation (SHG). The crystal structures of the new complexes are determined;
the counterion strongly influences the ligand orientations and lattice structure. SHG of the microcrystalline materials
is investigated. Correlation between the structure and SHG is rationalized using semiempirical quantum chemical
estimation of the hyperpolarizabilities of molecules and molecular clusters. The metal complexation plays a significant
role in molecular assembly but affects the SHG very little, enabling simplified analysis of the bulk property in terms
of molecular responses. Organization of remote functionalized molecules by metal ion complexation thus offers a
convenient approach to the rational design of quadratic NLO materials.