Zinc Induced a Dramatic Enhancement of the Nonlinear Optical Properties of an Azo-Based Iminopyridine Ligand

An azobenzene based iminopyridine ligand 1 has been synthesized by a condensation reaction between N,N-dimethyl-4,4'-azodianiline and 2-formylpyridine. The complexation of the ligand with ZnCl2 afforded a tetrahedral neutral zinc metal complex (2) formulated as [(Azo-Imino-Py)ZnCl2]. The crystal structure analysis of the complex indicates the formation of a tetracoordinated zinc(II) ion with the expected tetrahedral geometry. In solid state, a 2D supramolecular architecture reinforced by pi-pi stacking and hydrogen bonding is observed. The UV-visible spectrophotometric titration studies of the ligand, by increasing amount of ZnCl2, confirm the existence of single complex species in solution. The nonlinear optical (NLO) investigations by Z-scan technique of both ligand 1 and complex 2 indicate a dramatic enhancement of the NLO absorption of the ligand upon complexation with ZnCl2. This enhancement is likely to be due to a large dipole moment found for the complex 2 as calculated by DFT/B3LYP methodology.