An investigation of the role of the nature of sulfonate ancillary ligands on the strength and concentration dependence of the second order NLO responses in CHCl3 of Zn(II) complexes with 4,4'-trans-N5H4CH=CHC6H4NMe2 and 4,4'-trans,trans-NC5H4(CH=CH)2C6H4NMe2

To evidentiate the role of the nature of sulfonate ancillary ligands on the value of the quadratic hyperpolarizability of Zn(II) complexes with stilbazole-like ligands, the second-order nonlinear optical (NLO) properties of [ZnY2(4,4¢- trans-NC5H4CHdCHC6H4NMe2)2] complexes (Y ) CF3SO3, CH3SO3, or p-CH3C6H4SO3) are investigated. By working at relatively high concentrations (>3 ´ 10-4 M), the positive effect of the triflate ligand remains unique while, with nonfluorinated sulfonate ligands, the second-order NLO response is comparable to that of the related complexes with acetate or trifluoroacetate as ancillary ligands. However, at dilutions higher than 10-4 M, all of the sulfonate complexes reach huge quadratic hyperpolarizabilities because of solvolysis with the formation of cationic species such as [ZnY(4,4¢-trans-NC5H4CHdCHC6H4NMe2)2]+, characterized by a large second-order NLO response. This view is supported by careful conductivity measurements. The same behavior occurs if 4,4¢-trans-NC5H4CHdCHC6H4- NMe2 is substituted by 4,4¢-trans,trans-NC5H4(CHdCH)2C6H4NMe2.