Aggregation/deaggregation properties of ZnII Schiff-Base complexes and their applications as molecular probes, nonlinear optical materials and building blocks for new supramolecular architectures

Tetracoordinated bis(salicylaldiminato)ZnII Schiff-base complexes are Lewis acidic species which saturate their coordination sphere by coordinating a large variety of neutral or anionic substrates or in their absence, can be stabilized through intermolecular Zn…O axial coordination. 1H NMR, DOSY NMR, optical absorption and fluorescence spectroscopy studies indicate the existence of aggregate species in solutions of non-coordinating solvents. The type and the degree of aggregation are related to the nature of the bridging diamine. In coordinating solvents or in the presence of coordinating species, a complete deaggregation of the complexes occurs, because of the axial coordination to the ZnII ion. This process involves considerable changes of the 1H NMR, optical absorption, fluorescence and NLO properties and is strongly dependent of the Lewis basicity of the coordinating species, allowing their application as NLO materials, molecular probes and reference Lewis acids. Moreover, the appropriate functionalization of the Schiff-base ligands possessing flexible Lewis donor atoms as side substituents, offers the advantage to achieve new tailored ZnII supramolecular architectures.