Controlling the Molecular Self-Assembly into Nanofibers of Amphiphilic Zinc(II) Salophen Complexes

The synthesis, characterization, and aggregation properties in the solid state of a series of amphiphilic Zn(salophen) Schiff-base complexes are presented, through a combined FE-SEM/XRD approach. It is found that these complexes self-assemble into nanofibers depending on the solvent used to prepare the solutions. Thus, fibrous aggregates are obtained from solutions of weak and volatile Lewis base solvents, either by drop-casting or by complete solvent evaporation, whereas, in the case of noncoordinating solvents, where oligomeric aggregates are already present in solution, no formation of nanofibers is observed. The length of side alkyl groups and their degree of interdigitation lead to a 2D columnar square structure in the case of the complex with the short 4-ethyloxy substituents, whereas complexes having longer 4-alkyloxy chains are characterized by a lamellar structure. Bundles of twisted nanofibers are formed by further interactions and interdigitation of the outside alkyl groups of each nanofiber. A simple model, which describes the mechanism of formation and structure of these nanofibers, is presented.