Phase Behaviors and 2D-3D Morphological Transition of Aromatic Schiff Base Derivatives in Organized Molecular Films

A novel aromatic Schiff base ligand has been designed and its interfacial phase behavior as well as its in situ coordination with Cu(II) ions on the surface of pure water was compared with those of the corresponding pre-synthesized Cu(II) complex. Surface pressure-area isotherms, ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, and atomic force microscopy were used to characterize deposited monolayer and multilayer films of the complexes. Both the ligand and corresponding complex formed stable monolayer or multilayer films at the air/water interface, which could be subsequently transferred onto solid substrates to construct Langmuir-Blodgett films. A novel phase transition was observed when the ligand was spread on the surface of pure water. During this phase transition, the two-dimensional (2D) flat film changed into three-dimensional (3D) fiber-like nanoarchitectures. However, upon coordination with Cu(II) ions, only flat films were obtained. This phenomenon was thought to be caused by the change of molecular conformation and/or hydrophobicity during supramolecular assembly at the air/water interface. This work provides a simple clue for regulating the nanostructures in organized films.