Coordination assisted molecular assemblies of perylene-3,4,9,10-tetracarboxylic acid with copper (II) ion at the air/water interface

Perylene-3,4,9,10-tetracarboxylic acid (PTCA) was found to form stable Langmuir films at the air/water interface through the coordination with Cu(II) ion in the subphase although the compound itself could not form monolayer on a plain water surface. The Langmuir films can be transferred onto solid substrates by a Langmuir–Schaefer (LS) method. Surface pressure–area isotherm and measurement of the UV–Vis and FT-IR spectra of the transferred LS films confirmed the coordination between the carboxylic group and Cu(II) ion in the Langmuir films. Atomic force microscopy (AFM) measurements indicated that the Langmuir film was composed of small nanoparticles with a diameter of several tens of nanometers. X-ray diffraction (XRD) measurement on the transferred LS films revealed that the film formed a clear layer structure with a distance of 3.9 nm, which was in agreement with the height measurement from the AFM.