Dendritic polyphenylazomethines: Synthesis, structure, and metal-assembling function
Dendritic polyphenylazomethines (DPAs) were synthesized as novel topological polymer ligands with pi-conjugated structures by the convergent method via dehydration of aromatic ketones with aromatic amines in the presence of TiCl4. DPA G4 molecules are revealed to have a sphere-like structure with a 2.3-nm diameter and are regularly assembled without deformation of the molecule on a plate as observed by means of gel permeation chromatography (GPC), molecular modeling, transmission electron microscopy (TEM), atomic force microscopy (AFM), and pi-A measurements. The stepwise radial complexation in DPAs with SnCl2 was observed as a stepwise shift in the isosbestic point in the UV-vis spectra. The number of added equivalents of SnCl2 required to induce a shift was in agreement with the number of imine groups present in the different shells of the DPAs. These spectral changes suggest that the complexation is proceeding in a stepwise fashion from the core imines to the terminal imines of the DPAs, which was further supported by shell-selective reduction (SSR) of the imines.