文摘
A series of dendritic phenylazomethines (DPA), which have a meso-substituted zinc porphyrincore (DPAGX-ZnP, X = 1-4), were synthesized. Structural studies of these dendrimers were carried outusing Tri-SEC (triple detection after size exclusion chromatography), intrinsic viscosity analysis, TEM(tunneling electron microscopy), and molecular modeling calculations by AM1. As a result, a sphere-likestructure within a single-nanometer scale (Rh = 22 Å for DPAG4-ZnP) was observed. In addition,encapsulating effects by the DPA shell in the larger dendrimers were confirmed as fundamental properties,based on the UV-vis abosorption spectra, cyclic voltammograms, and 1H NMR spin-lattice relaxationtimes (T1). The DPAGX-ZnP acts as a multi-metal ion reservoir for SnCl2 and FeCl3. The generation-4dendrimer (DPAG4-ZnP) can take up to 60 molar amounts of metal complexes around the porphyrin core.A quantitative study of the metal assembling reaction by UV-vis titration revealed stepwise layer-by-layercomplexations from the inner imines nearest to the core to the surface. The redox behavior and fluorescenceof the zinc porphyrin in these metal-assembled dendrimers also support the stepwise complexation of themetal ion. These analyses suggest that the finely assembled metal complexes in a dendrimer architecturestrongly affect the electronic status of the porphyrin core. Results from transient absorption measurementsstrongly indicate a very fast electron transfer on a subpicosecond time scale between the core andassembled metal complexes.