title: Probing stepwise complexation in phenylazomethine dendrimers by a metallo-porphyrin core.
abstract: A series of dendritic phenylazomethines (DPA), which have a meso-substituted zinc porphyrin core (DPAGX-ZnP, X = 1-4), were synthesized. Structural studies of these dendrimers were carried out using 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-like structure within a single-nanometer scale (R(h) = 22 A 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 relaxation times (T1). The DPAGX-ZnP acts as a multi-metal ion reservoir for SnCl2 and FeCl3. The generation-4 dendrimer (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-layer complexations from the inner imines nearest to the core to the surface. The redox behavior and fluorescence of the zinc porphyrin in these metal-assembled dendrimers also support the stepwise complexation of the metal ion. These analyses suggest that the finely assembled metal complexes in a dendrimer architecture strongly affect the electronic status of the porphyrin core. Results from transient absorption measurements strongly indicate a very fast electron transfer on a subpicosecond time scale between the core and assembled metal complexes.
authors.affiliation: Department of Chemistry, Faculty of Science and Technology, Keio University, Yokohama 223-8522, Japan.
authors.forename: Takane
authors.initials: T
authors.lastname: Imaoka
authors.forename: Reiko
authors.initials: R
authors.lastname: Tanaka
authors.forename: Sachiko
authors.initials: S
authors.lastname: Arimoto
authors.forename: Makoto
authors.initials: M
authors.lastname: Sakai
authors.forename: Masaaki
authors.initials: M
authors.lastname: Fujii
authors.forename: Kimihisa
authors.initials: K
authors.lastname: Yamamoto
mesh_terms: D001391:Azo Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D018360:Crystallography, X-Ray; D050091:Dendrimers / Q000737:chemistry*; D004563:Electrochemistry; D005456:Fluorescent Dyes / Q000737:chemistry; D008665:Metalloporphyrins / Q000138:chemical synthesis / Q000737:chemistry*; D008856:Microscopy, Fluorescence / Q000379:methods; D008958:Models, Molecular; D015394:Molecular Structure; D011166:Porphyrins / Q000138:chemical synthesis* / Q000737:chemistry; D013056:Spectrophotometry, Ultraviolet / Q000379:methods; D015032:Zinc / Q000737:chemistry*
chemical_list: D001391:Azo Compounds; D050091:Dendrimers; D005456:Fluorescent Dyes; D008665:Metalloporphyrins; D011166:Porphyrins; C506824:phenylazomethine; D015032:Zinc