Probing Stepwise Complexation in Phenylazomethine Dendrimers by a Metallo-Porphyrin Core

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• 作者：Takane Imaoka ; Reiko Tanaka ; Sachiko Arimoto ; Makoto Sakai ; Masaaki Fujii ; and Kimihisa Yamamoto
• 刊名：Journal of the American Chemical Society
• 出版年：2005
• 出版时间：October 12, 2005
• 年：2005
• 卷：127
• 期：40
• 页码：13896 - 13905
• 全文大小：393K
• 年卷期：v.127,no.40(October 12, 2005)
• ISSN：1520-5126

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 (R_h = 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.