Efficient Photoinduced Electron Transfer in a Porphyrin Tripod−Fullerene Supramolecular Complex via π−π Interactions in Nonpolar Media

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• 作者：Atsuro Takai ; Mohammed Chkounda ; Antoine Eggenspiller ; Claude P. Gros ; Mohammed Lachkar ; Jean-Michel Barbe ; Shunichi Fukuzumi
• 刊名：Journal of the American Chemical Society
• 出版年：2010
• 出版时间：March 31, 2010
• 年：2010
• 卷：132
• 期：12
• 页码：4477-4489
• 全文大小：553K
• 年卷期：v.132,no.12(March 31, 2010)
• ISSN：1520-5126

文摘

A novel porphyrin tripod (TPZn₃) was synthesized via “click chemistry”. Three porphyrin moieties of TPZn₃ are geometrically close and linked by a flexible linker. The electron-transfer oxidation of TPZn₃ results in intramolecular π-dimer formation between porphyrin moieties as indicated by electrochemical, vis−NIR, and ESR measurements. The cyclic voltammogram of TPZn₃ exhibited stepwise one-electron oxidation processes of three porphyrin moieties in the range from 0.58 to 0.73 V (vs SCE in CH₂Cl₂). When TPZn₃ was oxidized by tris(2,2′-bipyridyl)-ruthenium(III) ([Ru(bpy)₃]³⁺), the oxidized species (TPZn₃)ⁿ⁺ (0 < n ≤ 3) exhibited a charge resonance band in the NIR region due to the π-dimer formation between porphyrin moieties. A supramolecular electron donor−acceptor system was also constructed using TPZn₃. The flexible conformation of TPZn₃ makes it possible to capture a fullerene derivative containing a pyridine moiety (PyC₆₀) inside the cavity by π−π interactions as well as the coordination bond between Zn²⁺ and the pyridine moiety. The formation of a 1:1 supramolecular complex of TPZn₃ with PyC₆₀ (TPZn₃−PyC₆₀) was indicated in the UV−vis and ¹H NMR spectra in nonpolar solvents. The association constant of TPZn₃ with PyC₆₀ (1.1 × 10⁵ M⁻¹ in toluene) is much larger as compared with those of the corresponding monomer (MPZn) and dimer porphyrin (DPZn₂). The dynamics of photoinduced electron transfer from the singlet excited state of TPZn₃ to PyC₆₀ was examined by laser flash photolysis measurements. The efficient intracomplex photoinduced electron transfer in TPZn₃−PyC₆₀ occurred in nonpolar solvents, resulting from the π−π interactions between the porphyrin and fullerene moieties, together with intramolecular π-bond formation between the porphyrin radical cation and the neutral porphyrin in TPZn₃^•+.