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Takai, Atsuro,Chkounda, Mohammed,Eggenspiller, Antoine,Gros, Claude P.,Lachkar, Mohammed,Barbe, Jean-Michel,Fukuzumi, Shunichi American Chemical Society 2010 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.132 No.12
<P>A novel porphyrin tripod (TPZn<SUB>3</SUB>) was synthesized via “click chemistry”. Three porphyrin moieties of TPZn<SUB>3</SUB> are geometrically close and linked by a flexible linker. The electron-transfer oxidation of TPZn<SUB>3</SUB> results in intramolecular π-dimer formation between porphyrin moieties as indicated by electrochemical, vis−NIR, and ESR measurements. The cyclic voltammogram of TPZn<SUB>3</SUB> exhibited stepwise one-electron oxidation processes of three porphyrin moieties in the range from 0.58 to 0.73 V (vs SCE in CH<SUB>2</SUB>Cl<SUB>2</SUB>). When TPZn<SUB>3</SUB> was oxidized by tris(2,2′-bipyridyl)-ruthenium(III) ([Ru(bpy)<SUB>3</SUB>]<SUP>3+</SUP>), the oxidized species (TPZn<SUB>3</SUB>)<SUP><I>n</I>+</SUP> (0 < <I>n</I> ≤ 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 TPZn<SUB>3</SUB>. The flexible conformation of TPZn<SUB>3</SUB> makes it possible to capture a fullerene derivative containing a pyridine moiety (PyC<SUB>60</SUB>) inside the cavity by π−π interactions as well as the coordination bond between Zn<SUP>2+</SUP> and the pyridine moiety. The formation of a 1:1 supramolecular complex of TPZn<SUB>3</SUB> with PyC<SUB>60</SUB> (TPZn<SUB>3</SUB>−PyC<SUB>60</SUB>) was indicated in the UV−vis and <SUP>1</SUP>H NMR spectra in nonpolar solvents. The association constant of TPZn<SUB>3</SUB> with PyC<SUB>60</SUB> (1.1 × 10<SUP>5</SUP> M<SUP>−1</SUP> in toluene) is much larger as compared with those of the corresponding monomer (MPZn) and dimer porphyrin (DPZn<SUB>2</SUB>). The dynamics of photoinduced electron transfer from the singlet excited state of TPZn<SUB>3</SUB> to PyC<SUB>60</SUB> was examined by laser flash photolysis measurements. The efficient intracomplex photoinduced electron transfer in TPZn<SUB>3</SUB>−PyC<SUB>60</SUB> 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 TPZn<SUB>3</SUB><SUP>•+</SUP>.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2010/jacsat.2010.132.issue-12/ja100192x/production/images/medium/ja-2010-00192x_0019.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja100192x'>ACS Electronic Supporting Info</A></P>