Macromol. Chem. Phys. 「Most downloaded articles published in year 2005」

Macromol. Chem. Phys., 2005年12月19日 「Most downloaded articles published in year 2005」

An Electric Cyclophane: Cavity Control Based on the Rotation of a Paraphenylene by Redox Switching

H. Kanazawa, M. Higuchi, K. Yamamoto
J. Am. Chem. Soc. 2005, 127, 16404-16405.

An Electric Cyclophane:  Cavity Control Based on the Rotation of a Paraphenylene by Redox Switching

Although a free rotation around a single bond gives no mechanical output, it has let us imagine a molecular motor. A para-substituted aromatic ring can be regarded as a rotator with the para-rotation axis. When it is incorporated in a wider π-conjugated system, a quinoidal structure is generated accompanied by oxidation on the substituted groups at the 1,4-position, and the axis is fixed. A paraphenylenediamine was selected as the nanomechanical molecular module capable of locking and releasing the free rotation using an electrode in solution. We inserted the module into a simple molecular system, cyclophane. It was clarified that the cyclophane was able to open and close its cavity in a reversible redox process repeatedly.

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

T. Imaoka, R. Tanaka, S. Arimoto, M. Sakai, M. Fujii, K. Yamamoto
J. Am. Chem. Soc. 2005, 127, 13896-13905.

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

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 (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 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.

Metal-Assembling Dendrimers with a Triarylamine Core and Their Application to a Dye-Sensitized Solar Cell

N. Satoh, T. Nakashima, K. Yamamoto
J. Am. Chem. Soc. 2005, 127, 13030-13038.

Metal-Assembling Dendrimers with a Triarylamine Core and Their Application to a Dye-Sensitized Solar Cell

A series of charge-separable and hole-transporting phenylazomethine dendrimers with a triarylamine core are prepared and evaluated for use as a charge separator in dye-sensitized solar cells (DSSCs). Triphenylamine with dendric phenylazomethine (TPA-DPA) is prepared by synthesizing up to five generations of dendrons using a convergent method. The resultant dendrimer has a rigid sphere structure similar to globular protein, with a hydrodynamic radius of 2.43 nm. Electrochemical oxidation of the TPA core reveals that the dendron units in the dendrimer have 0.35 of the attenuation factor (β) in the electron transfer. Complexation of TPA-DPA with SnCl2 proceeds in stepwise fashion from the core to the terminal imine following the basicity gradient among imine groups in each dendron shell. DSSCs prepared by casting these dendrimers onto dye-sensitized TiO2 film exhibited a higher open-circuit voltage than the bare film through the suppression of back electron transfer. The generational growth of dendrons increases the radius of the dendrimer, resulting in a stronger association with I3- and higher open-circuit voltage with an increasing number of generations. Complexation with SnCl2 reduces the resistance of TPA-DPA and improves the fill factor. The energy conversion efficiency of the DSSC prepared using fifth-generation TPA-DPA is 21% higher than that for the bare film and, when complexed with SnCl2, provides a 34% improvement.

化学工業日報 「デンドリマーでカプセル材料」

飯塚 忠寿 (D3)

サブナノ粒子を用いた電極触媒反応の研究をしています。 月曜0時に週間少年ジャンプを読むのが毎週の楽しみです。合併号でお休みの週は元気がないです。