論文リスト

学術論文 2008

Microfluidic Synthesis and Catalytic Application of PVP-Stabilized, ~1 nm Gold Clusters

Hironori Tsunoyama, Nobuyuki Ichikuni, Tatsuya Tsukuda*
Langmuir, 24, 11327-11330 (2008).

Microfluidic synthesis yielded PVP-stabilized, 1.3-nm gold clusters with narrower dispersity (σ=14%) than the conventional batch synthesis (σ=23%), which was due to homogeneous mixing of reductant and gold precursor on the molecular level. The highly monodisperse clusters exhibited higher catalytic activity for aerobic oxidation of p-hydroxybenzyl alcohol than batch-prepared clusters with the same average diameter due to the reduction of larger and less-active clusters in population.

Ubiquitous 8 and 29 kDa Gold:Alkanethiolate Cluster Compounds: Mass-Spectrometric Determination of Molecular Formulas and Structural Implications

Nirmalya K.Chaki, Yuichi Negishi, Hironori Tsunoyama, Yukatsu Shichibu, Tatsuya Tsukuda*
J. Am. Chem. Soc., 130, 8608-8610 (2008).

The molecular formulas and charge state distributions of thus-far known ubiquitous alkanethiolate-protected gold clusters with core-masses of 8 and 29 kDa were assessed using electrospray ionization mass spectrometry. The 8 and 29 kDa clusters were determined to be composed of single species, [Au38(SCn)24]z and [Au144(SCn)59]z, respectively, with charge states of z ≥ 0. Possible geometric structures for Au38(SCn)24 and Au144(SCn)59 are discussed, based on the structures of relevant systems that have been recently determined experimentally and theoretically: [Au25(SR)18] and Au102(SR)44, in which the Au cores are protected by monomers [-SR-Au-SR-] and/or dimers [-SR-Au-SR-Au-SR-]. Their preferential formation and chemical robustness are proposed as being associated with high stability due to geometric factors, while the Au-thiolate interface takes on common motifs regardless of the underlying Au core.

Ligand Exchange of Au25SG18 Leading to Functionalized Gold Clusters: Spectroscopy, Kinetics, and Luminescence

E. S. Shibu, M. A. Habeeb Muhammed, T. Tsukuda, T. Pradeep*
J. Phys. Chem. C, 112, 12168-12176 (2008).

Ligand exchange offers an effective way to modify the properties of the recently prepared quantum clusters of gold. To tune optical and photoluminescence properties of one of the most stable quantum clusters of gold, Au25SG18 (SG-glutathione thiolate), we functionalized it by the exchange of -SG with functionalized -SG and with an altogether different ligand, namely, 3-mercapto-2-butanol (MB). The products were characterized by various techniques such as optical absorption (UV-vis), Fourier-transform infrared (FT-IR), nuclear magnetic resonance (NMR), X-ray photoelectron (XPS), and luminescence spectroscopies, mass spectrometry, and thermogravimetry (TG). Analyses of the TG data helped to establish the molecular composition of the products. Ligand exchange reaction was monitored by NMR spectroscopy, and it was found that the exchange reaction follows a first order kinetics. The XPS study showed that after the exchange reaction there was no change in the chemical nature of the metal core and binding energy values of Au 4f7/2 and 4f5/2, which are similar in both the parent and the exchanged products. Photoluminescence studies of these clusters, done in the aerated conditions, showed that the excitation spectrum of the MB-exchanged product is entirely different from the acetyl- and formyl-glutathione exchanged products. The inherent fluorescence and solid-state emission of these clusters were observed. This intense emission allows optical imaging of the material in the solid state. The emission is strongly temperature dependent. The synthesis of a diverse variety of clusters and their chemical stability and intense luminescence offer numerous applications in areas such as energy transfer, sensors, biolabeling, and drug delivery.

Electronic Structure of Dendrimer-Au Hybrid Nanoparticles: Hard X-Ray Photoemission Study

Y. Murase, T. Kitagawa, M. Imamura, A. Tanaka,* H. Yasuda, Y. Negishi, T. Tsukuda, S. Ueda, Y. Yamashita, H. Yoshikawa, K. Kobayashi
Trans. MRS-J., 33, 169-172 (2008).

Luminescence Properties of Metallo-supramolecular Coordination Polymers Assembled from Pyridine Ring Functionalized Ditopic bis-Terpyridines and Ru(II) Ion

Fu She Han, Masayoshi Higuchi,* Taichi Ikeda, Yuichi Negishi, Tatsuya Tsukuda, Dirk G. Kurth
J. Mater. Chem., 18, 4555 - 4560 (2008).

We present the study of photophysical properties of several Ru(II)-based metallo-supramolecular coordination polymers (MEPEs) constructed from various ditopic bis-terpyridines (bis-tpy) bearing electron-rich (OMe) or electron-deficient (Br) groups at the 6-position of the pyridyl periphery and having different spacers for connecting the two tpy moieties. The MEPEs are distinct from the frequently reported analogues derived from unsubstituted tpy. The photophysical properties such as emission spectroscopic properties and lifetime at both room temperature and 77 K are presented. The MEPEs are luminescent at room temperature with quantum yields (Φlum) > 10−6 and lifetimes on a timescale of nanoseconds (τ = ca. 6.6−22.4 ns), and display strong luminescence at 77 K with Φlum = ca. 0.21-2.5 × 10−2 and lifetimes on a timescale of microseconds (τ = ca. 2.4-7.9 μs). More importantly, we find that introduction of either an electron-rich or an electron-deficient functional group at the 6-position of the ligands results in a clearly decreased absorption intensity of the derived MEPEs. This result is in contrast to the reported data in the literature where an increased intensity was observed when substitution occurred at the 4-position of tpys, regardless of the electron-rich or electron-deficient nature of the substituents. In accordance with the absorption behaviour, substitution at the 6-position also leads to a notably different effect on the luminescent properties of the complexes. Thus, our results provide an alternative strategy for the de novo design of new materials.

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