Showing papers by "Hiroshi Nishihara published in 2004"

Multi-Mode Molecular Switching Properties and Functions of Azo-Conjugated Metal Complexes

Abstract: Recent studies on the azo-group-combined photochromic metal complexes are reviewed. These studies show unique trans-cis isomerization behaviors that have not been observed in regular organic azobenzenes. In the case of azobenzene-bound bis(terpyridine) complexes of transition metals, photoisomerization behavior depends strongly on the central metals, counterions, and solvents. Rh and Co complexes undergo photoisomerization smoothly, but the isomerization of Ru and Fe complexes is substantially retarded due to the energy transfer from the π-π* excited state to the MLCT transition. The photoluminescence property of an azobenzene-attached Pt complex is switched by photoisomerization of the azo moiety. Tris(azobenzene-bound bipyridine)cobalt undergoes reversible trans-cis isomerization using a combination of the Co I I I /Co I I redox change and a single UV light source exciting the π-π* transition. The trans-cis conversion yield is higher for the meta isomer (with respect to the position of the azo group against the pyridyl group) than for the para isomer. The trans-cis photoisomerization behavior of a 6,6'-dimethyl-substituted azobenzene-bipyridine ligand is synchronized with coordination of the bipyridine moiety to copper. and the trans/cis isomerization can be controlled reversibly through Cu I I /Cu I redox and a single UV light irradiation. Photoreaction of azoferrocene occurs not only by UV-light irradiation but also by green light irradiation that excites the MLCT transition. 3-Ferrocenylazobenzene undergoes reversible trans-cis isomerization using a single green light source and the Fe I I I /Fe I I redox change. Azo-conjugated metalladithiolenes of Ni I I , Pd I I , and Pt I I with diphenylphosphinoethane as a co-ligand show facile photoisomerization. The energy of the reversible trans-to-cis photoisomerization is considerably lower than that of azobenzene. The thermal stability of the cis form is, however, much higher than that of the organic azobenzene derivatives showing similar low-energy trans-to-cis photoisomerization. A novel proton response of the azo group occurs, and the combination of photoisomerization and protonation leads to a novel proton-catalyzed cis-to-trans isomerization. These results indicate that several kinds of multi-photo-functionalities can be realized for the azo-conjugated transition metal complexes by tuning the interaction between the azo moiety and the metal complex unit.

Immobilization of Gold Nanoparticles onto Silicon Surfaces by Si−C Covalent Bonds

Abstract: A series of ω-alkene-1-thiol-stabilized gold nanoparticles were prepared by a wet process and then covalently linked to a hydrogen-terminated silicon(111) surface with Si−C bonds via a thermal hydrosilylation reaction. The modified silicon surfaces were observed mainly by high-resolution scanning electron microscopy (HR-SEM). The HR-SEM images revealed that the gold nanoparticles protected with 2-propene-1-thiol (C3) were covalently bound to the hydrogen-terminated silicon surface, after which the nanoparticles self-fused; on the other hand, gold nanoparticles protected with 5-hexene-1-thiol (C6) or 10-undecene-1-thiol (C11) were linked to the hydrogen-terminated silicon surface independently. These surfaces were stable in air and can be stored for several months without detectable decomposition.

Integrated waveguide gratings for wavelength-demultiplexing of free space waves from guided waves

Abstract: Optical waveguide demultiplexer was designed and fabricated by integration of two types of gratings, namely, guided-mode-selective focusing grating couplers (GMS-FGCs) and different-guided-mode-coupling distributed Bragg reflectors (DGM-DBRs) in a slab waveguide for constructing a wavelength-division-multiplexing chip-to-chip optical interconnecting board. In the waveguide demultiplexer, guided signal waves were separated wavelength-selectively by DGM-DBRs, and coupled out by GMS-FGCs to focused free space waves. Two-channel demultiplexing with 5-nm-wavelength spacing was demonstrated at around 850-nm wavelength.

Synthesis and physical properties of π-conjugated metallacycle polymers of cobalt and ruthenium

Abstract: Recent studies on two types of n-conjugated metallacylce polymers are reviewed. Reaction of CpCo(PPh 3 ) 2 with conjugated diacetylenes afford poly(arylene cobaltacyclopentadienylene) and that of CpRuBr(cod) does poly(arylene ruthenacyclopentrienylene)s in ambient conditions. Regioselectivity of the former metallacycling reacion is not perfect (at most 80% of the 2,5-diaryl selectivity) but that of the latter is satisfactory (∼100% of the 2,5-diaryl selectivity) for the formation of n-conjugated structure. Electrochemical oxidation of the cobaltacyclopentadiene polymer and reduction of the ruthenacycle polymer occur facilely and quasi-reversibly by the contribution of metal d-orbitals. Physical properties in undoped (neutral) and doped (charged) sates show the behavior of electronic band structure derived from the organic n-conjugated main chain strongly coupled with the metal d-orbitals. This affords, for example, photoconductivity in the neutral form of the cobaltacylopentadiene polymer and ferromagnetic interaction in the reduced form of the ruthenacyclopentatriene polymer.

Optical waveguide device for demultiplexing of free space waves from guided waves

Abstract: Optical waveguide demultiplexer for wavelength-division-multiplexing chip-to-chip optical interconnecting board was fabricated by integration of guided-mode-selective focusing grating couplers and different-mode-coupling distributed Bragg reflectors. Two-channel demultiplexing with 5-nm wavelength spacing was demonstrated.