Katsuhiko Kanaizuka

Construction of Highly Oriented Crystalline Surface Coordination Polymers Composed of Copper Dithiooxamide Complexes

Layer-by-layer bottom-up crystal engineering of metal-organic crystals at the surface of sapphire or glass from organic (rubeanic acid and derivatives) and inorganic (Cu(2+)) components which when mixed in solution form instantly an amorphous solid with high proton conduction.

Photocurrent-Generating Properties of Organometallic Fullerene Molecules on an Electrode

Compact, rigid, five-legged fullerene derivatives C60R5Me and M(C60R5)Cp (M = Fe and Ru; R = C6H4COOH, C6H4C6H4COOH, and CH2COOH) were synthesized and arrayed on an indium-tin oxide (ITO) surface. These devices exhibit a respectable quantum yield with photocurrent generation up to 18%, and, more importantly, the direction of the photocurrent can be changed not only by the molecular structure itself but also by changing the geometric configuration of the photoactive acceptor (fullerene) and donor (metal atom) on the ITO surface.

Fabrication and Placement of a Ring Structure of Nanoparticles by a Laser-Induced Micronanobubble on a Gold Surface

We have developed a new fabrication method for a ring structure of assembled nanoparticles on a gold surface by the use of continuous Nd:YAG laser light. A micronanobubble on a gold surface, created by laser local heating, acts as a template for the formation of the ring structure. Both Marangoni convection flow and capillary flow around the micronanobubble are responsible for the driving force to assemble nanoparticles such as CdSe Q-dots into the ring structure from the solution. Because a single micronanobubble was generated by the Nd:YAG laser focusing point, the precise positioning of the ring structure was feasible directly on the gold surface, which makes it possible to fabricate various patterns of rings such as arrays and letters and even a double-ring structure without any photomasks or any templates.

Memory Effects in Molecular Films of Free‐Standing Rod‐Shaped Ruthenium Complexes on an Electrode

There is significant interest in exploring new informationstorage systems for molecule-based devices as an alternative to silicon-based dynamic random access memory (DRAM). The operational principle of a DRAM is based on storing charge on a capacitive metal oxide layer by applying a voltage and reading the charge as a bias current. These devices, however, rely on silicon-based technology, in which photolithographic manufacturing is reaching the lower size limit. Accordingly, as is the case for the development of nanoscale technologies to overcome the fabrication limit of siliconbased devices, molecular electronic devices are an emerging research subject. The formation of molecular self-assembled monolayers (SAMs) on surfaces is a promising bottomup approach for the fabrication of molecule-based elements such as switches, memories, and logic gates. In molecular switches, the injection or exclusion of charges should be activated or controlled by external signals such as electrical or photonic stimuli, and the change of potential gradient should be electrically transduced and transmitted to external circuits. 12–16] In molecular memories, the charge storage in the molecular layers can be used as a memory bit. Recently, many attempts to construct molecular memory devices have been reported. For example, metalloporphyrins attached chemically onto an electrode stored charges by oxidation or reduction; that is, writing was achieved by oxidation of a porphyrin SAM, and reading was achieved by sensing a current under open-circuit potential after the oxidation. As an another example, the use of successive potential gradients in electron-transfer reactions within a polymer containing both quinone and viologen moieties or in bilayer films composed of two polymers, namely, [M(phen)2(vbpy)] 2+

Glycine Crystallization in Solution by CW Laser-Induced Microbubble on Gold Thin Film Surface

We have developed a novel laser-induced crystallization method utilizing local heat-induced bubble/water interface. Continuous laser beam of 1064 nm is focused on a gold nanoparticles thin film surface covered with glycine supersaturated aqueous solution. Light absorption of the film due to localized plasmon resonance caused local heating at the focal position and produced a single thermal vapor microbubble, which generated thermal gradient followed by convection flow around the bubble and eventually induced glycine crystallization and growth. The crystallization mechanism is discussed by considering gathering and accumulating molecules around the bubble/water interface assisted by convection flow and temperature jump.

Preparation of electrochromic Prussian blue nanoparticles dispersible into various solvents for realisation of printed electronics

An insoluble solid of historic Prussian blue (PB) was transformed into dispersible PB nanoparticles in water and various hydrophilic and hydrophobic organic solvents. Via hybrid surface modification using Na4[FeII(CN)6] and short-chain alkylamines, the insoluble PB was successfully dispersed in hydrophilic-and-hydrophobic boundary alcohols, such as n-butanol. The n-butanol-dispersible PB nanoparticles afforded homogeneous spin-coated thin films on various substrates. The chemisorbed shorter-chain alkylamines, n-propylamines, of the PB nanoparticles were thermally released at 100 °C from their surfaces to present stubborn electrochromic PB thin films adhering to the substrate via mutual coordination-bonding networks.

Proton-induced tuning of metal-metal communication in rack-type dinuclear Ru complexes containing benzimidazolyl moieties.

Ru complexes bearing a bis-tridentate benzimidazolyl ligand have been synthesized. The dinuclear ones act as a bibasic acid with pK(a1)=4.36 and pK(a2)=5.90. The protonated form of the dinuclear complex exhibited two one-electron oxidations at +0.91 and +1.02 V versus the ferrocenium/ferrocene (Fc/Fc(+)) couple (the potential difference (ΔE)=0.11 V), but the di-deprotonated form showed two waves at +0.50 and +0.58 V versus Fc/Fc(+) (ΔE=0.08 V). Since the potential difference between two waves reflects the strength of the metal-metal interaction, the deprotonation of the benzimidazole moieties in the complexes weakened the Ru-Ru communication. The degree of electronic coupling between two metal centers, estimated from the intervalence charge transfer (IVCT) band, was greater for the protonated form. DFT calculations for the protonated and deprotonated forms of the dinuclear complex suggest that the Ru(II)-L(H(2)) π* interaction plays a key role in the Ru-Ru interaction.

Molecular Nanostamp Based on One-Dimensional Porphyrin Polymers

Surface design with unique functional molecules by a convenient one-pot treatment is an attractive project for the creation of smart molecular devices. We have employed a silane coupling reaction of porphyrin derivatives that form one-dimensional polymer wires on substrates. Our simple one-pot treatment of a substrate with porphyrin has successfully achieved the construction of nanoscale bamboo shoot structures. The nanoscale bamboo shoots on the substrates were characterized by atomic force microscopy (AFM), UV-vis spectra, and X-ray diffraction (XRD) measurements. The uneven and rigid nanoscale structure has been used as a stamp for constructing bamboo shoot structures of fullerene.

Largely enhanced photocurrent via gap-mode plasmon resonance by a nanocomposite layer of silver nanoparticles and porphyrin derivatives fabricated on an electrode

Photocurrent generation efficiency via the photoactive dyes, porphyrins, was strongly enhanced by construction of a nanocomposite structure, which consists of an undercoat layer of (3-mercaptopropyl)trimethoxysilane and densely and homogeneously attached silver nanoparticles on an electrode. The employed 5 -(4-carboxyphenyl)-10,15,20-triphenylporphyrins, 1, were embedded on the silver nanoparticle surface through their carboxylate moiety. The photo-absorption of 1 was significantly influenced by normal and gap-mode plasmon bands. The photocurrent of the nanocomposite structure was more strongly enhanced via the Q band excitation of 1, overlapped with the gap-mode plasmon band in the absorption wavelength range, and also showed stable photocurrent.

Grain-Boundary-Free Super-Proton Conduction of a Solution-Processed Prussian-Blue Nanoparticle Film

A porous crystal family has been explored as alternatives of Nafion films exhibiting super-proton conductivities of ≥10-2  S cm-1 . Here, the proton-conduction natures of a solution-processed film of nanoparticles (NPs) have been studied and compared to those of a Nafion film. A mono-particle film of Prussian-blue NPs is spontaneously formed on a self-assembled monolayer substrate by a one-step solution process. A low-temperature heating process of the densely packed, pinhole-free mono-particle NP film enables a maximum 105 -fold enhancement of proton conductivity, reaching ca. 10-1  S cm-1 . The apparent highest conductivity, compared to previously reported data of the porous crystal family, remains constant against humidity changes by an improved water-retention ability of the film. In our proposed mechanism, the high-performing solution-processed NP film suggests that heating leads to the self-restoration of hydrogen-bonding networks throughout their innumerable grain boundaries.