Kaname Yoshida

Nanoporous Nanorods Fabricated by Coordination Modulation and Oriented Attachment Growth

A growing attachment: Porous coordination polymer (PCP) nanorods are synthesized by modulation of the coordination equilibria between framework components, which regulates the rate of framework extension and crystal growth. Investigation of the crystal growth mechanism by TEM indicates that face-selective modulation on the surfaces of PCP crystals enhances the anisotropic crystal growth of nanorods by an oriented attachment mechanism.

Supramolecular donor-acceptor heterojunctions by vectorial stepwise assembly of porphyrins and coordination-bonded fullerene arrays for photocurrent generation.

A novel strategy for constructing a vertical arrangement of bicontinuous donor-acceptor arrays on a semiconducting electrode has been developed. The relationship between the film structure and the photoelectrochemical properties has been elucidated as a function of the number of donor layers for the first time. The maximum incident photon-to-current efficiency value (21%) is comparable to the highest value (20%) reported for vertical arrangements of bicontinuous donor-acceptor arrays on electrodes.

Self-Assembly Made Durable: Water-Repellent Materials Formed by Cross-Linking Fullerene Derivatives

Fullerene flakes: A diacetylene-functionalized fullerene derivative self-organizes into flakelike microparticles (see picture). Both the diacetylene and C(60) moieties can be effectively cross-linked, which leads to supramolecular materials with remarkable resistivity to solvent, heat, and mechanical stress. Moreover, the surface of the cross-linked flakelike objects is highly durable and water-repellent.

Superstructures and superhydrophobic property in hierarchical organized architectures of fullerenes bearing long alkyl tails

Formation of hierarchically self-organized architectures in organic media and their non-wetting surface features of a series of fullerene-C60 derivatives bearing different numbers of long hydrocarbon chains (1–3) and semiperfluoro-alkyl tails (4) are investigated by means of a variety of techniques, including X-ray diffraction, differential scanning calorimetry, as well as spectroscopic and microscopic methods. All derivatives self-assemble into a bilayer arrangement with their fundamental structural subunit and lamellar distance ranging from 2.88 to 4.85 nm depending on the substituents. The hydrocarbon-C60 derivatives (1–3) provide well-defined three-dimensional microparticles having a nanoflaked outer surface morphology or microparticles composed of many plate-like units in 1,4-dioxane solution, both architectures enhancing the surface water-repellency. The microparticles with a nanoflaked-outer surface obtained from a C60 derivative with semiperfluoro-alkyl chains (4) in a diethoxyethane solution exhibit a surface water-repellency comparable to objects formed from the hydrocarbon-hybrid C60 derivatives. Taking into account the moderate hydrophobic nature of the C60 surface compared to the high hydrophobicity of the hydro- or fluoro-carbons, these results suggest that the C60 moieties are exposed to the outer surface in the supramolecular objects formed in polar solvent conditions and define their non-wetting properties.

Substituent effects of porphyrins on structures and photophysical properties of amphiphilic porphyrin aggregates.

Substituent effects of porphyrin on the structures and photophysical properties of the J-aggregates of protonated 5-(4-alkoxyphenyl)-10,15,20-tris(4-sulfonatophenyl)porphyrin have been examined for the first time. Selective formation of the porphyrin J-aggregate was attained when suitable length of the alkoxy group was employed for the amphiphilic porphyrin. Namely, a regular leaflike structure was observed for the J-aggregates of protonated 5-(4-octyloxyphenyl)-10,15,20-tris(4-sulfonatophenyl)porphyrin, which was consistent with the results obtained by using the UV-visible absorption and dynamic light-scattering measurements. A bilayer structure in which the hydrophobic alkoxyl groups facing inside the bilayer are interdigitated to each other, whereas the hydrophilic porphyrin moieties are exposed outside, was proposed to explain the unique porphyrin J-aggregate. Fast energy migration and efficient quenching by defect site in the J-aggregates were suggested to rationalize the short lifetimes of the excited J-aggregates.

Photophysics and photoelectrochemical properties of nanohybrids consisting of fullerene-encapsulated single-walled carbon nanotubes and poly(3-hexylthiophene)

Novel nanohybrids of single-walled carbon nanotubes (SWNTs) encapsulating C60 or C70 with poly(3-hexylthiophene) (P3HT) have been prepared and their photophysics and photoelectrochemical properties are studied in detail for the first time. Strong π–π interaction between the SWNT sidewalls and P3HT afforded successful dissolution of the so-called fullerene peapods into an organic solvent, as in the case of empty SWNTs (p-SWNTs). Fluorescence emission of P3HT in the SWNT–P3HT hybrids was completely quenched by the SWNTs regardless of the fullerenes insertion. Transient absorption and fluorescence up-conversion techniques revealed the excited state dynamics of the nanohybrids, where exciplex formation from the short-lived P3HT singlet excited state (∼0.2 ps) with the fullerene peapods and subsequent relaxation to the ground state within ∼1 ps occurred dominantly. Significant difference in the photodynamics upon encapsulation of C60 or C70 was not detected, implying little participation of the fullerenes in the excited state event and thus the inability of the encapsulated fullerenes to generate the charge-separated state between the fullerene peapods and P3HT. Photoelectrochemical devices based on the peapod–P3HT nanohybrids showed almost the same incident photon-to-current efficiencies as those for the p-SWNT–P3HT-based device, which is in good agreement with the results of the time-resolved spectroscopies. Thus, the results obtained here will give a deep insight into the photophysics and photoelectrochemical properties of fullerene peapod–conjugated polymer as well as SWNT–conjugated polymer hybrids and therefore provide valuable information on the design of peapod-based optoelectronic devices.

Sol−Gel Synthesis of Low-Dimensional Silica within Coordination Nanochannels

Sol-gel condensation of tetramethoxysilane (TMOS) inside the channels of a coordination pillared layer structure [Cu2(pzdc)2(dpe)]n (1a; pzdc = pyrazine-2,3-dicarboxylate, dpe = 1,2-di(4-pyridyl)ethylene) produced subnanosized silica dispersed within the host framework. In this system, the growth of silica is effectively constrained, and the resultant silica shows a drastic decrease of its crystallization temperature because of its minute size.

Light Harvesting and Energy Transfer in Multiporphyrin‐Modified CdSe Nanoparticles

Multiporphyrin-modified CdSe nanoparticles (CdSe-H2P) were prepared to elucidate the interaction between chromophores and luminescent semiconducting nanoparticles in the excited and ground states. The CdSe-H2P nanoparticles were obtained by place-exchange reactions of hexadecylamine-thiophenol-modified CdSe nanoparticles with porphyrin alkanethiols in toluene. The number of porphyrin molecules on the surface of a single CdSe nanoparticle increased with increasing reaction time to reach a saturated maximum of 21. The porphyrins as well as the core in CdSe-H2P can absorb UV/Vis radiation. Steady-state emission and emission-lifetime measurements reveal efficient energy transfer from the CdSe excited state to the porphyrins in the CdSe-H2P nanoparticles. The resulting porphyrin excited singlet state is not quenched by the CdSe core. These unique properties are in sharp contrast with those of multiporphyrin-modified metal and silica nanoparticles. Thus, semiconducting nanoparticle-multiporphyrin composites are highly promising as novel artificial photosynthetic materials.

Assembly of carbon nanotubes and alkylated fullerenes: nanocarbon hybrid towards photovoltaic applications

Taking advantage of the non-covalent interaction between alkyl chains and the sidewalls of a single-walled carbon nanotube (SWCNT), a nanocarbon hybrid of SWCNT and a fullerene (C60) derivative with long alkyl chains was constructed as a donor–acceptor pair for photovoltaics and nanodevice investigations. It was found that SWCNT could be mostly unbundled by the alkylated C60 (1) and was well-dispersed in organic solvents. As a photoactive material, the resultant nanocarbon hybrid, 1-SWCNT, performed well in light-energy harvesting applications in photoelectrochemical cells and nanoscale field-effect transistors (FET). Moreover, the 1-SWCNT assembly exhibited superhydrophobicity, providing an interesting opportunity to fabricate nanocarbon-based waterproof optoelectronic devices. In order to understand the photoexcitation process, the 1-SWCNT assembly was electrochemically and spectroscopically characterized. The electrochemical results showed that the SWCNT facilitated electronic communication between 1 and the electrode. The steady-state and time-resolved fluorescence and the photoluminescence excitation studies suggested efficient quenching of the singlet excited state of C60. Nanosecond transient absorption data revealed the one-electron reduction of fullerene, C60˙−, thereby demonstrating the photoinduced electron transfer from SWCNT to the C60 unit in the 1-SWCNT assembly.

Efficient photocurrent generation by SnO2 electrode modified electrophoretically with composite clusters of porphyrin-modified silica microparticle and fullerene

A silica microparticle has been successfully employed as a nanoscaffold to self-organize porphyrin and C60 molecules on a nanostructured SnO2 electrode which exhibits efficient photocurrent generation.