Integration of porous coordination polymers and gold nanorods into core-shell mesoscopic composites toward light-induced molecular release.

Besides conventional approaches for regulating in-coming molecules for gas storage, separation, or molecular sensing, the control of molecular release from the pores is a prerequisite for extending the range of their application, such as drug delivery. Herein, we report the fabrication of a new porous coordination polymer (PCP)-based composite consisting of a gold nanorod (GNR) used as an optical switch and PCP crystals for controlled molecular release using light irradiation as an external trigger. The delicate core-shell structures of this new platform, composed of an individual GNR core and an aluminum-based PCP shell, were achieved by the selective deposition of an aluminum precursor onto the surface of GNR followed by the replication of the precursor into aluminum-based PCPs. The mesoscopic structure was characterized by electron microscopy, energy dispersive X-ray elemental mapping, and sorption experiments. Combination at the nanoscale of the high storage capacity of PCPs with the photothermal properties of GNRs resulted in the implementation of unique motion-induced molecular release, triggered by the highly efficient conversion of optical energy into heat that occurs when the GNRs are irradiated into their plasmon band. Temporal control of the molecular release was demonstrated with anthracene as a guest molecule and fluorescent probe by means of fluorescence spectroscopy.

Anionic complexes of MWCNT with supergiant cyanobacterial polyanions.

Multi-walled carbon nanotubes (MWCNTs) were well dispersed in an aqueous solution of the cyanobacterial polysaccharide, sacran, with an ultra-high molecular weight >10 million g/mol. MWCNTs powder was put into aqueous solutions of various polysaccharides including sacran and was dispersed under sonication. As a result of the turbidity measurement of the supernatant, it was found that sacran showed the highest MWCNT-dispersion efficiency of all the polysaccharides used here. Cryogenic transmission electron microscopic (Cryo-TEM) studies directly demonstrated the existence of MWCNTs in the supernatant, and high-resolution TEM observation revealed that MWCNTs covered by sacran chains made their efficient dispersion in water. Raman spectroscopy demonstrated the existence of MWCNT in dried sample from supernatant and the interaction between MWCNT and sacran. The ζ-potential measurement of the dispersion indicated the negative surface charges of the sacran/MWCNT complexes. Then the MWCNT complexes were able to fabricate by ionic interaction; electrophoresis of the anionic complex formed the sacran/MWCNT gels on the anode while the droplet of sacran/MWCNT dispersion formed gel beads in the presence of the lanthanoid cations.

Guest-to-host transmission of structural changes for stimuli-responsive adsorption property.

We show that structural changes of a guest molecule can trigger structural transformations of a crystalline host framework. Azobenzene was introduced into a flexible porous coordination polymer (PCP), and cis/trans isomerizations of the guest azobenzene by light or heat successfully induced structural transformations of the host PCP in a reversible fashion. This guest-to-host structural transmission resulted in drastic changes in the gas adsorption property of the host-guest composite, displaying a new strategy for creating stimuli-responsive porous materials.

Highly photoconducting π-stacked polymer accommodated in coordination nanochannels.

We report on the formation of single poly(N-vinylcarbazole) (PVCz) chains in one-dimensional channels of [La(1,3,5-benzenetrisbenzoate)](n), where the side carbazolyl groups of the confined PVCz are effectively π-stacked. This ideal conformation of PVCz chains in the coordination nanochannels contributed to a drastic increase in hole mobility, which was 5 orders of magnitude higher than that in the bulk state. It is also noteworthy that PVCz isolated from the nanchannels still had a high hole mobility.

Photodynamic and photothermal effects of semiconducting and metallic-enriched single-walled carbon nanotubes.

Semiconducting and metallic single-walled carbon nanotubes (s-SWNTs and m-SWNTs) were enriched by agarose gel chromatography and their photothermal and photodynamic effects were compared in H(2)O. Under near-infrared laser irradiation, s-SWNTs generated reactive oxygen species (ROS) more than m-SWNTs, whereas m-SWNTs produced heat more efficiently than s-SWNTs. More importantly, cancer cell killing by PDE of s-SWNTs has been disclosed for the first time.

Modular design of domain assembly in porous coordination polymer crystals via reactivity-directed crystallization process.

The mesoscale design of domain assembly is crucial for controlling the bulk properties of solids. Herein, we propose a modular design of domain assembly in porous coordination polymer crystals via exquisite control of the kinetics of the crystal formation process. Employing precursors of comparable chemical reactivity affords the preparation of homogeneous solid-solution type crystals. Employing precursors of distinct chemical reactivity affords the preparation of heterogeneous phase separated crystals. We have utilized this reactivity-directed crystallization process for the facile synthesis of mesoscale architecture which are either solid-solution or phase-separated type crystals. This approach can be also adapted to ternary phase-separated type crystals from one-pot reaction. Phase-separated type frameworks possess unique gas adsorption properties that are not observed in single-phasic compounds. The results shed light on the importance of crystal formation kinetics for control of mesoscale domains in order to create porous solids with unique cooperative functionality.

Photoinduced charge carrier dynamics of Zn-porphyrin-TiO2 electrodes: the key role of charge recombination for solar cell performance.

Time resolved absorption spectroscopy has been used to study photoinduced electron injection and charge recombination in Zn-porphyrin sensitized nanostructured TiO(2) electrodes. The electron transfer dynamics is correlated to the performance of dye sensitized solar cells based on the same electrodes. We find that the dye/semiconductor binding can be described with a heterogeneous geometry where the Zn-porphyrin molecules are attached to the TiO(2) surface with a distribution of tilt angles. The binding angle determines the porphyrin-semiconductor electron transfer distance and charge transfer occurs through space, rather than through the bridge connecting the porphyrin to the surface. For short sensitization times (1 h), there is a direct correlation between solar cell efficiency and amplitude of the kinetic component due to long-lived conduction band electrons, once variations in light harvesting (surface coverage) have been taken into account. Long sensitization time (12 h) results in decreased solar cell efficiency because of decreased efficiency of electron injection.

Gelation behavior by the lanthanoid adsorption of the cyanobacterial extracellular polysaccharide.

The self-organization behavior of an extracellular polysaccharide (sacran) extracted from the cyanobacterium Aphanothece sacrum in response to lanthanoid ion adsorption was investigated. Consequently, cryogenic TEM images revealed that sacran could be cross-linked by Nd(3+) trivalent ions and formed a fibrous nanostructural network containing water. Furthermore, sacran adsorbed trivalent metal ions at a 3:1 ratio, which was the theoretical ionic adsorption and showed more efficient adsorption than alginate based on electric conductivity titration. The critical gelation concentrations, Cg, where sacran formed tough gels upon metal ion binding were estimated. The Cg for trivalent metal ions was lower than that for divalent ions, and the Cg for lanthanoid ions was particularly low at 10(-3) to 10(-4) M, changing every four elemental numbers. The extracellular matrix of Aphanothece sacrum, sacran, may adsorb metal ions to create fibrous nanostructures that reinforce the jelly matrix.

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.

Chemical shift of electron energy-loss near-edge structure on the nitrogen K-edge and titanium L3-edge at TiN/Ti interface.

We investigated the chemical shift of the electron energy-loss near-edge structure (ELNES) for the nitrogen K-edge and titanium L3-edge measured from the interface region between a titanium nitride layer and a titanium layer. Both the titanium nitride and titanium layers were prepared by a sputtering method. Elemental analysis for nitride and titanium in the vicinity of the interface region was performed using a standard technique in electron energy-loss spectroscopy. It was demonstrated that both the ELNES of nitrogen K-edge and titanium L3-edge presented the chemical shift, more or less, depending on the composition of TiNx. The experimental findings were interpreted using a first-principles band structure calculation. The chemical shifts of nitrogen K-edge and titanium L3-edge can be used as fingerprinting for readily distinguishing the composition of TiNx.

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.

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.

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.

Atomic resolution ADF-STEM imaging of organic molecular crystal of halogenated copper phthalocyanine.

Annular dark-field (ADF) scanning transmission electron microscopy (STEM) measurements are demonstrated for the first time to be applicable for acquiring Z-contrast images of organic molecules at atomic resolution. High-angle ADF imaging by STEM is a new technique that provides incoherent high-resolution Z-contrast images for organic molecules. In the present study, low-angle ADF-STEM is successfully employed to image the molecular crystal structure of hexadecachloro-Cu-phthalocyanine (Cl16-CuPc), an organic molecule. The structures of CuPc derivatives (polyhalogenated CuPc with Br and Cl) are determined quantitatively using the same technique to determine the occupancy of halogens at each chemical site. By comparing the image contrasts of atomic columns, the occupancy of Br is found to be ca. 56% at the inner position, slightly higher than that for random substitution and in good agreement with previous TEM results.

Energy-loss near-edge structure (ELNES) and first-principles calculation of electronic structure of nickel silicide systems.

The electronic structures of nanometre-sized nickel silicide systems, Ni(2)Si and NiSi, have been studied by energy-loss near-edge structure (ELNES) and first-principles band structure calculations. Experimental ELNES of Ni L(3)- and Si L(2,3)-edges could be explained well using theoretical spectra calculated for the ground state without the core hole, suggesting metallic properties for both silicides. It was shown that a slight difference in ELNES spectra of Ni(2)Si and NiSi comes from the coupling among the Ni d and Si p, d states in the unoccupied bands. The density of states and the contour plots of all the valence electron densities for Ni(2)Si, NiSi together with NiSi(2) show that Ni(2)Si has the bond with the strongest covalent character between Ni and Si atoms and the most transition metal-like character of the Ni 3d band among the three silicides.

Formation of self-assembled glycolipid nanotubes with bilayer sheets.

Rolled-up morphology of bilayer sheets in a self-assembled glycolipid nanotube (LNT) in water was carefully examined by using a cryogenic transmission electron microscope (cryo-TEM) with a rapid-freezing specimen-preparation technique. The LNTs were obtained under a series of self-assembly conditions: boiling of an aqueous dispersion of glycolipid N-(11-cis-octadecenoyl)-beta-D-glucopyranosylamine, subsequent gradual cooling, and incubation at room temperature for several days. Cryo-TEM images revealed that the LNT walls consist of a multilayer structure with interlayer distance of about 4.7 nm. These layers correspond to constituent lipid bilayers. From the result of precise cryo-TEM observations and analyses, we confirmed the rolled-up morphology of the lipid bilayer sheets in a complete self-assembled glycolipid nanotube.

Dye-sensitized solar cells based on a single-crystalline TiO2 nanorod film.

Highly crystalline TiO2 nanorods with lengths of 100-300 nm and diameters of 20-30 nm have been synthesized by a hydrothermal process in a cetyltrimethylammonium bromide surfactant solution. The microstructure measured by X-ray diffraction and high-resolution transmission electron microscopy was a pure highly crystalline anatase phase with a long nanorod shape. The addition of a triblock copolymer poly(ethylene oxide)100-poly(propylene oxide) 65-poly(ethylene oxide)100 (F127) decreased the length of the nanorods and kept the rod shape of the particles even after sintering at high temperatures. The rod shape kept under high calcination temperatures contributed to the achievement of the high conversion efficiency of light-to-electricity as discussed in the paper. A high conversion efficiency of light-to-electricity of 7.29% was obtained with the TiO2 single-crystalline anatase nanorod cell.

Determination of parameters of electron transport in dye-sensitized solar cells using electrochemical impedance spectroscopy.

The same equation was derived from two different impedance models based on the quite different physical descriptions proposed by Kern et al.(1) and by Bisquert.(2,3) Reliable values of the parameters relating to electron transport in dye-sensitized solar cells can be determined from measured spectra by electrochemical impedance spectroscopy when careful analysis of the measured spectra is done based on the classification and clarification of the same impedance equation consequent from the two models. The requisites for making highly efficient dye-sensitized solar cells were proposed.

A photoelectrochemical device with a nanostructured SnO2 electrode modified with composite clusters of porphyrin-modified silica nanoparticle and fullerene.

A silica nanoparticle has been successfully employed as a nanoscaffold to self-organize porphyrin and C60 molecules on a nanostructured SnO2 electrode. The quenching of the porphyrin excited singlet state on the silica nanoparticle is suppressed significantly, showing that silica nanoparticles are promising scaffolds for organizing photoactive molecules three-dimensionally in nanometer scale. Marked enhancement of the photocurrent generation was achieved in the present system compared with the reference system, where a gold core was employed as a scaffold of porphyrins instead of a silica nanoparticle. The rather small incident photon-to-current efficiency relative to a similar photoelectrochemical device using a silica microparticle may result from poor electron and hole mobility in the composite film due to poor connection between the composite clusters of a porphyrin-modified silica nanoparticle and C60 in micrometer scale.