Institute of Advanced Energy, Kyoto University

The synthesis of a carbon nanobelt, comprising a closed loop of fully fused edge-sharing benzene rings, has been an elusive goal in organic chemistry for more than 60 years. Here we report the synthesis of one such compound through iterative Wittig reactions followed by a nickel-mediated aryl-aryl coupling reaction. The cylindrical shape of its belt structure was confirmed by x-ray crystallography, and its fundamental optoelectronic properties were elucidated by ultraviolet-visible absorption, fluorescence, and Raman spectroscopic studies, as well as theoretical calculations. This molecule could potentially serve as a seed for the preparation of structurally well-defined carbon nanotubes.

Highly efficient dye-sensitized solar cells were produced using single-crystalline nanotubes as a thin-film semiconductor because of the very high electron transfer through single-crystalline nanotubes when compared to that through nanoporous films composed of nanoparticles. The dye-sensitized solar cells with single-crystalline nanotubes showed more than double the short-circuit current density than those made of titania nanoparticles Degussa P-25 in the thin-film thickness region. Titania nanotubes were synthesized using molecular assemblies composed of surfactant molecules, i.e. , laurylamine hydrochloride, and titanium alkoxide, i.e. , tetraisopropylorthotitanate modified with acetylacetone, as a template. They have outer and inner diameters of about 10 and 5 nm, respectively, a length in the range from 30 nm to several hundred nanometers, and have a single-crystalline structure of anatase, as confirmed on lattice images observed by high-resolution transmission electron microscopy. The light to electricity conversion of the titania nanotube cells was around 5%. They also showed the highest photocatalytic activity when compared to the commercially available nanocrystalline titania. © 2003 The Electrochemical Society. All rights reserved.

Abstract Titania nanotubes with high photo-catalytic activity were synthesized in laurylamine hydrochloride / tetraisopropyl orthotitanate modified with acetylacetone system. Formation of nanotubes was confirmed by transmission electron microscope images. These titania nanotubes had crystal structure of anatase and showed high photo-catalytic activity, i.e., the activity is about three times higher than Degussa-P-25 and higher than ST-01.

-connected benzene rings. Characteristic fluorescence of a heterocatenane associated with fast energy transfer between two rings was observed, and the topological chirality of the all-benzene knot was confirmed by enantiomer separation and circular dichroism spectroscopy. The seemingly rigid all-benzene knot has rapid vortex-like motion in solution even at -95°C, resulting in averaged nuclear magnetic resonance signals for all hydrogen atoms. This interesting dynamic behavior of the knot was theoretically predicted and could stimulate deeper understanding and applications of these previously untapped classes of topological molecular nanocarbons.

We studied multiexciton dynamics in monolayer ${\mathrm{WSe}}_{2}$ using nonlinear photoluminescence (PL) spectroscopy and Monte Carlo simulations. We observed strong nonlinear saturation behavior of exciton PL with increasing excitation power density and long-distance exciton diffusion, reaching several micrometers. We demonstrated that the diffusion-assisted exciton-exciton annihilation (EEA) model accounts for the observed nonlinear PL behavior. The long-distance exciton diffusion and subsequent efficient EEA process determined the unusual multiexciton dynamics in atomically thin layered transition metal dichalcogenides.

SiC nanowires (NWs) reinforce SiC matrix composites with high efficiency. With the incorporation of ∼ 6 vol.-% randomly oriented single-crystal SiC NWs in the matrices, the fracture toughnesses and flexural strengths of the composites doubled. The composites (see Figure) were fabricated in situ by a new process based on chemical vapor infiltration. Reinforcement efficiency of the NW is affected by the amount of C deposited on the NWs as the NW/matrix interfacial layer.

Shell is of great significance to the enhancement in the photoluminescence quantum yield (PLQY) and stability of core–shell-type quantum dots (QDs). InP/ZnS core–shell QDs without intrinsic toxicity have shown huge potential as a replacement for the widely used cadmium-containing QDs; however, it is still challenging to control the growth of InP-based core–shell QDs due to the lattice mismatch between the InP core and ZnS shell. Here, we report on the synthesis of ∼15-nm-size InP/ZnSe/ZnS QDs with a thick ZnS outer shell by a layer-by-layer shell growth strategy. The ZnS shell was prepared by a circularly gradient temperature rise and long reaction procedure in each step, which not only ensures relatively low precursor concentration preventing the anisotropic growth of QDs but also allows the low-reactivity source to be decomposed sufficiently to achieve layer-by-layer growth of a thick ZnS shell. The resulting QDs show the highest PLQY of 73%, narrow emission line width of up to 40 nm, wide spectrum tunability, and excellent stability. Furthermore, the thick ZnS shell also effectively suppresses nonradiative Förster resonant energy transfer and Auger recombination within QDs. As a result, these enable our quantum dot light-emitting diodes (QLEDs) to achieve a record external quantum efficiency of 6.6% in heavy-metal-free red QLEDs.

The synthesis and X-ray crystal structure of the first member of the carbon nanobelt family is reported. [12]Carbon nanobelt ([12]CNB) was originally obtained from a nickel-mediated reductive coupling reaction of a dodecabrominated macrocyclic precursor, albeit only in 1% yield. The present article reports on the development of this synthetic strategy and its extension to the preparation of the [16] and [24]CNB analogues. In particular, our extensive investigations on the final belt-forming, nickel-mediated reaction led to the development of a new ligand system that provides [12]CNB in up to 7% yield, contributing to the commercialization of [12]CNB. The belt structures of [12], [16], and [24]CNB were characterized by NMR, UV-vis, and Raman spectroscopy as well as mass spectrometry and X-ray crystallography. The fluorescence of the CNBs in solution displayed a remarkable dependence on the ring size, ranging from a broad red emission ([12]CNB) to a narrow-band blue emission ([24]CNB), while both features are observed for [16]CNB.

We report the construction of an artificial enzyme cascade based on the xylose metabolic pathway. Two enzymes, xylose reductase and xylitol dehydrogenase, were assembled at specific locations on DNA origami by using DNA-binding protein adaptors with systematic variations in the interenzyme distances and defined numbers of enzyme molecules. The reaction system, which localized the two enzymes in close proximity to facilitate transport of reaction intermediates, resulted in significantly higher yields of the conversion of xylose into xylulose through the intermediate xylitol with recycling of the cofactor NADH. Analysis of the initial reaction rate, regenerated amount of NADH, and simulation of the intermediates' diffusion indicated that the intermediates diffused to the second enzyme by Brownian motion. The efficiency of the cascade reaction with the bimolecular transport of xylitol and NAD(+) likely depends more on the interenzyme distance than that of the cascade reaction with unimolecular transport between two enzymes.

The emission spectra from the solid–liquid interface irradiated by a pulsed laser were studied. The solid target used in this study was graphite and boron nitride, and the liquid in which the target was immersed was water, benzene, n-hexane, and carbon tetrachloride. The results showed strong continuous spectrum immediately after a pulse shot, whereas after ≈100 ns later from the irradiation it was greatly reduced, and instead, the emission from small molecules dominated the spectra. The line spectra of small molecules observed in the later time range indicate the chemical reaction between the ablated species and the species originated from the liquid molecules. The intensity of the continuous spectrum was very prominent compared to what has been observed for solid–gas interfaces. This is due to rapid electron ion recombination or bremsstrahlung due to highly confined interface plasma.

Point the finger: Zinc-finger proteins are convenient and site-selective adaptors for targeting specific locations within DNA-origami structures. Orthogonal targeting of the specific locations in the structures was demonstrated by using two adaptors, and the application of Escherichia coli lysate that contained the adaptor-fused proteins successfully afforded the expected protein–DNA assembly.

Photoluminescence phenomena normally obey Stokes' law of luminescence according to which the emitted photon energy is typically lower than its excitation counterparts. Here we show that carbon nanotubes break this rule under one-photon excitation conditions. We found that the carbon nanotubes exhibit efficient near-infrared photoluminescence upon photoexcitation even at an energy lying >100-200 meV below that of the emission at room temperature. This apparently anomalous phenomenon is attributed to efficient one-phonon-assisted up-conversion processes resulting from unique excited-state dynamics emerging in an individual carbon nanotube with accidentally or intentionally embedded localized states. These findings may open new doors for energy harvesting, optoelectronics and deep-tissue photoluminescence imaging in the near-infrared optical range.

The layered structures of graphite and related nanographene molecules play key roles in their physical and electronic functions. However, the stacking modes of negatively curved nanographenes remain unclear, owing to the lack of suitable nanographene molecules. Herein, we report the synthesis and one-dimensional supramolecular self-assembly of negatively curved nanographenes without any assembly-assisting substituents. This curved nanographene self-assembles in various organic solvents and acts as an efficient gelator. The formation of nanofibers was confirmed by microscopic measurements, and an unprecedented double-helix assembly by continuous π–π stacking was uncovered by three-dimensional electron crystallography. This work not only reports the discovery of an all-sp 2 -carbon supramolecular π-organogelator with negative curvature but also demonstrates the power of three-dimensional electron crystallography for the structural determination of submicrometer-sized molecular alignment.

Nano-carbon materials (carbon nanotubes, graphene, and graphene oxide) have potential application for photovoltaics because of their excellent optical and electronic properties. Here, we demonstrate that a single-walled carbon nanotubes/graphene oxide buffer layer greatly improves the photovoltaic performance of organo-lead iodide perovskite solar cells. The carbon nanotubes/graphene oxide buffer layer works as an efficient hole transport/electron blocking layer. The photovoltaic conversion efficiency of 13.3% was achieved in the organo-lead iodide perovskite solar cell due to the complementary properties of carbon nanotubes and graphene oxide. Furthermore, the great improvement of photovoltaic performance stability in the perovskite solar cells using carbon nanotubes/graphene oxide/polymethyl methacrylate was demonstrated in comparison with that using a typical organic hole transport layer of 2,2',7,7'-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9'-spirobifluorene.

The formation processes of the silica nanotubes by a surfactant-assisted templating mechanism were elucidated in a laurylamine hydrochloride (LAHC)/tetraethoxysilane (TEOS) system by measuring the evolution of the shape and size of surfactant/silicate molecular assemblies with small-angle X-ray scattering, together with TEM, SEM, nitrogen adsorption isotherm, and 29 Si NMR. The formation processes in dilute LAHC solution at pH 4.5 are elucidated as follows. Partially hydrolyzed TEOS penetrates into finely divided bilayerlike surfactant assemblies and converts the assemblies to globular aggregates. Then, the polymerization of the hydrolyzed TEOS proceeds on the surface of the aggregates, converting the aggregates to cylindrical form due to the geometric matching between the occupied area of a surfactant molecule and that of four SiO 2 molecules at the surface of the cylinder. Then, the cylinders connect with each other at the cylinders spherical end cap because of the relative instability at the end caps due to the lack of geometric matching. Some long cylinders combine and generate bundles composed of a range of several to dozens of fine silica nanotubes. The long bundles make a network structure by cross-linking, and the solution becomes a gel. The important factors controlling the microstructure formation are (1) geometric matching of the occupied area between the silicate molecules and the surfactants at the interface and (2) the packing parameter of the silicate/surfactant assemblies. The elucidated formation processes were confirmed by the formation of long length bundles of nanosize tubules with the aid of trimethylsilylation.

The morphological change of p-type porous silicon during annealing has been investigated. The x-ray diffraction (XRD) pattern was composed of a sharp Bragg reflection peak and a diffuse scattering. The diffuse scattering is not related to the presence of the amorphous phase. The shape of the XRD pattern started to change at an annealing temperature as low as 400 °C, and the 2θ angle of the sharp peak varied at a temperature as low as 350 °C. These changes at low temperatures seem to be closely related to the desorption of hydrogen and the resultant change of the dangling bond density in porous silicon. The molecular orbital calculations also support the participation of dangling bonds in the structural reorganization in the surface region.

It is a central issue to elucidate the new type of molecular recognition accompanied by a global structural change of a molecule upon binding to its targets. Here we investigate the driving force for the binding of R12 (a ribonucleic acid aptamer) and P16 (a partial peptide of a prion protein) during which P16 exhibits the global structural change. We calculate changes in thermodynamic quantities upon the R12-P16 binding using a statistical-mechanical approach combined with molecular models for water which is currently best suited to studies on hydration of biomolecules. The binding is driven by a water-entropy gain originating primarily from an increase in the total volume available to the translational displacement of water molecules in the system. The energy decrease due to the gain of R12-P16 attractive (van der Waals and electrostatic) interactions is almost canceled out by the energy increase related to the loss of R12-water and P16-water attractive interactions. We can explain the general experimental result that stacking of flat moieties, hydrogen bonding and molecular-shape and electrostatic complementarities are frequently observed in the complexes. It is argued that the water-entropy gain is largely influenced by the geometric characteristics (overall shapes, sizes and detailed polyatomic structures) of the biomolecules.

Nanosize bundles of huge lengths of silica-nanotubes were synthesized by a surfactant-assisted templating mechanism in a laurylamine hydrochloride/tetraethoxysilane system with the aid of trimethylsilylation treatment. The transmission electron microscopy images confirmed the formation of the bundles of silica nanotubes mentioned above. The trimethylsilylation treatment prevents the condensation reaction of silanol groups between different bundles, provides very long bundles of nanosize tubules, and also removes surfactants from the inside of silica nanotubes without calcination.

Understanding of electronic and optical features of single-walled carbon nanotubes (SWNTs) has been a central issue in science and nanotechnology of carbon nanotubes. We describe the detection of both the positive trion (positively charged exciton) and negative trion (negatively charged exciton) as a three-particle bound state in the SWNTs at room temperature by an in situ photoluminescence spectroelectrochemistry method for an isolated SWNT film cast on an ITO electrode. The electrochemical hole and electron dopings enable us to detect such trions on the SWNTs. The large energy difference between the singlet bright exciton and the negative and positive trions showing a tube diameter dependence is determined by both the exchange splitting energy and the trion binding energy. In contrast to conventional compound semiconductors, on the SWNTs, the negative trion has almost the same binding energy to the positive trion, which is attributed to nearly identical effective masses of the holes and electrons.

Jones, and broad spectral response in the wavelength range of 300-800 nm. More importantly, the GeS photodetector has high polarization sensitivity to incident linearly polarized light, which provides another degree of freedom for photodetectors. Tremendously enhanced photoresponsivity is observed with a temperature increase, and high responsivity is achievable at least up to 423 K. The establishment of larger photoinduced reduction of the Schottky barrier height will be significant for the investigation of the photoresponse mechanism of 2D layered material-based photodetectors. These attributes of high photocurrent generation in a wide temperature range, broad spectral response, and polarization sensitivity coupled with environmental stability indicate that the proposed GeS photodetector is very suitable for optoelectronic applications.