Capturing one-dimensional precursors of a photoinduced transformation in a material

Achieving control of photoinduced phase transitions requires understanding how materials work during transformation induced by a laser pulse. Here we investigate the precursors of a photoinduced phase transition in the highly cooperative charge-transfer molecular crystal tetrathiafulvalene-p-chloranil and provide key insights. The photogeneration of one-dimensional nanoscale clusters was detected by time-resolved diffuse x-ray scattering with 50-ps time resolution. Such clustering of structurally relaxed electronic excitations is expected to be a common process in many materials presenting photoinduced transformations.     

Boundaries between square-shaped,nitrogen-adsorbed islands on Cu(001): Two relief mechanisms of the stress induced by atomic adsorbates

We have performed a scanning tunneling microscopy study on a grid-like mesoscopic pattern formed by nitrogen adsorption on a Cu(001) surface. Two types of boundaries are present between square-shaped N-adsorbed islands: a fine straight line of monoatomic width (“monoatomic line”) and a bare Cu(001) belt of several atoms wide (“multiatomic belt”). The boundary type depends on whether c(2 × 2) protrusions in neighboring islands are aligned in-phase or out-of-phase across the boundary. Considering that an adsorbed N atom prefers to be coordinated by four Cu atoms on a plane and that the topmost Cu layer is expanded by 2–3% by N adsorption, we propose the missing-Cu-atom model for a monoatomic line where a single Cu row is ejected by a compressive stress exerted from neighboring N-islands. The reconstruction maintains the planar 4-fold coordination of Cu atoms to an N atom in the case of in-phase alignment, and relieves the N-induced compressive stress very efficiently. Whereas, the Cu row ejection would destroy the stable local structure in the out-of-phase case. The N-induced compressive stress is relieved in the other mechanism where it is compensated with a tensile stress in a bare Cu(001) region. The region is imaged as a multiatomic belt. The above models for a monoatomic line and a multiatomic belt explain well various features observed in the grid pattern. Moreover, the missing-Cu-atom model rationalizes the attractive interaction between N-islands which was difficult to understand in a traditional, elasticity-based view on the self-organization.     

Photochemical fine-tuning of luminescent color of cadmium selenide nanoparticles: fabricating a single-source multicolor luminophore

Size-selective photoetching was applied to silica-coated cadmium selenide (SiO2/CdSe) nanoparticles to precisely control their photoluminescence properties. The absorption spectra of CdSe was blue-shifted by irradiation of monochromatic light, and finally, the absorption onset agreed with the wavelength of irradiation light, indicating that CdSe particles were photoetched to smaller ones until the irradiated photons were not absorbed by the photoetched particles and that the SiO2 shell layer surrounding the CdSe core prevented coalescence between the photoetched particles. Although as-prepared SiO2/CdSe did not exhibit photoluminescence, the application of size-selective photoetching to SiO2/CdSe resulted in the development of the band gap emission, with the degree being enhanced with progress of the photoetching. The peak wavelength of photoluminescence decreased with a decrease in the wavelength used for the photoetching, so that the luminescence color could be tuned between red and blue. Partial photoetching of SiO2/CdSe nanoparticle films produced intense band gap emission of CdSe at the photoetched area, while the remainder of the SiO2/CdSe films did not exhibit detectable photoluminescence, resulting in the formation of a clear photoluminescence image under UV irradiation. This technique makes it possible to produce a multicolored photoluminescence image by irradiation with monochromatic lights having various wavelengths using a single source material.     

A Water-Gated Organic Thin-Film Transistor for Glyphosate Detection: A Comparative Study with Fluorescence Sensing

This work reports the design of a highly sensitive solid-state sensor device based on a water-gated organic thin-film transistor (WG-OTFT) for the selective detection of herbicide glyphosate (GlyP) in water. A competitive assay among carboxylate-functionalized polythiophene, Cu²⁺, and GlyP was employed as a sensing mechanism. Molecular recognition phenomena and electrical double layer (EDL) (at the polymer/water interface) originated from the field-effect worked cooperatively to amplify the sensitivity for GlyP. The limit of detection of WG-OTFT (0.26 ppm) was lower than that of a fluorescence sensor chip (0.95 ppm) which is the conventional sensing method. In contrast to the previously reported insulated molecular wires to block interchain interactions, molecular aggregates under the field-effect has shown to be effective for amplification of sensitivity through “intra”- and “inter”-molecular wire effects. The opposite strategy in this study could pave the way for fully utilizing the sensing properties of polymer-based solid-state sensor devices.     

High-efficiency tris(8-hydroxyquinoline)aluminum (Alq3) complexes for organic white-light-emitting diodes and solid-state lighting

Combinations of electron-withdrawing and -donating substituents on the 8-hydroxyquinoline ligand of the tris(8-hydroxyquinoline)aluminum (Alq(3)) complexes allow for control of the HOMO and LUMO energies and the HOMO-LUMO gap responsible for emission from the complexes. Here, we present a systematic study on tuning the emission and electroluminescence (EL) from Alq(3) complexes from the green to blue region. In this study, we explored the combination of electron-donating substituents on C4 and C6. Compounds 1-6 displayed the emission tuning between 478 and 526 nm, and fluorescence quantum yield between 0.15 and 0.57. The compounds 2-6 were used as emitters and hosts in organic light-emitting diodes (OLEDs). The highest OLED external quantum efficiency (EQE) observed was 4.6%, which is among the highest observed for Alq(3) complexes. Also, the compounds 3-5 were used as hosts for red phosphorescent dopants to obtain white light-emitting diodes (WOLED). The WOLEDs displayed high efficiency (EQE up to 19%) and high white color purity (color rendering index (CRI≈85).     

Total synthesis of spiruchostatin B aided by an automated synthesizer

The total synthesis of a natural product HDAC inhibitor, spiruchostatin B, was successfully achieved. A 5-step synthesis that included an asymmetric aldol reaction was carried out in an automated synthesizer to provide an (E)-(S)-3-hydroxy-7-thio-4-heptenoic acid segment that is the crucial structure of cysteine-containing, depsipeptidic natural products such as spiruchostatins, FK228, FR901375, and largazole for their inhibitory activity against HDACs.     

Efficient topical delivery of chlorogenic acid by an oil-in-water microemulsion to protect skin against UV-induced damage

We examined the intradermal delivery of a hydrophilic polyphenol chlorogenic acid by in vitro study using excised guinea pig dorsal skin and Yucatan micropig skin. Skin accumulation as well as the solubility of chlorogenic acid in aqueous vehicles was much greater than for other polyphenols such as quercetin and genistein. However, since enhancement of skin delivery seemed to be necessary to exhibit its protective effects against oxidative damage of skin, we examined the effects of microemulsions as vehicles. Using microemulsions consisting of 150 mM NaCl solution, isopropyl myristate, polyoxyethylene sorbitan monooleate (Tween 80) and ethanol, skin accumulation as well as solubility of chlorogenic acid further increased. Enhancement effect of an oil-in-water (o/w-type) microemulsion was greater than that of a water-in-oil (w/o-type) microemulsion possibly due to the greater increase in solubility. This finding was quite different from previous findings on relatively hydrophobic polyphenols such as quercetin and genistein. Pretreatment of guinea pig dorsal skin with chlorogenic acid containing microemulsion gel prevented erythema formation induced by UV irradiation. These findings indicate the potential use of hydrophilic chlorogenic acid with o/w-type microemulsion as a vehicle to protect skin against UV-induced oxidative damage.     

A new imaging method for gold-surface adsorbates based on anomalous reflection

A new imaging method is proposed for ultrathin films with a thickness of a few nanometers, based on the anomalous reflection (AR) of gold. In the AR effect, the reflectivity fairly decreases for blue or purple light (380 nm < λ < 480 nm) with the existence of a transparent dielectric layer at a gold surface. Thus, a thin gold film can be used as an imaging platform. Clear AR images are obtained for a microarray of protein (avidin) spots of diameter 120 μm with gaps of size 50 μm between the spots (36 spots/mm²). The resolution of the AR imaging is governed solely by the illumination spot size. AR imaging is a promising technique for high throughput analysis of biomolecular detection in a microarray format.     

Microstructural change due to isochronal annealing in severely plastic-deformed commercial purity aluminium

Microstructural changes, such as the density of grain boundary (GB) and dislocation density, due to isochronal annealing in severely plastic-deformed commercial purity aluminium up to 523 K was evaluated using electrical resistivity measurements and scanning transmission electron microscopy. Eventually, the GB density decreases from about 7.2 × 10⁶ to about 2 × 10⁶ m^?1, whilst the dislocation density decreases from an initial value of around 1.3 × 10¹⁴ m^?2 down to around 4 × 10¹³ m^?2.