Digital photoswitching of fluorescence based on the photochromism of diarylethene derivatives at a single-molecule level

Photochromic reactions of diarylethene derivatives were detected at a single-molecule level by using a fluorescence technique. Fluorescent photoswitching molecules in which photochromic diarylethene and fluorescent bis(phenylethynyl)anthracene units are linked through an adamantyl spacer were synthesized, and switching of fluorescence upon irradiation with UV and visible light was followed in solution as well as on polymer films at the single-molecule level. Although in solution the fluorescence intensity gradually changed upon irradiation with UV and visible light, digital on/off switching between two discrete states was observed at the single-molecule level. The "on"- and "off"-times were dependent on the power of UV and visible light. When the power of UV and visible light was increased, the average on- and off-times became short in proportion to the reciprocal power of the light. The response-times were found to show distribution. The distribution of the on- and off-times is considered to reflect the difference in the micro-environment as well as conformation of the molecules.     

Highly efficient and photostable photosensitizer based on BODIPY chromophore

Photosensitizers are reagents that produce reactive oxygen species upon light illumination and are commonly used to study oxidative stress or for photodynamic therapy. There are many available photosensitizers, but most have limitations, such as low photostability, structural instability, or a limited usable range of solvent conditions. Here, we describe a novel photosensitizer scaffold (2I-BDP) based on the unique characteristics of the BODIPY chromophore (i.e., high extinction coefficient, high photostability, and insensitivity to solvent environment). 2I-BDP shows stronger near-infrared singlet oxygen luminescence emission and higher photostability than the well-known photosensitizer, Rose Bengal. Unlike other photosensitizers, this scaffold is widely applicable under various conditions, including lipophilic and aqueous environments. HeLa cells loaded with 2I-BDP could be photosensitized by light illumination, demonstrating that 2I-BDP is potentially useful as a reagent for cell photosensitization, oxidative stress studies, or PDT.     

Studies on ferrocene derivatives. Part XVI: steric effects on the ligand exchange reactions of alkylferrocenes

Ligand exchange reactions of alkylferrocenes with substituted benzenes were carried out. The steric effects of substituents on the reaction were almost equal irrespective of the site of the substituents, either on the cyclopentadienyl – or the benzene ring. For benzene ring substituents, the effect on the symmetrically substituted benzenes was greater than that on the unsymmetrically substituted benzenes.     

Structure of cinerarin, a tetra-acylated anthocyanin isolated from the blue garden cineraria,

Structure of cinerarin is determined to be 3-0-(6-0-malonyl-β-D-glucopyranosyl)-7-0-(6-0-(4-0-(6-0-caffeyl-β-D-glucopyranosyl)caffeyl)-β-D-glucopyranosyl)-3′-0-(6-0-caffeyl-β-D-glucopyranosyl)delphinidin.     

Effect of atmospheric pressure on the phase transitions of α,α-trehalose dihydrate DTA study of the dehydration behavior in open systems

The phase transitions of α,α-trehalose dihydrate (T _h) were investigated by either differential thermal analysis (DTA) with an in-house apparatus of variable-pressure type equipped with an open sample holder or commercially available TG (thermal gravimetry)-DTA apparatus for comparison under the same experimental conditions as to the heating rate (2°C min⁻¹), the type of pan (open), and the particle size of T _h (63 μm). The former DTA measurements were carried out under five different total pressures, 101, 75, 61, 48 and 35 kPa, which provided quite helpful information necessary for confirmative assignments of the endothermic peaks due to either melting or dehydration of T _h. The usage of largely different amount of T _h, 126 and 14 mg for the DTA and TG-DTA measurements respectively, led to their different DTA traces, showing that there were largely different extents of the influence by the measured sample surface exposed to the surrounding atmosphere on its dehydration behavior. In addition the high thermal sensitivity achieved with such mass of T _h gave rise to an interesting discovery of an unidentified thermal event at 92°C prior to either melting or dehydration of T _h.     

Effect of heat treatment on magnetic MgFe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles

MgFe₂O₄ (Mg-ferrite) nanoparticles encapsulated in amorphous SiO₂ were prepared by the wet chemical method. The particle sizes were estimated, based on the X-ray diffraction peaks, to be between 3 and 8 nm, depending on the annealing temperature. The particle size increased as the annealing temperature increased. From the magnetization measurements, the blocking temperature, T _b, was found to be between 30 and 60 K. The magnetization values varied with the annealing or quenching conditions. To clarify the process of crystal growth, thermogravimetric and differential thermal analysis (TG-DTA) measurements were performed and the results were compared with the X-ray diffraction patterns.     

Ion chemistry of 1H-1,2,3-triazole

A combination of experimental methods, photoelectron-imaging spectroscopy, flowing afterglow-photoelectron spectroscopy and the flowing afterglow-selected ion flow tube technique, and electronic structure calculations at the B3LYP/6-311++G(d,p) level of density functional theory (DFT) have been employed to study the mechanism of the reaction of the hydroxide ion (HO-) with 1H-1,2,3-triazole. Four different product ion species have been identified experimentally, and the DFT calculations suggest that deprotonation by HO- at all sites of the triazole takes place to yield these products. Deprotonation of 1H-1,2,3-triazole at the N1-H site gives the major product ion, the 1,2,3-triazolide ion. The 335 nm photoelectron-imaging spectrum of the ion has been measured. The electron affinity (EA) of the 1,2,3-triazolyl radical has been determined to be 3.447 +/- 0.004 eV. This EA and the gas-phase acidity of 2H-1,2,3-triazole are combined in a negative ion thermochemical cycle to determine the N-H bond dissociation energy of 2H-1,2,3-triazole to be 112.2 +/- 0.6 kcal mol-1. The 363.8 nm photoelectron spectroscopic measurements have identified the other three product ions. Deprotonation of 1H-1,2,3-triazole at the C5 position initiates fragmentation of the ring structure to yield a minor product, the ketenimine anion. Another minor product, the iminodiazomethyl anion, is generated by deprotonation of 1H-1,2,3-triazole at the C4 position, followed by N1-N2 bond fission. Formation of the other minor product, the 2H-1,2,3-triazol-4-ide ion, can be rationalized by initial deprotonation of 1H-1,2,3-triazole at the N1-H site and subsequent proton exchanges within the ion-molecule complex. The EA of the 2H-1,2,3-triazol-4-yl radical is 1.865 +/- 0.004 eV.     

Reaction of 6‐aryl‐ or styryl‐4‐methylsulfanyl‐2‐oxo‐2H‐pyrans with active methylene compounds and fluorescence properties of the products

New 2‐pyrone derivatives, dialkyl 3‐cyano‐6‐phenyl‐2‐oxo‐2H‐pyran‐4‐ylmalonates and alkyl 3‐cyano‐6‐phenyl‐2‐oxo‐2H‐pyran‐4‐ylacetates, which were easily prepared by the reaction of 6‐aryl‐4‐methyl‐sulfanyl‐2‐oxo‐2H‐pyran‐3‐carbonitriles with active methylene compounds in the presence of potassium carbonate, show fluorescence emission radiation. The light‐emitting region of dimethyl 3‐cyano‐6‐(4‐N,N‐dimethylamino)styryl‐2‐oxo‐2H‐pyran‐4‐ylmalonate ( 7h ) was 620 nm in dichloromethane, making this compound a typical red fluorescent compound. Methyl 8‐hydroxy‐6‐methyl‐1‐oxo‐3‐phenyl‐1H‐pyrano‐[3,4‐c]pyridine‐5‐carboxylate deriv‐atives also showed fluorescence in the solid state. This is the first example of fluorescence in fused 2‐pyrone derivatives.     

Superconductivity induced by co-doping in quaternary fluoroarsenide CaFeAsF

A new quaternary fluoroarsenide CaFeAsF with the tetragonal ZrCuSiAs-type structure composed of alternate stacking of (FeAs)delta- and (CaF)delta+ layers was synthesized. CaFeAsF is a poor metal and shows the anomaly at approximately 120 K in temperature dependence of electrical conductivity. The electron doping by the partial replacement of the iron with cobalt suppresses the anomaly and induces the bulk superconductivity (optimal Tc = 22 K for CaFe0.9Co0.1AsF), analogous to recently discovered FeAs-based superconductors. The present results suggest that CaFeAsF is a promising candidate as a parent compound for high Tc superconductors.