Synthesis of Highly Emissive Fluorophores Based on Multiply Stacked Anthracene Arrangement

Newly designed fluorophore systems with feather-like structures were constructed by connecting bisanthracene building units via a concise reaction sequence of bromination, etherification, and desilylation. Spectroscopic characterizations revealed that all of the fluorophore systems achieved high light absorptivity and high emission efficiency by preventing closely spaced anthracene chromophores from mutual interactions to reduce concomitant energy loss by fluorescence quenching. The application of fluorophore systems for the preparation of light-harvesting dyad materials has successfully demonstrated their potential utility as versatile photofunctional tools.     

Noncovalent Modification of Cycloparaphenylene by Catenane Formation Using an Active Metal Template Strategy**

The active metal template (AMT) strategy is a powerful tool for the formation of mechanically interlocked molecules (MIMs) such as rotaxanes and catenanes, allowing the synthesis of a variety of MIMs, including π-conjugated and multicomponent macrocycles. Cycloparaphenylene (CPP) is an emerging molecule characterized by its cyclic π-conjugated structure and unique properties. Therefore, diverse modifications of CPPs are necessary for its wide application. However, most CPP modifications require early stage functionalization and the direct modification of CPPs is very limited. Herein, we report the synthesis of a catenane consisting of [9]CPP and a 2,2′-bipyridine macrocycle as a new CPP analogue that contains a reliable synthetic scaffold enabling diverse and concise post-modification. Following the AMT strategy, the [9]CPP-bipyridine catenane was successfully synthesized through Ni-mediated aryl-aryl coupling. Catalytic C−H borylation/cross-coupling and metal complexation of the bipyridine macrocycle moiety, an effective post-functionalization method, were also demonstrated with the [9]CPP-bipyridine catenane. Single-crystal X-ray structural analysis revealed that the [9]CPP-bipyridine catenane forms a tridentated complex with an Ag ion inside the CPP ring. This interaction significantly enhances the phosphorescence lifetime through improved intermolecular interactions.     

GdAlO3 perovskite

Flux‐grown gadolinium aluminate perovskite, GdAlO₃, was examined using single‐crystal 0.7 Å‐wavelength synchrotron X‐ray diffraction. In the context of other well categorized rare earth aluminate (RAlO₃) perovskite phases, the orthorhombic Pnma symmetry determined for the current compound is unsurprising. Corner‐linked AlO₆ octahedra form the structural backbone of RAlO₃ perovskites and distort to accommodate the various rare earth ions in the structural voids. For GdAlO₃, the octahedral distortion, characterized by tilting of the octahedra about the shortest R—Al—R vectors, and octahedral deformation, characterized by strain of the octahedra along those axes, are in accordance with trends in the RAlO₃ series.     

Optical properties of molecular aggregates of oxazine dyes in dispersions of clay minerals

The molecular aggregation of oxazine 1 (Ox1) and oxazine 4 (Ox4) in reduced charge montmorillonite (RCM) colloids was investigated by absorption and fluorescence spectroscopies. The aggregation was significantly influenced by the structure of dye cations. Presence of four hydrophobic ethyl groups attached to the ammonium substituents in Ox1 cation prevented formation of closely packed sandwich-type assemblies (H-aggregates). Significant effect of the layer charge was observed for Ox4/RCMs dispersions. Large amounts of the Ox4 H-aggregates were formed in the systems with RCMs of the highest layer charge and reflected in quenched fluorescence. The presence of J-aggregates was proven by absorption spectra for the systems with Ox4 and low-charge RCMs. The flocculation of the lowest charge RCM colloids led to an extensive reduction of the luminescence. The trends and effects of the dye molecular structure and RCM properties are compared with the results previously published for other types of dyes.     

Analysis of Cu segregation to oxide–metal interface of Ni‐based alloy in a metal‐dusting environment

Hard X‐ray photoelectron spectroscopy (HX‐PES) has been realized using high‐brilliance synchrotron radiation. High‐energy photon excitation enables us to probe photoelectrons with larger escape depth compared to conventional PES. This allows us to conduct, without destruction, a study of the embedded interface of materials as the oxide‐ metal interface. We apply HX‐PES to investigate for Cu segregation in the oxide–metal interface during metal‐dusting corrosion. The effective concentration of Cu in the segregation was estimated a few times higher than the bulk concentration. These results on the interface layer can explain the variation in the corrosion resistance. Copyright © 2008 John Wiley & Sons, Ltd.     

FDTD simulation of wavelength conversion of ultrashort pulses utilizing intersubband absorption in AlGaN/GaN quantum wells

The four-wave mixing (FWM) characteristics of 500-fs pulses in nonlinear optical waveguides utilizing the saturation of the intersubband absorption at 1.55 μm in nitride multiple quantum wells are calculated by a one-dimensional finite-difference time-domain (FDTD) method combined with three-level rate equations describing the intersubband carrier dynamics. Efficiency for a 100-nm wavelength conversion in a 160-μm waveguide is predicted to be higher than 3% both for up- and down-conversions. The extinction ratio is higher than 20 dB. As for the short-pulse application, however, the conversion efficiency is strongly dependent on the phase difference between the pump and signal pulses, especially when the efficiency is high. This causes ambiguity in the output power. Therefore, the cross-loss-modulation (XLM) converter is preferable to the FWM converter for OTDM application. The FWM converters are considered to be applicable to simultaneous conversion of WDM signals.     

Electron-transfer polymers. XXXIX. Redox polymers based on duroquinonyl glycol

Redox polyurethanes, polyesters, and alternate copolyurethanes and copolycarbonates from two kinds of benzoquinonyl glycol were prepared based on 2-(duroquinonyl)-propan-1,3-diol. The oxidized polymer is stable. When the fully reduced polymer in solution is exposed to air the durohydroquinonyl residues are oxidized to the quinone form while the less substituted hydroquinonyl glycol residues remain stable in the reduced form. There is thus prepared polymer with oxidized and reduced groups alternating along the chain.     

Thermal and photochemical reactions of a stable thiobenzaldehyde, 2,4,6-tri-t-butylthiobenzaldehyde

Thermal and photochemical reactions of the title compound gave benzothiolane $\text{2}$ in high yield; the reaction with free radicals also afforded $\text{2}$ along with some other products.     

The microenvironment of DNA switches the activity of singlet oxygen generation photosensitized by berberine and palmatine

The effect of the interaction between DNA and the photosensitizer on photosensitized singlet oxygen (1O2) generation was investigated using DNA-binding alkaloids, berberine and palmatine. These photosensitizers were bound to DNA by electrostatic force. Near-infrared luminescence measurement demonstrated that the photoexcited alkaloids can generate 1O2 only when the photosensitizers are bound to DNA. A fluorescence decay study showed significant enhancement of the lifetime of their photoexcited state with the DNA binding. A calculation study suggested that the electrostatic interaction with DNA inhibits the quenching of the photoexcited state of these alkaloids via intramolecular electron transfer, leading to the prolongation of the lifetime of their excited state. This effect should enhance their intersystem crossing and the yield of energy transfer to molecular oxygen. The results show that the electrostatic interaction with DNA significantly affects the 1O2 generation activity of a photosensitizer. In addition, this interaction may be applied to the control and the design of photosensitizers for medical applications such as photodynamic therapy.