The Effect of Branching on the One- and Two-Photon Absorption,Cell Viability,and Localization of Cationic Triarylborane Chromophores with Dipolar versus Octupolar Charge Distributions for Cellular Imaging

Two different chromophores, namely a dipolar and an octupolar system, were prepared and their linear and nonlinear optical properties as well as their bioimaging capabilities were compared. Both contain triphenylamine as the donor and a triarylborane as the acceptor, the latter modified with cationic trimethylammonio groups to provide solubility in aqueous media. The octupolar system exhibits a much higher two-photon brightness, and also better cell viability and enhanced selectivity for lysosomes compared with the dipolar chromophore. Furthermore, both dyes were applied in two-photon excited fluorescence (TPEF) live-cell imaging.     

Effects of discharge mode and gas composition for plasma-hydrophilized titanium surface on hydrophilic sustainability

Plasma hydrophilization under various conditions was carried out on Ti substrates to investigate the effect of the applied parameters on the hydrophilic sustainability. The plasma was discharged from gases comprising Ar and/or O₂ at various ratios using DC and RF modes. Notable differences in the surface morphology by the plasma conditions was hardly found, while the ratio of hydroxide on the surface was influenced by the discharge mode. The hydrophilicity was significantly improved regardless of the treatment conditions, that is, the gas composition and discharge mode. The deterioration of the hydrophilicity was occurred by storing in the ambient atmosphere or distilled water, wherein the deterioration in distilled water was suppressed when using DC as a discharge mode. The hydrophilicity was preserved when the specimens was stored in a physiological solution such as phosphate buffered saline solution due to the adsorption of Na⁺ and Cl⁻ in the solution; its effect was far superior to that contributed by the parameter settings. In conclusion, plasma discharge mode enabled to improve the deterioration of hydrophilicity only slightly.     

Effects of Amino Group Substitution on the Photophysical Properties and Stability of Near-Infrared Fluorescent P-Rhodamines

A series of phosphine oxide-bridged rhodamines (P-rhodamines) bearing various acyclic and cyclic amine moieties, including dimethyl- and diethylamine, azetidine, pyrrolidine and 7-azabicyclo[2,2,1]heptane (7ABH), have been synthesized. The photophysical properties as well as chemical and photostability of these dyes have been studied in detail. Among these dyes, the 7ABH-substituted dye shows stronger fluorescence in the near-infrared (NIR) region, relative to the other P-rhodamines. This dye could be applied to live-cell imaging, wherein lysosomes were selectively stained in a pH-independent manner. It was also found that the ring fusion of the amine moieties gives rise to remarkably redshifted spectra, with absorption and emission maxima at 770 and 820 nm, respectively, spectrally close to that of indocyanine green (ICG). Importantly, the ring-fused P-rhodamines showed much higher photostability than ICG, indicative of their promising utility as the NIR-emissive dyes.     

XPS study of a laser-nitrided iron surface using a focused pulsed Nd:YAG laser under various conditions

Laser nitridation of a pure iron (Fe) surface was conducted using a focused pulsed Nd:YAG laser under a nitrogen atmosphere, and the effects of nitrogen gas pressure, laser power, and repetition number of laser shots on the surface characteristics were analyzed using XPS. The laser-irradiated surface consisted of the topmost surface layer of Fe oxynitride (FeO_xN_y) and the underlayer beneath, which mainly comprised Fe nitride (Fe₄N). The topmost surface layer is a post-formed layer due to the oxidation of the nitride layer. The thickness of the underlayer corresponding to the original nitride layer drastically increased under nitrogen gas at atmospheric pressure. Increasing the repetition number of laser shots enhanced layer thickness up to 5 shots, after which no change was observed. Moreover, the layer thickness increased monotonically with increasing laser power. Nitridation through pulsed laser irradiation was likely predominated by the melting and resolidification of a specific surface area, as well as the convection of nitrogen therein. Thickness variation under various conditions can be explained appropriately using this assumption.     

Catalytic Four‐Electron Oxidation of Water by Intramolecular Coupling of the Oxo Ligands of a Bis(ruthenium–bipyridine) Complex

A bis(ruthenium–bipyridine) complex bridged by 1,8‐bis(2,2′:6′,2′′‐terpyrid‐4′‐yl)anthracene (btpyan), [Ru₂(μ‐Cl)(bpy)₂(btpyan)](BF₄)₃ ([ 1 ](BF₄)₃; bpy=2,2′‐bipyridine), was prepared. The cyclic voltammogram of [ 1 ](BF₄)₃ in water at pH 1.0 displayed two reversible [Ru^II,Ru^II]³⁺/[Ru^II,Ru^III]⁴⁺ and [Ru^II,Ru^III]⁴⁺/[Ru^III,Ru^III]⁵⁺ redox couples at E_1/2(1)=+0.61 and E_1/2(2)=+0.80 V (vs. Ag/AgCl), respectively, and an irreversible anodic peak at around E=+1.2 V followed by a strong anodic currents as a result of the oxidation of water. The controlled potential electrolysis of [ 1 ]³⁺ ions at E=+1.60 V in water at pH 2.6 (buffered with H₃PO₄/NaH₂PO₄) catalytically evolved dioxygen. Immediately after the electrolysis of the [ 1 ]³⁺ ion in H₂¹⁶O at E=+1.40 V, the resultant solution displayed two resonance Raman bands at $\tilde \nu $ =442 and 824 cm^‐1. These bands shifted to $\tilde \nu $ =426 and 780 cm^?1, respectively, when the same electrolysis was conducted in H₂¹⁸O. The chemical oxidation of the [ 1 ]³⁺ ion by using a Ce^IV species in H₂¹⁶O and H₂¹⁸O also exhibited the same resonance Raman spectra. The observed isotope frequency shifts (Δ$\tilde \nu $ =16 and 44 cm^?1) fully fit the calculated ones based on the Ru? O and O? O stretching modes, respectively. The first successful identification of the metal? O? O? metal stretching band in the oxidation of water indicates that the oxygen–oxygen bond at the stage prior to the evolution of O₂ is formed through the intramolecular coupling of two Ru–oxo groups derived from the [ 1 ]³⁺ ion.     

Singular limit of a competition–diffusion system with large interspecific interaction

We consider a competition–diffusion system for two competing species; the density of the first species satisfies a parabolic equation together with an inhomogeneous Dirichlet boundary condition whereas the second one either satisfies a parabolic equation with a homogeneous Neumann boundary condition, or an ordinary differential equation. Under the situation where the two species spatially segregate as the interspecific competition rate becomes large, we show that the resulting limit problem turns out to be a free boundary problem. We focus on the singular limit of the interspecific reaction term, which involves a measure located on the free boundary.     

Fixed-distance coupling and encapsulation of heterogeneous quantum dots using phonon-assisted photo-curing

We propose a novel method of coupling heterogeneous quantum dots at fixed distances and capsulating the coupled quantum dots by utilizing nanometric local curing of a photo-curable polymer caused by multistep electronic transitions based on a phonon-assisted optical near-field process between quantum dots. Because the coupling and the capsulating processes are triggered only when heterogeneous quantum dots floating in a solution closely approach each other to induce optical near-field interactions between them, the distances between the coupled quantum dots are physically guaranteed to be equal to the scale of the optical near fields. To experimentally verify our idea, we fabricated coupled quantum dots, consisting of CdSe and ZnO quantum dots and a UV-curable polymer. We also measured the photoluminescence properties due to the quantum-dot coupling and showed that the individual photoluminescences from the CdSe and ZnO quantum dots exhibited a trade-off relationship.     

Controlling the size of ZnO quantum dots using the dressed photon–phonon-assisted sol–gel method

We developed a sol–gel method using the dressed photon–phonon (DPP) process. DPPs are selectively exited in nanoscale structures at photon energies that are lower than the bandgap energy, which allows one to increase the growth rate of smaller ZnO quantum dots (QDs). Thus, we obtained a smaller size variance of ZnO QDs. The growth rate was proportional to the power of the light used for DPP excitation. The results were confirmed using a rate equation that accounted for the concentration of the sol–gel solution.     

Synthesis and electrochemical properties of bipyrimidine bridged triruthenium complexes

A new μ(4)-bpym-bridged dimer of an oxoacetao-triruthenium complex with carbonyl, [{Ru(3)O(CH(3)COO)(5)(CO)(py)}(2)(μ(4)-bpym)], was synthesized. The complex possesses two stable mixed-valence states associated with Ru(3)(III,III,II)/Ru(3)(III,II,II) and Ru(3)(III,III,III)/Ru(3)(III,III,II). The IR-spectroelectrochemistry reveals ν(CO) spectra in five oxidation states, Ru(3)(III,III,III)-Ru(3)(III,III,III) to Ru(3)(III,II,II)-Ru(3)(III,II,II) and both the mixed-valence states show a spectrum indicating medium interaction between the Ru(3) units.