Do Anionic π Molecules Aggregate in Solution? A Case Study with Multi-interactive Ligands and Network Formation

An anionic π molecule can form an aggregate when a multi-interactivity is introduced, in sharp contrast to common anionic molecules that are generally difficult to stack on each other. We found that a multi-interactive ligand, 2,5,8-tri(4′-pyridyl)-1,3,4,6,7,9-hexaazaphenalenate (TPHAP⁻) exhibited a large Stokes shift and an intramolecular charge transfer, both of which were sensitive to hydrogen-bonding media. An anionic potassium salt of TPHAP⁻ in methanol formed various aggregation states depending on the concentration examined; this was revealed by steady-state spectroscopic and fluorescence lifetime measurements. Self-assembling cadmium ions and the ligands can create several morphological crystals that are controlled by the ligand concentration, among which three new structures were determined by single-crystal analysis. The X-ray structures obtained suggest that the aggregation states of the ligand in solution can be transferred to the solid system of the porous coordination networks.     

Solid–Gas Phase Synthesis of Coordination Networks by Using Redox-Active Ligands and Elucidation of Their Oxidation Reaction

Formation of coordination networks is a complex process affected by a multitude of factors. Many synthetic strategies have been developed that attempt to control these factors and direct the structure of the final product. Coordination bond formation and structural assembly processes, however, typically take place either in the solution or solid states. In comparison, gas-phase network synthesis remains largely unexplored. Herein, two new two-dimensional coordination networks are obtained from the solid–gas phase reaction between ZnX₂ (X=I, Br) and the redox-active 2,5,8-tri(4-pyridyl)1,3-diazaphenalene (HTPDAP) ligand. Their structures were solved by ab initio powder X-ray diffraction analysis and feature a novel Zn halide trimeric cluster. This strategy is contrasted with a conventional solvothermal synthesis, which led to a one-dimensional coordination polymer instead. The intrinsic electroactive properties of these materials were probed by solid-state cyclic voltammetry measurements, which revealed the presence of HTPDAP and halide-based processes. Chemical oxidation of the two-dimensional networks by using NOPF₆ agent, unexpectedly, led to the formation of a nitrated analog of HTPDAP, the PF₆⁻ salt of diprotonated 4,6,7,9-tetranitro-2,5,8-tris(4-pyridyl)diazaphenalene cation (denoted N-TPDAP), which was isolated and characterized. These results provide deeper insights into the oxidation process of HTPDAP-containing networks and uncover unique redox-induced chemical transformations.     

XPS study on surface modification of NiTi alloy by acidic solution immersion and subsequent heating in air

Changes in the surface chemical state of a nearly equiatomic nickel–titanium (NiTi) alloy caused by immersion in aqueous solutions of HNO₃ and H₂SO₄ as well as subsequent heating in air at 723 K were analyzed using X-ray photoelectron spectroscopy (XPS). An XPS analysis using angle-resolved technique and a mathematical deconvolution technique revealed that a passive layer formed in an ambient atmosphere contained TiO₂ as a major state and Ni(OH)₂ and NiO as minor states. The Ni(OH)₂ on the alloy remained in the region even when heated in air at 723 K. Therefore, the resulting layer became a Ti-oxide layer with Ni segregated region at the surface, which was NiO formed via dehydration of Ni(OH)₂. However, immersion in an aqueous solution of HNO₃ or H₂SO₄ enables Ni(OH)₂ state to dissolve in the passive layer of a NiTi alloy; thereby, the Ni segregated region rarely appeared in the oxide layer by heating. The Ni segregated region at the surface becomes an obstacle for the inward diffusion of oxygen; thus, the annihilation of such a segregated region results in an increase in the thickness of the oxide layer.     

Nonadiabatic nondegenerate excitation by optical near-field and its application to optical pulse-shape measurement

Using DCM dye grains and light of different wavelengths generated by two CW laser diodes that oscillate in the near-infrared wavelength region, visible light emission from dye grains due to near-infrared excitation based on a nonadiabatic, nondegenerate excitation process was observed for the first time. Unlike sum-frequency generation with nonlinear polarization, the difference in polarization angles of the two beams did not affect the emitted light intensity. Optical sampling based on this nonadiabatic, nondegenerate excitation principle was demonstrated for the first time. The optical pulse shape in the wavelength band of λ=1250–1350 nm, which is close to the wavelength range used for optical fiber communications, was measured with a temporal resolution of 0.8–1.1 ps.     

Comparison of surface films formed on titanium by pulsed Nd:YAG laser irradiation at different powers and wavelengths in nitrogen atmosphere

The nitridation of titanium (Ti) caused by a Q-switched Nd:YAG laser under nitrogen gas atmosphere was investigated in situ using X-ray photoelectron spectroscopy (XPS). A laser having a wavelength of 1064 nm and 532 nm (SHG mode) was irradiated on a titanium substrate in an atmosphere-controlled chamber, and the substrate was then transported to an XPS analysis chamber without exposing it to air. The characteristics of the surface layer strongly depend on the laser power. When the power is relatively low, a titanium dioxide layer containing a small amount of nitrogen is formed on the substrate. Laser irradiation beyond a certain laser power is required to obtain a stoichiometric titanium nitride (TiN) layer. A TiN layer and an oxynitride layer with a TiO_xN_y-like structure are formed as the topmost and the lower surface layer, respectively, when the laser power exceeds this threshold value. The threshold laser power strongly depends on the wavelength of the laser, and this threshold value for the 532-nm laser is quite lower than that for the 1064-nm laser.     

Absorption Spectra of Planarian Visual Pigments and Two States of the Metarhodopsin Intermediates

Abstract— Absorption spectra measurements of isolated planarian ocelli by a microspectrophotometer (MSP) and intra-ocellar recordings of the early receptor potential (ERP) were carried out in order to characterize in situ planarian rhodopsin (pRh) and its photoproducts. The MSP spectra of the isolated ocelli revealed Λ_max at about 500 nm. The ERP evoked by a test stimulus was a positive monophasic waveform in the dark but became negative during exposure to violet light. During subsequent darkness, the ERP rapidly reverted to a positive waveform but with a smaller amplitude than before exposure. The ERP amplitude recovered to its initial level upon exposure to red light. The ERP experiments suggest that pRh produces two metarhodopsin intermediates, with Λ_max longer than that of pRh: the metastate responsible for the negative ERP converts to another metastate that results in a smaller ERP in the dark-adapted ocellus.     

Evaluation of the dynamic range and spatial resolution of nonadiabatic optical near-field lithography through fabrication of Fresnel zone plates

Fresnel zone plates (FZPs) were fabricated in order to evaluate the performance of nonadiabatic photolithography by exploiting the localized nature of optical near fields. This novel photolithography scheme could realize FZPs with structures smaller than the wavelength of the light source used for exposure. The FZP for 325-nm-wavelength UV light could focus the incident light to a spot size of 590 nm. An FZP for focusing soft X-rays was also fabricated and, compared to conventional adiabatic photolithography, showed higher-contrast zones over the whole area of the FZP. This method exhibits a high dynamic range and good spatial resolution, and it was free from artifacts due to the interference of the residual propagating exposure light transmitted through the aperture of the photomask.     

Second-harmonic generation of an optical frequency comb at 1.55 microm with periodically poled lithium niobate

To expand the span of the optical frequency comb (OFC), we generated the second harmonics of an OFC at 1.55microm , using a multiperiod periodically poled lithium niobate (PPLN) crystal. A coupled-cavity OFC generator with an average output power of 0.2 mW was amplified and expanded with a fiber amplifier and a dispersion-flattened fiber. The fundamental OFC average power and span were 100 mW and 45 THz, respectively. The second-harmonic comb's span was 3.2 THz; however, we tuned the center frequency over 30 THz by changing the poling period. We also demonstrated that the second-harmonic comb can be used for frequency-difference measurement.     

Biodegradable thermoresponsive poly(amino acid)s

Reaction of poly(succinimide) with a mixture of 5-aminopentanol and 6-aminohexanol produced new thermoresponsive polymers based on biodegradable poly(amino acids)s, poly(N-substituted alpha/beta-asparagine)s, showing a clear LCST in water.