Supramolecularly engineered perylene bisimide assemblies exhibiting thermal transition from columnar to multilamellar structures

Perylene 3,4:9,10-tetracarboxylic acid bisimide (PBI) was functionalized with ditopic cyanuric acid to organize it into complex columnar architectures through the formation of hydrogen-bonded supermacrocycles (rosette) by complexing with ditopic melamines possessing solubilizing alkoxyphenyl substituents. The aggregation study in solution using UV-vis and NMR spectroscopies showed the formation of extended aggregates through hydrogen-bonding and π-π stacking interactions. The cylindrical fibrillar nanostructures were visualized by microscopic techniques (AFM, TEM), and the formation of lyotropic mesophase was confirmed by polarized optical microscopy and SEM. X-ray diffraction study revealed that a well-defined hexagonal columnar (Col(h)) structure was formed by solution-casting of fibrillar assemblies. All of these results are consistent with the formation of hydrogen-bonded PBI rosettes that spontaneously organize into the Col(h) structure. Upon heating the Col(h) structure in the bulk state, a structural transition to a highly ordered lamellar (Lam) structure was observed by variable-temperature X-ray diffraction, differential scanning calorimetry, and AFM studies. IR study showed that the rearrangement of the hydrogen-bonding motifs occurs during the structural transition. These results suggest that such a striking structural transition is aided by the reorganization in the lowest level of self-organization, i.e., the rearrangement of hydrogen-bonded motifs from rosette to linear tape. A remarkable increase in the transient photoconductivity was observed by the flash-photolysis time-resolved microwave conductivity (FP-TRMC) measurements upon converting the Col(h) structure to the Lam structure. Transient absorption spectroscopy revealed that electron transfer from electron-donating alkoxyphenyl groups of melamine components to electron-deficient PBI moieties takes place, resulting in a higher probability of charge carrier generation in the Lam structure compared to the Col(h) structure.     

Continuous particle separation in a microchannel having asymmetrically arranged multiple branches

A new method for continuous size separation and collection of particles in microfabricated devices, asymmetric pinched flow fractionation (AsPFF), has been proposed and demonstrated. This method improves the separation scheme of pinched flow fractionation (PFF), which utilizes a laminar flow profile inside a microchannel. In this study, multiple branch channels with different channel dimensions were arranged at the end of the pinched segment, so that the flow rate distributions to each branch channel were varied, and a large part of the liquid was forced to go through one branch channel (drain channel). In the proposed channel system, the flow profile inside the microchannel was asymmetrically amplified, enabling the separation of one-order smaller particles compared with PFF. After introducing the method, we examined the effect of the asymmetric amplification by controlling the outlet of the drain channel. Also, a mixture of 1.0 approximately 5.0 microm particles was separated, and erythrocytes were successfully separated from blood. The results indicate that the AsPFF method could be applied to the separation of much smaller-size particles, since more precise separation can be achieved simply by changing the geometries of branch channels.     

Nuclear magnetic resonance studies on the rotational and translational motions of ionic liquids composed of 1-ethyl-3-methylimidazolium cation and bis(trifluoromethanesulfonyl)amide and bis(fluorosulfonyl)amide anions and their binary systems including lithium salts

Room temperature ionic liquids (ILs) are stable liquids composed of anions and cations. 1-ethyl-3-methyl-imidazolium (EMIm, EMI) is a popular and important cation that produces thermally stable ILs with various anions. In this study two amide-type anions, bis(trifluoro-methanesulfonyl)amide [N(SO(2)CF(3))(2), TFSA, TFSI, NTf(2), or Tf(2)N] and bis(fluorosulfonyl)amide [(N(SO(2)F)(2), FSA, or FSI] were investigated by multinuclear NMR spectroscopy. In addition to EMIm-TFSA and EMIm-FSA, lithium-salt-doped binary systems were prepared (EMIm-TFSA-Li and EMIm-FSA-Li). The spin-lattice relaxation times (T(1)) were measured by (1)H, (19)F, and (7)Li NMR spectroscopy and the correlation times of (1)H NMR, τ(c)(EMIm) (8 × 10(-10) to 3 × 10(-11) s) for the librational molecular motion of EMIm and those of (7)Li NMR, τ(c)(Li) (5 × 10(-9) to 2 × 10(-10) s) for a lithium jump were evaluated in the temperature range between 253 and 353 K. We found that the bulk viscosity (η) versus τ(c)(EMIm) and cation diffusion coefficient D(EMIm) versus the rate 1/τ(c)(EMIm) have good relationships. Similarly, linear relations were obtained for the η versus τ(c)(Li) and the lithium diffusion coefficient D(Li) versus the rate 1∕τ(c)(Li). The mean one-jump distances of Li were calculated from τ(c)(Li) and D(Li). The experimental values for the diffusion coefficients, ionic conductivity, viscosity, and density in our previous paper were analyzed by the Stokes-Einstein, Nernst-Einstein, and Stokes-Einstein-Debye equations for the neat and binary ILs to clarify the physicochemical properties and mobility of individual ions. The deviations from the classical equations are discussed.     

Heat capacity of [Ni(OCH3)(acac)(CH3OH)]4 from 0.4 to 285 K: Spin interaction and tunnel-splitting of internal rotation of methyl group

The heat capacity of the tetranuclear nickel cluster complex, tetrakis [μ₃-methoxo-2,4-pentanedionato (methanol) nickel (2)], has been measured from 0.4 to 285 K. Contrary to the previous prediction by Bertrand et al.[6], that this complex exhibits an intercluster ferromagnetic spin coupling, the present heat capacity measurement shows no indication of the spin-ordering effect caused by the intercluster interaction at least down to 0.4 K. Instead, a heat capacity anomaly centered around 1.5 K with a shoulder at 0.5 K has been observed. This anomaly is well accounted for in terms of both a level splitting of the ground S = 4 state due to a uni-axial crystalline anisotropy and a tunnel-splitting of the rotational levels of methyl groups. The intracluster spin exchange constant J and the single-ion zero-field splitting parameter D are determined to be $\text{J}\text{hc}\text{= 7.0 cm}{}^{\mathrm{?1}}$ and $\text{D}\text{hc}\text{= 3.65 cm}{}^{\mathrm{?1}}$ (h being the Planck constant and c the speed of light in a vacuum). The temperature dependence of the effective Bohr magneton [6] is also satisfactorily accounted for on the basis of this model. The tunnel-splitting δ of the lowest rotational level of the four methyl groups belonging to methoxides is estimated to be $\text{δ}\text{hc}\text{= 0.4–0.7 cm}{}^{\mathrm{?1}}$ and the corresponding potential barrier V_o is found to be V_o = 1.9–1.5 kJmol^?1.     

Relativistic electron transport and confinement within charge-insulated, mass-limited targets

We present experimental results on the interaction of short-pulse ultra-high-intensity laser beams with small size (“mass-limited”) targets. Several diagnostics (X-ray spectroscopy, K_α and optical imaging of target rear side) have been simultaneously used in order to characterize the laser-generated fast electron transport and energy deposition into the target material. Our results show that fast electrons are effectively confined inside the target by the induced space charge. This electrostatic confinement opens new opportunities to create “Warm Dense Matter” states characterized by solid-state density and temperatures of the order of a few tens of eV.     

Synthesis and properties of optically active phosphine-boranes possessing an l-menthyloxy group

(SP)-9-Anthryl(l-menthyloxy)phenylphosphine-borane and (SP)-(1-l-menthyloxy)benzo[b]phosphole-borane were synthesized, and their structures were characterized by X-ray crystallographic analysis. The latter compound was reduced by lithium naphthalenide at −78°C with cleavage of the P O bond, and the subsequent reaction with electrophiles afforded the corresponding tertiary phosphine-boranes possessing good to excellent enantiomeric excesses.