Kazuhiro Yabuuchi

A new urea gelator: incorporation of intra- and intermolecular hydrogen bonding for stable 1D self-assembly

A new bisurea gelator derived from 2,6-diaminopyridine has been developed. It efficiently gelates common organic and liquid crystalline (LC) solvents by forming elongated self-assembled fibres in solvents. X-Ray crystallography and 1H NMR measurements reveal that two urea groups in pyridine-based bisurea compounds form different hydrogen bonding patterns. One of two urea units is involved in intramolecular hydrogen bonding with the pyridyl nitrogen, while the other urea unit forms bifurcated intermolecular hydrogen bonding. This hydrogen-bonded structure is key for the fibrous self-assembly along with the efficient gelation. In addition, LC gels based on the pyridine-based gelator exhibit good electrooptic properties. These results indicate that the pyridine-based bisurea compound is a good gelator not only effective in gelation but also useful as a component of functional soft materials.

Self-Assembly of a Pyridyl Derivative and its Silver Complex: Formation of a Liquid Crystalline Phase and Organogels

Abstract Self-assembling behavior of N,N′-didodecyl-3,5-pyridinedicarboxamide and its silver complex has been studied. They act as gelators in solution and gelate a variety of organic solvents. Though the silver complex exhibits lower gelation abilities for halogenated and aromatic solvents, long-term stability is achieved for ethanol and acetone gels. Moreover, the silver complex exhibits a smectic A phase on cooling while a single component of N,N′-didodecyl-3,5-pyridinedicarboxamide exhibits no mesomorphic behavior. The XRD pattern for the complex shows that the layer spacing of the SA phase is 37 A˚.

Raman Spectroscopic Study of Bis(Diphenylglyoximato)Metal Complexes Under High Pressure

Raman spectra of bis(diphenylglyoximato)metal complexes M(dpg)2 (M = Pt and Ni) under high pressure have been studied. The C = N stretching bands remarkably moved with increasing pressure. The relationship between the Raman shift and pressure is almost linear. The rates of increase in the Raman shift with pressure were determined. The platinum complex was more sensitive to pressure than the nickel complex, which is consistent with the pressure dependence of absorption spectra. The shear stress effect applied on the Pt(dpg)2 thin film was quantitatively estimated by using the relationship between the Raman shift and pressure.

Photoinduced reinforcement of supramolecular gels based on a coumarin-containing gelator

The mechanical strength of supramolecular gels is usually low compared to that of cross-linked polymer gels, which sometimes limits practical applications of supramolecular gels. We report here photoinduced reinforcement of supramolecular gel structures using photodimerization of coumarin moieties introduced on a trans-(1R,2R)-1,2-cyclohexanediamine-based gelator. UV irradiation (λ > 300 nm) of toluene gels containing mixtures of trans-(1R,2R)-1,2-cyclohexanediamine-based gelators with and without coumarin moieties induced an enhancement in both the thermal and mechanical stabilities of the gels.