We report the synthesis of a stable room-temperature ionic liquid consisting of an octacarboxy polyhedral oligomeric silsesquioxane (POSS) anion and an imidazolium cation. The introduction of the POSS moiety enhances the thermal stability and reduces the melting temperature. From an evaluation of the thermodynamic parameters during the melting, it was found that the rigidity and cubic structure of POSS can contribute to the enhancement of these thermal properties.
We have previously reported a polyhedral oligomeric silsesquioxane (POSS)-based room temperature ionic liquid (IL) that shows a melting temperature below 25 1C. The connection of ion pairs to POSS can significantly improve the thermal stability and decrease the melting temperatures of the ion pairs. To understand the mechanism of these changes induced by POSS, we studied the thermal properties of POSS derivatives with variable numbers of imidazolium-carboxylate ion pairs. Initially, it was found that a modified POSS with a larger number of ion pairs could be a thermally stable, room temperature IL. From the series of thermodynamic and conformational analyses, we concluded that the star-shaped distribution of ion pairs originating from the cubic framework are necessary to express the characteristic changes in the thermal properties of ion pairs connected to POSS.
Here we report the use of unique organic − inorganic hybrid materials composed of octa-substituted polyhedral oligomeric silsesquioxane (POSS) cores as ionic liquid (IL) crystals. These materials have a wide temperature range in which they exist in liquid crystal (LC) phase because of the stabilizing effect of the POSS core. We synthesized ion pairs composed of alkyl chainsubstituted imidazolium and carboxylates of various lengths that were or were not connected to the POSS core; then the thermal properties of these materials were investigated. It was found that both ion salts and the octadecyl-substituted imidazolium ion pairs with or without connection to POSS could form LCs. Interestingly, the LC phase of the POSS-tethered ion salts was maintained until decomposition. In contrast, the octadecyl-substituted imidazolium ion salts that were not tethered to the POSS core showed a clearance point during heating. The highly symmetric structure of POSS contributes not only to the suppression of the molecular motion of the ion salts, but also results in the formation of regular structures, leading to thermally stable, thermotropic IL crystals. In addition, by using electrostatic interactions originating among ionic moieties, robust chiral structures can be produced. 3,4 Even a small quantity of chiral ionic sources can efficiently induce enantiomeric structures in a bulk sample, and ionic moieties can be assembled to form regularly ordered structures. 5,6 These well-ordered ionic moieties are expected to work as efficient cation carriers and scaffolds for ordering cations. These materials, which comprise closely assembled ionic species, can exhibit interesting optical and magnetic properties. Thus, new molecular designs for preparing thermally stable LCs composed of ionic species are needed to produce advanced functional materials.The concept of supported IL phases (SILPs) has been recently proposed. Several materials based on SILPs have exhibited important characteristics such as high ion conductivity and compatibility with organic reaction media; these materials have been used as templates for the formation of nanostructures. 1 Silica supports improve the thermal stability of LCs. 7,8 Carmichael et al. 9 have synthesized and explored silicon wafer-assisted SILP materials. They created layers with thicknesses between 10 and 21 nm of an ionic LC with [C 18 C 1 Im] [PF 6 ] on the planar wafer surface and found that the ionic LC formed a mesophase. Inspired by their work, Wasserscheid et al. 7 fabricated SILP materials using silicon nanoparticles and used them as supports for preparing mesoporous structures that could act as effective gasphase catalysts. 8 To construct advanced materials based on the concept of SILP materials, their properties must be fine-tuned according to preprogramed designs at the molecular level. A wide variety of
We describe here the facile preparation of conductive casting films consisting of mixed-valence tetrathiafulvalene (TTF) nanofibers. Self-assembled nanofibers of mixed-valence TTF with organic acid anions were grown during film deposition, and the conductivities of the resulting films were significantly altered by the type of the anion. In particular, the casting films containing heptafluorobutyrate, propanesulfonate, and undecanesulfonate work as semiconductors (10(-2) S/cm). It was revealed that anion species played a crucial role in the formation of the nanofibers and the morphology of the film was varied.
We describe here the facile methods for the stepwise regulation of the formation of tetrathiafulvalene (TTF) radical cation and the self-assembly to the mixed-valence state of TTF in various polymer films. The homogeneous polymer composites containing TTF and (1R)-3,3-dimethylbicyclo[2.2.1]hepta-2-one-1-triflate as a photoinduced acid generator in several kinds of conventional polymers were prepared, and the phototriggered conversion of TTF to radical cation via protonation in the films was executed. The amount of the TTF radical species can be controlled by the length of UV-irradiation time to the polymer composite films. In addition, the formation of the mixed-valence TTF can be observed in the composite films by annealing after UV irradiation when the glass transition temperature of the matrices was sufficiently higher than the reaction temperature during the photoirradiation. Finally, we presented the facile patterning method for preparing the composite with the concentration gradient of TTF radical and the mixed-valence TTF.
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