POSS ionic liquid crystals

Abstract

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

Creative Synthesis of Organic–Inorganic Molecular Hybrid Materials

“…In addition, it was shown that POSS can contribute to the extension of the temperature range as an ionic liquid crystal. 125 Thermodynamic studies revealed that the structural features of the POSS core such as symmetry and steric shape should be responsible for unique thermal properties of POSS ILs such as the lower melting temperatures and the higher thermal stabilities.…”

Multi-stimuli responsive luminescent azepane-substituted β-diketones and difluoroboron complexes

“…Protonation and deprotonation of the nitrogen atom also make halochromism possible. Furthermore, many BF 2 bdks can be efficiently excited by both 1- and 2-photon absorption, to display bright, color tunable emission with quantum yields (ϕ) that approach unity, 24 and this research is improving upon their already desirable properties. Additional benefits of the azepane substituent include: 1) a large ε value contributes to high brightness (ε × ϕ), and 2) a strong amine donor can lead to red-shifted emission, expanding the set of achievable emission colors for multiplexing applications.…”

Recent progress in the development of advanced element-block materials

“…[32][33][34] As a result, room-temperature ILs, which are defined as ionic salts with a melting temperature below 25°C, were produced based on POSS. Based on these characteristics of POSS ILs, we next sought to transmit the POSS effect on thermal properties to the IL matrices via non-covalent bonds ( Figure 5).…”