RESUMEN
The cold crystallization mechanism of 1-{[4'-(4â³-nitrophenylazo)phenyloxy]}hexyl-3-methyl-1H-imidazol-3-ium tetrafluoroborate ionic liquid crystal was investigated based on thermal analysis, structural analysis, infrared spectroscopy, and quantum chemical calculations. By conducting thorough structural characterization, we found that the prerequisite for cold crystallization is the irreversible molecular conformational alteration induced by the initial heating of the as-grown crystal into a smectic liquid crystal. The originally linear cation molecule bends and forms a step-stair conformation that persists throughout the subsequent heating and cooling processes as phase transition occurs from the crystal phase to the liquid crystal phase and then to the isotropic liquid phase. The formation of cold crystal occurs because of the choice of molecular stability over crystalline stability. Given the exothermic anomaly exhibited upon heating generic crystals to cold crystals, these findings demonstrate the promising potential of this ionic liquid crystal for thermal energy storage applications.
RESUMEN
Ionic crystals (ICs) of the azobenzene derivatives show photoinduced IC-ionic liquid (IL) phase transition (photoliquefaction) upon UV-irradiation, and the resulting cis-azobenzene ILs are reversibly photocrystallized by illumination with visible light. The photoliquefaction of ICs is accompanied by a significant increase in ionic conductivity at ambient temperature. The photoliquefaction also brings the azobenzene ICs further significance as photon energy storage materials. The cis-IL shows thermally induced crystallization to the trans-IC phase. This transition is accompanied by exothermic peaks with a total ΔH of 97.1â kJ mol(-1) , which is almost double the conformational energy stored in cis-azobenzene chromophores. Thus, the integration of photoresponsive ILs and self-assembly pushes the limit of solar thermal batteries.
