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 97.1 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.

Supramolecular complexes consisting of anionic polyoxometalate (POM) and chiral, cationic lipids are newly developed. They give nanofibers, helical ribbons, and nanotapes in organic media depending on the chemical structure of lipid molecules. Lipid ammonium groups exert significant influence on their photoreduction characteristics.

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 DH of 97.1 kJ mol À1 , which is almost double the conformational energy stored in cisazobenzene chromophores. Thus, the integration of photoresponsive ILs and self-assembly pushes the limit of solar thermal batteries.Ionic liquids (ILs) have received increased attention because of their unique physical and chemical properties, which can be tailored based on their component chemical structures. [1, 2] Along with the expanding areas of energy-related applications, [3] self-assembly [4] and interfacial phenomena [5] of ILs have pushed back new frontiers. In light of the studies on ILs in extending the bulk liquid phase to interfacial materials chemistry, the next challenge involves controlling their physical properties and functions based on the phase-transition phenomena between the ionic crystal (IC) phase and the IL phase. This phenomena is in line with the recent expectations for ILs to serve as heat storage materials. [6] Meanwhile, phase transitions between ILs and ICs usually occur below room temperature, [7] and obviously a new approach is required to control these thermodynamic phasetransition phenomena at temperatures above room temperature and to link them with distinctive functions. To achieve the objectives, photochromism of azobenzene chromophores emerges as a prime candidate.[8] Azobenzene units have been widely employed as molecular switches because of their high quantum yields and ability to undergo reversible trans-cis isomerization upon sequential absorption of two different wavelengths of light.[8] The photoisomerization of azobenzenes to a high-energy metastable cis isomer allows storage of photon energy in the form of molecular strain energy (ca. 50 kJ mol À1 ), [9,10] which can be released as heat in the course of the cis-trans thermal isomerization. These features rendered azobenzene chromophores potential candidates for the closed-cycle solar fuels, however, they have encountered the following major problems: Firstly, the exothermicity of 50 kJ mol À1 for cis-azobenzene is comparable or even smaller than the minimum gravimetric energy density desired for thermal storage materials (ca. 100 J g À1 ).[6]Secondly, the trans-cis photoisomerization of azobenzene chromophores is significantly suppressed within crystals, [11] and consequently it has been studied in solutions.[9] The photoisomerization in solution inevitably results in significant decrease in the volumetric energ...

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