Self-assembled microstructures of an amphiphilic diarylethene featuring an alkyl chain and triethylene glycol groups showed a photoinduced reversible morphological change in water. Reversible photoisomerization of the core diarylethene gave rise to a reversible morphological transformation between colorless microspheres and colored fibers. When colorless microspheres were irradiated with UV light, colored fibers were formed, and when the colored fibers were irradiated with visible light, the spheres were restored to their original positions where the spheres originally existed. This system showed reversible morphological change through not only photoirradiation but also temperature change. These behaviors can be interpreted as a phase transition between the sphere and fiber states. The dynamic process of the phase transition was monitored by polarized optical microscopy (POM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). It was revealed that the formation of fibers upon UV irradiation occurred radially at the surface of the sphere and the formation of the spheres upon visible-light irradiation occurred at the middle of the fiber. The unique photoinduced mechanical motion provides useful information for the design of sophisticated photoactuators.

Two temperature-dependent structures of 2D and 3D Zn(II)-organic frameworks (ZOFs) with a new 5-substituted benzene-1, 3-dicarboxylic ligand, 5-iodoisophthalic acid (H2IIP), and an auxiliary flexible ligand, 1,4-bis(1,2,4-triazol-1-yl)butane (btb), with different motifs, have been investigated. Results show that when the reaction was carried out at room temperature, a undulating 2D (4,4)-network, {[Zn(IIP)(btb)]·4H2O}n (1), which further extends into a novel “soft” 3D supramolecular microporous framework with two kinds of 1D nanochannels supported by face to face π⋯π stacking interactions and C–I⋯I halogen bonds, was generated. Under hydrothermal condition at 170 °C, however, a two-fold interpenetrated 3D framework with α-Po network topology, [Zn(IIP)(btb)]n (2), would be obtained. Interestingly, both the right- and left-handed 21 helical water chains lie in one kind of the nanochannels in 1. When the auxiliary ligand was replaced by a less flexible one with a shorter spacer length, 1,3-bis(1,2,4-triazol-1-yl)propane (btp), a novel temperature-independent single-walled discrete coordination tube, {[Zn(IIP)(btp)]·2H2O}n (3), was obtained at the same two temperatures. Inside the tube is found the 21 helical water chain. Interestingly, the reversible desorption/adsorption behavior to water is significantly observed in the frameworks 1 and 3. The framework 1 falls within the category of “recoverable collapsing” and “guest-induced re-formation” frameworks. The result shows their potential application as late-model water absorbents in the field of adsorption materials. Remarkably, the first discrete single-walled Zn(II) coordination tube 3 shows high framework stability and exhibits reversible desorption/adsorption to some small guest organic molecules (methanol, ethanol and isopropanol). Furthermore, these compounds exhibit blue fluorescence in the solid state.

We report the synthesis, structural characterization, and functionality (framework interconversions together with proton conductivity) of an open-framework hybrid that combines Ca2+ ions and the rigid polyfunctional ligand 5-(dihydroxyphosphoryl)isophthalic acid (PiPhtA). Ca2[(HO3PC6H3COOH)2]2[(HO3PC6H3(COO)2H)(H2O)2]·5H2O (Ca-PiPhtA-I) is obtained by slow crystallization at ambient conditions from acidic (pH ≈ 3) aqueous solutions. It possesses a high water content (both Ca coordinated and in the lattice), and importantly, it exhibits water-filled 1D channels. At 75 °C, Ca-PiPhtA-I is partially dehydrated and exhibits a crystalline diffraction pattern that can be indexed in a monoclinic cell with parameters close to the pristine phase. Rietveld refinement was carried out for the sample heated at 75 °C, Ca-PiPhtA-II, using synchrotron powder X-ray diffraction data, which revealed the molecular formula Ca2[(HO3PC6H3COOH)2]2[(HO3PC6H3(COO)2H)(H2O)2]. All connectivity modes of the “parent” Ca-PiPhtA-I framework are retained in Ca-PiPhtA-II. Upon Ca-PiPhtA-I exposure to ammonia vapors (28% aqueous NH3) a new derivative is obtained (Ca-PiPhtA-NH3) containing 7 NH3 and 16 H2O molecules according to elemental and thermal analyses. Ca-PiPhtA-NH3 exhibits a complex X-ray diffraction pattern with peaks at 15.3 and 13.0 Å that suggest partial breaking and transformation of the parent pillared structure. Although detailed structural identification of Ca-PiPhtA-NH3 was not possible, due in part to nonequilibrium adsorption conditions and the lack of crystallinity, FT-IR spectra and DTA-TG analysis indicate profound structural changes compared to the pristine Ca-PiPhtA-I. At 98% RH and T = 24 °C, proton conductivity, σ, for Ca-PiPhtA-I is 5.7 × 10–4 S·cm–1. It increases to 1.3 × 10–3 S·cm–1 upon activation by preheating the sample at 40 °C for 2 h followed by water equilibration at room temperature under controlled conditions. Ca-PiPhtA-NH3 exhibits the highest proton conductivity, 6.6 × 10–3 S·cm–1, measured at 98% RH and T = 24 °C. Activation energies (Ea) for proton transfer in the above-mentioned frameworks range between 0.23 and 0.4 eV, typical of a Grothuss mechanism of proton conduction. These results underline the importance of internal H-bonding networks that, in turn, determine conductivity properties of hybrid materials. It is highlighted that new proton transfer pathways may be created by means of cavity “derivatization” with selected guest molecules resulting in improved proton conductivity.