Stimuli-responsive liquid crystal physical gels (LCPGs) were fabricated by using the hierarchical superstructures of benzene-1,3,5-tricarboxamide macrogelators in a host nematic LC medium.

Herein, we have synthesized novel photopolymerizable dumbbell-shaped diacetylene liquid crystal (LC) monomers by locating a diacetylene dicarboxylic acid group at the center and chemically connecting swallow-tails, such as hydrophobic alkyl chains (abbreviated as ATDI) and amphiphilic biphenyl mesogens (abbreviated as BPDI), with bisamide groups. Major phase transitions of dumbbell-shaped diacetylene monomers were identified using differential scanning calorimetry (DSC), polarized optical microscopy (POM), and Fourier transform infrared spectroscopy (FT IR). Molecular packing structures were studied based on structure-sensitive wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) analyses. Mainly, due to nanophase separations and strong intermolecular hydrogen bonding, ATDI formed a low-ordered lamellar LC phase at room temperature. BPDI self-assembled into highly-ordered crystal phases (K and K) at lower temperatures below a low-ordered lamellar LC phase, in which BPDI were intercalated with each other to compensate the mutual volume differences. From the photopolymerization of ATDI and BPDI, it was realized that the topochemical reactions of dumbbell-shaped diacetylene monomers were closely related to their chemical structures as well as molecular packing structures.

The physical properties of supramolecular soft materials strongly depend on the molecular packing structures constructed by thermodynamically and kinetically controlled molecular self-assembly. To investigate the relationship between molecular function and selfassembled molecular packing structure, a series of diacetylene (DA)-based supramolecules was synthesized by chemically connecting flexible dendrons to DA with amide (aDA−D) or ester (eDA−D) functions. The three-dimensional (3D) organogel network of amide-functionalized aDA−D was prepared in both polar and nonpolar solvents due to the intermolecular hydrogen bonding. 3D networks of aDA−D can be further stabilized by topochemical photopolymerization. The self-healing behavior of aDA−D was observed in the sheet-like structure formed in n-dodecane by the hydrophobic interaction between the gelator and solvent. The wringing behavior of aDA−D was also demonstrated using the dynamic interaction of amide function with n-butanol solvent. Kinetically controlled and photostabilized 3D networks can be a key component from biomedical devices to soft robotic applications.

For the advancement in multi-stimuli responsive optical devices, we report the elaborate molecular engineering of the dual photo-functionalized amphiphile (abbreviated as AZ1DA) containing both a photo-isomerizable azobenzene and a photo-polymerizable diacetylene. To achieve the efficient photochemical reactions in thin solid films, the self-assembly of AZ1DA molecules into the ordered phases should be precisely controlled and efficiently utilized. First, the remote-controllable light shutter is successfully demonstrated based on the reversible trans-cis photo-isomerization of azobenzene group in the smectic A mesophase. Second, the self-organized monoclinic crystal phase allows us to validate the photo-polymerization of diacetylene moiety for the photo-patterned thin films and the thermo-responsible color switches. From the demonstrations of optically tunable thin films, it is realized that the construction of strong relationships between chemical structures, molecular packing structures and physical properties of the programmed molecules is the core research for the development of smart and multifunctional soft materials.

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