Based On A Group Of Azobenzene Photochromic Gel And Its Self-assembled Nature Of The Study

The self-assembling of small functional molecules into supramolecular structuresis a powerful approach toward the development of new materials and nanoscaledevices. As a novel class of self-assembled materials, Organogels have receivedconsiderable attention in recent years because they can organize into regularnanoarchitectures through specific noncovalent interactions including hydrogen bonds,hydrophobic interactions,Ï€-Ï€interactions and Van der Waals forces. In thisdissertation, three series of azobenzene moiety contained gelators were designed andsynthesized. The morphology, mechanism of the gel formation and the packingfashion in the gel state were studied in details. The whole paper contains four parts asfollowing:1. Morphology and wettability tunable two-dimensional superstructureassembled by hydrogen bonds and hydrophobic interactions.1) Designed and synthesized a tripodal tris-urea derivative 1a, which containstriethylamine, three azobenzene moieties and three hydrophobic alkyl chains.1a has the ability for gelating a wide variety of organic solvents, such as1-butanol (n-BuOH), 1-methyl-2-pyrrolidone (NMP), chloroform, xylene, andn-hexane.2) The morphology of the xerogels strongly depends on the nature of the gelling solvents.The cooperation of hydrogen bonds, hydrophobic interactions andazobenzene-azobenzene aggregation ability seems to be the key point of the bilayerself-assembly.3) The wettability of the surface therefore strongly depends on the morphologyof the xerogel which is in turn controlled by the intermediate gelling solvent.This is the first example that the wettability properties of the surface of a lowmolecular assembly is tuned by solvents.2. Morphology tunable and photo-responsive properties in a self-assembledco-gel system. 1) Designed and synthesized two C₃-symmetrical compounds (LC10 and LC4)containing three azobenzene groups on the fringe. These two compounds cannot gel any organic solvents. When introduced a gelator G18 with the similarC₃-symmetrical core structure, the mixture of the two compound (LC10 orLC4≤20ï¼…) can form photo responsive co-gel in 1,4-dioxane.2) The sole G18 xreogel from both ethanol and 1, 4-dioxane mostly formsone-dimensional packing. The morphologies of the xerogels from the mixtureshow quite different packing fashion from. The homogeneous pearl-shapedspheres with many tightly packed "buds" were found in the xerogels.3) Because the large amount of the G18 molecules separate the LC10 moleculesby hydrogen bonds andÏ€-Ï€stacking between the trisurea core of LC10and trisamide core of G18, and leave azobenzene group disordered in themargin of the aggregate, the co-gel exhibits reversible photo isomerizationfrom trans to cis transition without breakage of the gel state.3. Stabilization of the mesomorphic phase in a self-assembled two-componentsystem.1) The thermotropic properties and mesophase structures of the self-assembledsole LC10 and LC10/G18 are investigated. We found that the mixture ofLC10 and G18 can also self-assemble through hydrogen bonds to formlyotropic LCs as well as LC physical gel.2) The combination of C₃-symmetrical azobenzene compounds with a gelator ofa similar structure performs lyotropic liquid crystal as well as liquid-crystallinephysical gel in a temperature range larger than that of sole compound, suggests that thecooperation of intermolecular interaction between ureaes and amides in thesecomponents stabilizes the mesophase of the assembly.3) This successful combination of specific intermolecular interactions for theforming new types of LCs will lead to the development of novel functionalsoft materials and also for the fundamental understanding of soft-matterself-organization. 4. A novel photo responsive chiral organogel based on azobenzene.1) A novel triarmed cis-1, 3, 5-cyclohexanetricarboxamides gelator AZO-C16,functionalized by three acylamino and three azobenzene moieties grafted withthree long alkyl chains was synthesized. The cooperative interactions ofhydrogen bonding,Ï€-Ï€interactions and van der Waals forces confirmed thecompound an effective gelator for most of the organic solvents.2) Electron microscopy and spectral studies show that the gel formation is due tothe aggregation of AZO-C16 molecules into helical fibres throughcooperative interactions of hydrogen bonding of amide moieties,Ï€-Ï€interactions of azobenzene groups and hydrophobic interactions of alkylchains.3) The gel is sensitive to light irradiation and performs photochromism andget-sol transition by UV irradiation at room temperature. The stimuliresponsive smart supramolecular system is important in biological application,molecular (drug) release system, sensors, molecular devices, etc. Thisresearch affords a good example for design and investigation of theenvironment responsive soft materials.