| Since the1970s, when a formal definition of gels was given by Flory, soft materials have attracted increasing attention by all walks of life, in particular those from chemical and materials science communities, due to the special properties of gels based upon low-molecular mass gelators (LMMGs). It is the LMMGs that self-assemble into continuous3D networks via nonchemical bonding interactions, such as π-π stacking, coordination interaction, host-gust interaction, hydrogen bonding, dipole-dipole interaction, van der Waals interaction and electrostatic interaction etc. And the gel formed via the3D network immobilize a lot of solvents by capillary force and surface tension. Because of the interaction nature, the LMMGs-based gels are also called supramolecular gels. Compared with the chemical gels, the driving force of physical gels is weak and reversible, and thereby the physical gels possess smart responsiveness to external stimuli, such as heat, light, ultrasonic wave and shear stress, etc., resulting in gel-solution transitions, and even reversible phase transitions. In a word, gels are one of the most remarkable soft materials.Cholesterol (Chol) and its relevant compounds can be found everywhere in nature, and have been widely in creating LMMGs since it is equipped with good biocompatibility and multiple chiral center, rigid skeleton and strong π-π stacking. Studies revealed that cholesterol derivatives show strong tendency to gell various solvents, and the gels with them as LMMGs are superior in applications for the template preparation of micro-/nano-materials, and low-density but high strength materials.Considering the informations above mentioned and the research already conducted in our lab, it was hoped to develop new molecular gel systems with properties of potential applications in the future. Accordingly, a scorpion-shaped di-NBD (4-substituted-7-nitrobenzoxadiazole) derivative of Chol (Chol-2NBD) was designed and synthesized. Based upon this compound, a very smart thixotropic gel system was created. In addition, another compound (2CT-NBD) was also designed and prepared via utilization of click chemistry. Basically, this dissertation is composed of the following two parts.Firstly, a scorpion-shaped di-NBD derivative of cholesterol (Chol-2NBD) was designed and synthesized. The gelation behaviors of the compound in a series of single and mixed liquids were tested. It was shown that the compound is an effective gelator for mixed liquids of THF and benzene at room temperature and the gel shows a good thixotropic property. At the same time, mechanism and morphology of the gel were studied via SEM, XRD, FT-IR,1H NMR. Surprisingly, the injection moulding at room temperature with the gel might be possible, and furthermore, the fluorescence emission of the gel system is sensitive to the presence of ammonia gas. The nature of the sensing has been attributed to the weak interaction between the ammonia molecules and the nitro group of the gelator. It is expected that the gel system may be developed into a fluorescence sensor for the detection of ammonia gas.Secondly, considering the results described above and the work have already conducted in our lab, the poor gelling ability of Chol-2NBD to single liquids has been attributed to the too strong aggregation tendency of NBD unit in the compound, and thereby a new compound containing two Chol units and one NBD unit was designed. To be convenient, click chemistry was employed for the synthesis. Herein, the new compound also contains two triazole units. The gelation behavior, the mechanism, the rheological and other properties are under progress. |
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