The Synthesis And Self-assembly Of Light-Sensitive Low-Weight-Molecular Gelator, And Its Properties

Nowadays, low-molecular-weight gelators have attracted considerable attentions in the supremolecular chemistry, because of its structural diversity, facile preparation, mild condition and easy functionalization. Generally speaking, the organogelators could be self-assembled into various dimensional morphologic superstructures in the organic solvents though noncovalent interactions such as H-bonding, van der Walls,π-πstacking ect. Meanwhile, the organogelator could be selectively functionalized with the introduction of desired moieties so as to build up target system with intriguing optical, electrical and magnetical properties that would facilitate its wide application in the industry.We have synthesized several series of low-molecular-weight organogelators based on salen, tribenzenepyrazoline, azobenzene, Schiff-base etc functional groups, and investigated their gelation properties, including their optics, morphologies and state transition etc, by the measurements of FT-IR, UV-vis, XRD and fluorescence emission spectra. The introduction of the functional groups into the organogelator would give rise up to unique optical properties, which might have potential applications in optical nanomaterials. Some creative results were obtained, and the main results were outlined as follows:1. Dicholesterol derivative consisting of salicylideneaniline moieties is synthesized and its gelation property is investigated in various organic solvents. It is found that it is a good organogelator that it could form stable gels in many organic solvents such as cyclohexane, benzene and toluene etc. With the help of SEM Xrd and optimized molecular model, it is believed that the organogelator molecules in the gel phase are self-assembled into the 1-D nanofibers with unimolecular packing, which further cross-links to form 3-D network. Moreover, strong green fluorescence in gel state could be observed and very weak fluorescence in sol state and solution is detected, proposing the existence of aggregation-induced-emission enhancement in the process of gelation formation. The fluorescence quantum yield of the gel is approximately 600 times than that of the solution. The AIE phenomenon is ascribed to a combination of the J-aggregate and the rotation restriction of single bond of the chromophores. Notably, organogelator molecules domestically exist in the NH form in pale white at room temperature, while it prefers the kinetically stable OH form in yellow at low temperature (77K). In all, reversible thermochromism through sol-gel-freezing circulation in the gel system is achieved. Its unique characteristic indicates its potential utility as a temperature-sensitive material. Furthermore, photochromism is also oberseved in this system, when the gel is irradiated under Uv-light, that the hydrogen atoms are translocated to the adjacent N atoms, resuling in the transformation of OH form to NH form. Thus, the organogel system based on the salen moiety might be used potentially in the field of devices and sensors.2. Two organogelators with tri-benzene-pyrazoline as the core have been prepared and their gelation properties are investigated in organic solvents. It is found that both 1 and 2, whoseα-ring of the tribenzenpyrazoline core are attached to with C12H25O- group, could form stable gel in alkane solvents. As could be seen from the SEM images, they have been self-assembled into fiber-like and rod-like morphologies, respectively. Through Xrd, UV-vis and IR measurements, their assembled models have been studied. And it is deduced that 1, which has amino group attached to its c-ring, is self-assembled layer by layer through H-bonds in dimeric existence to form fiber structure. The molecular length of 2 is compatible with the periodicity of the gel, proposing its monomeric stacking in the gel. Comparing with that of the solution, a redshift is observed in the UV-vis spectra in the gel, which is due to the formation nof J-aggregates.3. Three C3-symmetrical compounds with 1,3,5-benzenetricarboxylic acid as the core have been prepared with the introduction of light-sensitive functional groups viz. azo-benzene, Chartone, Schiff-base peripherally modified, in the hope of obtaining light-sensitive gel systems. It is found that 1 and 2 are good low-weight-molecular organogelator that they could form stable gel in organic solvents. It is studied that they have been self-assembled into plate and rod-like structures with unimolecular packing. It is found that 9 is hardly dissolvable in organic solvents and would like to precipitate from the cooling solution, resulting in failure of gel formation. Notably, it is observed that 9 possessed liquid crystal characteristics. Its liquid crystal behaviors have been investigated that it appears mesogenic behavior in the range of 200-300 oC, as observed by DSC and optical microscope.