Synthesis And Photoresponsive Behavior Of Supramolecular Gel Based On Azobenzene

Low molar-mass organic gelators(LMOG) are a kind of low molecular organic substance, which can aggregate three-dimensional networks and stop the flow of solvent, resulting in the formation of the gel. The azobenzene groups can change from trans- to cis-isomer under light irradiation, therefore, preparing the stimulus responsive organogels has important scientific significance and application value through introducing azobenzene groups in molecular skeleton of existing g elator by chemical modification. On the basis of literature review, this thesis designed and synthesized four azobenzene gelators with double melamine moieties. The critical gelation temperature and critical gelation concentration were investigated. The photoresponsive behavior of the gel and the effect on the morphology of aggregates under UV light irradiation were researched. The details are summarized as follows:1) The four gelators were prepared with the 4,4?-dihydroxyazobenzeneand 4,4'-azodibenzoic acid as raw material, and then have reaction with compound 3 and compound 4 respectively. Molecular structures of the four gelators were identified.2) The 4 gelators can form stable gel in common organic solvents with thermal reversibility. To the same types gelators, increasing the alkyl chain length can help to increase the gelation properties. Because of the difference in molecular structure, in the same solvent different gelator has different gelation property.3) The polarity of solvent has a greater influence on the microstructure of the gel. In polar solvents such as ethyl acetate, the diameter of fiber was relatively large, while in non polar solvents such as toluene and methyl cyclohexane, the diameter of fiber was small. It shows that the ability to self-assembly form the fibers is the key to the gel formation.4) Under the UV light irradiation, the speed that the azobenzene groups of M-AZO-1 and M-AZO-2 transform from trans- to cis-isomers is slower than that of M-AZO-3 and M-AZO-4. After UV light irradiation for 30 min, M-AZO-1 and M-AZO-2 can still gelate and little change occurs in the morphology of the aggregates, while M-AZO-3 and M-AZO-4 can't gelate in most solvents and the morphology of the aggregates change a lot. After gelators gelated, in the UV-vis absorption spectra of xerogel, the ?–?* transition band of trans azobenzene is blue shifted,comparing with the ?–?* transition band in chloroform solution. It shows that the gelators form the H-type aggregates.It can help to improve gelation properties and photoresponsive behavior by increasing the alkyl chain length in gelators and introducing alkoxy groups in the molecular chain. These results lay the experimental foundation of further exploration in controlling the transiton of gel to sol by transforming azobenzene groups from trans- to cis-isomers, and provide a scientific basis to the study on photoelectric device with melamine-azobenzene groups.