Gelation, Colorimetic Fluoride-responsive And Photo-responsive Behaviour Of Azophenyl Hydrazide Derivatives

During the past few years, low molecular weight gels(LMWG) have attractedconsiderable attention as an elegant class of self-assembled materials. Numerousefforts have been devoted to the development of stimuli responsive gels, where theproperties of the system can be either switched on-off or tuned in the presence of anexternal or internal chemical or physical stimulus such as light, ionic strength, electricor magnetic fields, mechanical stress, pH changes, molecular recognition, ultrasoundand so on. Such responsive gel systems are highly desirable for the development ofsensor devices and have potential applications in chemical sensors, template synthesis,molecular recognition, drug delivery and release etc.. Based on our previous studies,we have synthesized a novel Azophenyl Hydrazide Derivatives Bn-NO2(n=12,14).The liquid crystalline behaviour, gelation behaviour and the photo-responsive andcolorimetric fluoride-responsive behaviour in solution and gel stat were studied. Theobtained results were outlined as follows:1, The compounds Bn-NO2exhibited an interdigitated smectic A phase. Apartfrom the lateral intermolecular hydrogen bonding, the synergistic dipole–dipoleinteraction arising from the strongly polar substituents (–NO2) and the sterichindrance effect induced by rigid azobenzene group were also the main factor for theformation of the SmAdstructure.2, We have studied the properties of the new super gelator B12-NO2. It showedan excellent gelation ability towards aromatic solvents such as benzene, xylene,toluene and chlorobenzene at very low concentrations. We also studied the thermalstability, morphology and structure information of B12-NO2gel and found that themain driving forces of the gel formation are intermolecular hydrogen bonds betweenamides, π-π interactions and van dar Wall interactions. At the same time, we also gavea possible molecular arrangement model in gel state.3, We have studied the photo-responsive behaviour of B12-NO2in solution and gel state. And we found that the365nm UV irradiation could not change the B12-NO2gel. However, through the research on photo-responsive behaviour of compoundB12-NO2and B12in solution state, we found that the hydrazide group directlyconnected azobenzene groups will affect the transformation ratio of B12-NO2fromtrans-to Cis-structure. But we cannot confirm whether the intermolecular hydrogenbonding will affect the photo-responsive property.4, The gel systems could selectively respond to F-and AcO-with gel-soltransition and color change. The different response behavior of gel on F-and AcO-isdue to the different solubility of TBA+salt with two ions in xylene. A possiblemechanism for the F-responsive process was proposed. The existence of twostepwise equilibria,(i) B12-NO2interacts with F-to give [BH·F]-complex, and (ii)the [BH·F]-complex interacts with a second F-and deprotonation takes place, withformation of [HF2]-and the five-membered ring based on intramolecular hydrogenbonding. The results might provide a strategy to design a novel gelator forconstructing stimuli responsive soft materials and provide the basis for thedevelopment of non-fluid systems for sensing anion with the naked eyes.