Synthesis And Properties Of Several Low Molecular Weight Organogelators

Low molecular weight organogels belong to the category of supramolecular chemistry.They are formed by self-assembly of low molecular weight organogelators.The main driving forces of gel formation are relatively weak non covalent bonds(such as hydrogen bonds,?-? interaction,van der Waals force etc),giving them sensitive properties to the external environment.In recent years,studies on the use of low molecular weight organogels for chemical sensing,oil spill treatment and treatment of toxic dyes in water have attracted widespread attention.Based on the previous works of our group,several low molecular weight organogelators were synthesized,and their applications in stimulating response and pollutant treatment in water were explored.The main results are as follows:(1)A new symmetrical dihydrazide derivative organogelator(MBH-10)with two dihydrazide units was synthesized.The gelation property and the self-assembly behavior were researched by FE-SEM,XRD,rheology,FT-IR and concentration-dependent 1H NMR,etc.Gels could be formed in acetonitrile and n-octanol with good mechanical properties.Quadruple hydrogen bonds between the dihydrazide units were viewed as the main driving force in the self-assembly process.The MBH-10 gelator which showed both anion-response(F-,H2PO4-)property and relatively green,efficient toxic dyes removal property might be used in the field of anion sensing and environment remediation in the future.(2)The synthesis and gelation properties of a series of organogelators containinga benzohydrazide unit and two alkoxy chains(o Bn)were reported herein.o Bn(n = 8,10,12)could form stable gels in commercial fuels(e.g.diesel),which were characterized by low critical gelation concentrations(CGCs)and good mechanical properties(G' > 105 Pa).The gelation process was further studied by FE-SEM,FT-IR and XRD,etc.It was demonstrated that in these organogels,molecules self-assembled into fibrils 3D-network,where,hydrogen bonding,van der Waals force and ?-?interaction were confirmed as the driving forces.As compounds o Bn(n = 8,10,12)show very good gelation properties in diesel,their application in oil spill treatment has also been tested.It was found that o Bn could achieve rapid(<30 s)and effective oil removal at room temperature,being good candidates for oil spill treatment in the future.The removal efficiency could be as high as 95%.(3)A new triphenylamine-based acylhydrazone derivative(TPAH-B8)was designed and synthesized.TPAH-B8 could form organogels in cyclohexane and ethanol with the treatment of ultrasound.A typical gelation induced fluorescence enhancement property was observed in cyclohexane gel which was attributed to the formation of J-aggregate in the gel state.More interesting,TPAH-B8 exhibited multi-stimuli responsive behaviors.Firstly,TPAH-B8 showed solvatochromic effect,with emission color changed from blue to cyan by changing the solvent from nonpolar cyclohexane to polar DMSO.Secondly,TPAH-B8 showed reversible mechanofluorochromism.The xerogel of TPAH-B8 from cyclohexane emitted blue fluorescence while the fluorescence color changed to cyan after grinding.The cyan and blue color could be repeated with the treatment of grinding and annealing,which was explored and ascribed to the transformation between crystalline and amorphous states.Thirdly,TPAH-B8 revealed acidochromic property.The fluorescence color of TPAH-B8 in organogel and solid states could be switched by trifluoroacetic acid(TFA)/triethylamine(TEA).(4)A pyridine-containing oxadiazole derivative(2-POXD-B8)was synthesized.It has a significant solvatochromic effect.2-POXD-B8 can form gel in methanol and DMSO.The acid(TFA)response properties of three oxadiazole derivatives,Bp-OXD-B8,2-POXD-B8 and 4-POXD-B8 were compared in dilute solution.All three compounds were found to be responsive to TFA,and 2-POXD-B8 and4-POXD-B8 containing pyridyl groups were more responsive than Bp-OXD-B8 containing no pyridyl group.The Ksv values calculated by the Stern-Volmer equation are 928.9 M-1(Bp-OXD-B8),2492.3 M-1(2-POXD-B8),and 14395.9 M-1(4-POXD-B8),respectively.The introduction of the pyridyl group enhances the responsiveness of the oxadiazole system to TFA.These three compounds can achieve cyclic fluorescence switching by using TFA/TEA treatment in solid state(film).The gel-sol and fluorescence switching of 2-POXD-B8 and 4-POXD-B8 were also achieved by TFA/TEA treatment in gel state.Finally,4-POXD-B8 is taken as an example to realize data encryption and decryption.