Multistimuli-responsive Organogels Based On Hydrazide And Azobenzene Groups

Organgel is a kind of low molecular weight gelators dissolved in the solvent,to form a fiber network structure through the intermolecular hydrogen bond,π-πinteraction,van der Waals force,etc,and futher,to form self-assembled soft materials.The difference of gelators in molecular lengths,conformation,functional groups,etc.has a significant effect on the gelation and responsiveness of the gel.Therefore,the function of the materials can be enriched by the design of the gelators.For example,it could be add multiple functional groups in a molecule,and then the materials formed from the functional molecules maybe respond to the external stimuli,such as light,electricity,sound,ion,acid,alkali,and temperature.Based on this,we selected the Dn and En containing hydrazide and azobenzene derivatives to research their different gelation and multiple responsiveness.The main research contents are as follows:1.The organogels behaviours and the photo-responsive properties of Dn with different length terminal chains were studied.D7 only can form stable organogel in cyclohexane,D8 can form gel in1,2-dichloroethane and cyclohexane,whereas D10 can form gel in dimethyl sulfoxide,1,2-dichloroethane and cyclohexane,and the transition temperature of gel-sol was higher than that of D7 and D8,which indicate that the long terminal alkyl chain could improve the gelated ability and thermodynamic stability.Under the UV light irradiation,trans-azobenzene in Dn can transform into cis and this photoisomerization in the solution was very significant,but the photoisomerization of azobenzene in the gel state could not induce the gel-sol conversion.2.The behaviors of organogels and the multistimuli-responsive properties based on hydrazide and azobenzene units connected via different flexible central spacer(En,n=5,6,10)were studied.E6,E10 can form a stable gel with fiber network aggregation in DMF and the critical gel concentration of E10 is higher than E6,but E5 can not form gel.This behavior may be most attributed to the dependence of the molecular shape on the parity of the spacer considered in the all-trans conformation.E5 with an odd-numbered spacer,the molecules are inclined with respect to each other giving a bent-shaped motif.Meanwhile,the dipole moment value of E5 with bent-shaped motif increases,which improves the solubility of the E5 in DMF(polar solvent)and thus disturbs the aggregation of the E5 molecules,so the increase of the dipole moment value may be another reason for the gelation behavior.Organogels exhibit multistimuli-responsive properties,such as temperature,light,anions,and p H.The organogels showed photoinduced gel-to-precipitate transition under the irradiation by λ=365 nm UV light irradiation,which was attributed to the photoisomerization of azobenzene.The trans–cis isomerization in gels further caused the morphological change from fibrous to globular aggregates.In addition,due to the deprotonation of hydrazide group,upon addition of anion(F~-and Ac O-)or base(Na OH),the gel can show both color change and gel-sol transition.The results of these studies can further understand the structure-property relationship of LMOG.3.The anion responsive properties of two-component organgel based on E5 and4-poxd-B8 gelator mixture(the molar ratio 1:1).The 4-poxd-B8 can form stable organogel with 3D cross-linking network in DMSO,E5 cannot form organogel,whereas the mixture of E5 and 4-poxd-B8 can form stable organogel.And it can be confirmed that there is no interaction between the 4-poxd-B8 and E5,as well as the 4-poxd-B8 and F~-.Upon addition of anion(Fand Ac O-)into the two-component organogel,the gel can show color change but not gel-sol transition.The F~-only can interaction between with E5 and F~-was same as that of E5 and F~-,the 4-poxd-B8 gelator only serve as a gelation.,the role of the4-poxd-B8 is to form 3D cross-linking network by self-assembling to support the solvent to form organogel and keep the organogel without disassembly in the presence of F~-.