Synthesis And Organogelation Of Disc-shaped And Bent-core Dihydrazide Derivatives With Dialkyl-chains

Supramolecular self-assemble through noncovalent bond enable us an effective way to synthesize new functional“soft materials”.Compared to self-assemble system based on covalent bond,supramolecules show many advantages,such as reversible,structural diversity and easy to synthesize.Low molecular weight organogel based on intermolecular hydrogen bond is an important kind of organogel,which show potential applications in template,photoelectric device and drug delivery area.Herein,we designed and synthesized disc-shaped BP8-A and banana shaped BP0-C,BP6-C,BP8-C in order to investigate the effect of molecular structure,preparation conditions(such as incubation temperature and concentration)on the properties,behaviour of the organogels.1.BP8-A can gel many kinds of alcohol solvents(except methanol,MeOH).Hydrogen bonds between amide protons were confirmed to be the main driving force for self-assembly process of BP8-A comfirmed by temperature dependent ~1H NMR and FT-IR spectroscopy.BP8-A molecules aggregated in Col_h phase to give tangled fibers in its gel state in alcohol solvent.It was demonstarted that injection of certain amount of methanol to the solution of BP8-A in either benzene(Ben),chloroform(CHL),tetrahedrofuran(THF)or N,N-dimethylformaide(DMF)could result in sol-gel transition of the sols.BP8-A molecules aggregated into flat fibers in a way of rhombohetral,and corresponding xerogel films are hydrophobic with static contact angles of 160.0°,165.2°,163.7°in MeOH/CHL,Me OH/Ben,MeOH/THF system.In contrast,BP8-A aggregated in the way of Col_h phase in MeOH/DMF,which is similar to that in alcohol solvents.Both BP6-C and BP8-C can gel many kinds of organic solvents.Amide protons were confirmed to be involved in intermolecular H-bond as confirmed by ~1H NMR and FT-IR spectroscopy.Organogels of BP6-C in alcohols showed higher mechanical strength than gels of BP8-C in chlorofom.Xerogel of BP6-C exhibited tangled fibers with low crystallinity.Xerogels of BP8-C in alcohols showed crystalline bent-like structure.BP8-C gels formed in CHL and Tol are liquid crystalline gels,while gels formed in ethanol are crystalline gels.BP8-C organogels in chloroform showed higher cross-over strain to 200%indicating better elasticity.2.BP8-C could form two different kinds of gels depending on incubation temperature,i.e.,transparent gels at incubation temperature higher than 10 ~oC,and opaque gels at incubation temperature lower than 0 ~oC It took shorter time for gelation of BP8-C in chloroform with the decrease of incubation temperature.While,BP8-C could gel toluene(Tol)at temperatures higher than 0 ~oC,and the higher the incubation temperature,the shorter the gelation time.It was confirmed that supersaturation is the driven force for BP8-C gelation in CHL,while,diffusing process restrained the aggregation of the gelators in toluene.Kinetic study was carried out by fluorescence spectroscopy for BP8-C in CHL and Tol and the results indicated that fibers formed first,then bundled and tangled in CHL.Two-phase mechanism was found in BP8-C/Tol system.3.BP8-C showed an enantiotropic columnar mesophase.Xerogels of BP8-C in chloroform and toluene and ethanol showed different phase transition behaviours.BP8-C xerogels from ethanol showed thermotropic enantiotropic columnar mesophase,and those from chloroform and toluene exhibited glass transition,recrystallization,unknown mesophase and Col_h phase during heating,suggesting their polymeric feature.The different phase transitional behaviour are attributed to interaction between gelators and ethanol molecules which breaks down the supramolecular chains and resulted in shorter supramolecular chains in ethanol gels compared to those in toluene and chloroform,and weak intermolecular interaction still exist in isotropic state which enable gelators“remember”their initial state.