| Liquid crystal(LC)possessing excellently adaptive property and processability,is regarded as a smart soft material with great development potential.Compared with conventionally neutral LC,ionic liquid crystal(ILC)is a fascinating LC material solely composed of cation and anion.Moreover,it exhibits synergistic characteristics of LC and ionic liquid(IL),and the advantages involving flexible composition and controllable property,etc.Recently,employing the ionic self-assembly is an effective strategy to develop novel ILC compounds including surfactants and specific units.Notably,the ILC with diverse performances can be constructed according to the actual needs,and the phase structues can be adjusted by changing the surfactant moiety.Gemini surfactants display unique structural variations and favorable self-assembly abilities in comparison with traditional surfactants.In particular,certain ionic Gemini surfactants can stack into ordered thermotropic LCs,however,the monotonous phase structures and the lack of functions seriously hinder the further development.In this thesis,we introduced functional groups into multiple sites of quaternary ammonium salt-type cationic Gemini surfactant or made use of it with functional group via electrostatic interaction,thereby fabricating a series of emerging ILC materials.And we investigated the self-assembly process and mechanism in detail,and revealed the relationship among Gemini surfactant structure,the LC phase structure and macroscopic properties.The contents of this dissertation are as follows:In Chapter I,Introduction.The concept,driving force,classification,characteristics and research significance of self-assembly were briefly illustrated.The classification,structure,properties as well as functional applications of Gemini surfactants were comprehensively summarized.In particular,the relationship between the structure and surface activity,and the connection between the structure and aggregation behavior were emphatically highlighted.The definition,composition,phase structure,properties and importantly functional applications of ILCs were reviewed in detail.The construction strategy,building blocks,common phase structures and basic performances of surfactant-based ILCs were systematically described.Finally,the research theme,content and significance of the thesis were proposed.In Chapter II,combining the cationic Gemini surfactant dimethylene-1,2bis(alkyldimethylammonium bromide)(n-2-n·2Br)with FeC13,CeCl3 or GdCl3,magnetic Gemini surfactant(n-2-n·2X,X=Fe,Ce or Gd)were prepared for the first time.The study indicated that magnetic counterion endowed n-2-n·2Br with better surface activity,higher thermal stabity and various LC phase structure,diverse metal ions species determined the magnetic behavior,and the alkyl chain length influenced the magnetic intensity.After heating,n-2-n·2Fe could spontaneously self-assemble into ILC structures,which provided a neotype molecule magnet for fabricating smart LC devices.In Chapter Ⅲ,Gemini surfactant N,N-dimethyl-N-[2-(N’-alkyl-N’-glucose amide)ethyl]1-alkylammonium bromide(nGlu,where n represented the number of carbon atoms in each hydrophobic chain,n=12,14 or 16),was synthesized to construct multicolor circularly polarized luminescence(CPL)ILC system.nGlu could self-assemble into chiral smectic C(SmC*)phase structure in a wide temperature range,meanwhile,exhibited left-handed circularly polarized luminescence(L-CPL)behavior.During the self-assembly process,the effective clustering of the heteroatoms and functional groups endowed the ILC with dynamically tunable CPL color.In addition,the ILC could serve as chiral template and energy donor.After co-assembling with negatively charged fluorescent dyes,the chiral property and excited state energy effectively transfered from nGlu to these achiral molecules,thereby generating multicolor and white circularly polarized lights.Through coating the white luminescent ILC on a LED UV chip,a flexible light-emitting device could be conveniently fabricated for emitting white circularly polarized light.This work provided new insights for rationally designing fluorescent surfactants,opened up the pathways for achieving multicolor CPL characteristic in self-assembled systems,and contributed to propelling the development of flexible CPL devices.In Chapter IV,with the assistance of electrostatic interaction,we prepared a series of ionic complexs n-GMP by employing cationic Gemini surfactant n-2-n·2Br(n=10,12,14 or 16)and guanosine 5’-monophosphate disodium salt(GMP),which were regarded as chiral luminescent LC molecules.12-GMP could stack into tetragonal columnar(Colt)phase LC structure showing right-handed CPL(R-CPL)emission,while 14-GMP and 16-GMP could arrange in SmC*phases accompanying with L-CPL behaviours.Furthermore,K+or Sr2+triggered n-GMP to be G-quadruplexes with identical chirality,therefore,all ILC structures transformed into rectangular columnar(Colr)or Colt phases with R-CPL properties.The study suggested that adjusting alkyl chain length or introducing metal ion was effective method to control the LC phase structure and inverse the CPL signal.The work greatly broadened the pathway to constructing chiral luminescence mesogens,and provided a new strategy for developing biocompatible CPL-active materials.In Chapter V,six cationic Gemini surfactants having diverse spacers interacted with deprotonated L-amino acids to prepare CPL ILC materials.The study manifested that utilizing the same amino acid but changing the spacer structure,could effectively control the phase structure and inverse the CPL signal.Moreover,fixing the Gemini surfactant but employing diverse amino acids,could regulate the CPL performance.Due to the excitation wavelengthdependent luminescence property provided by amino acids,the CPL color of ILC could be reversibly switched among blue,cyan and green through regulating the excitation wavelength.This work provided a novel perspective for tuning the CPL property of LC materials,and paved a new avenue for conveniently constructing functional LC systems. |
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