Synthesis Of Cyanostilbene-based AIE Liquid Crystal Materials And Stimulus Response Research

In recent years,as a kind of material with excellent luminescence properties in the solid or aggregated state,aggregation-induced emission（AIE）materials have received a lot of attention from scientists.Among them,cyanostilbene derivatives are typical AIE materials,which are simple to synthesize and easy to modify.AIE liquid crystal materials with muti-stimuli responsive behaviors could be developed by introducing flexible chains and functional groups to the core of cyanostilbene.The methods provided a new strategy for the preparation of smart luminescent materials using in the fields of information storage,biodetection,chemical sensor,anti-counterfeit,et al.In this thesis,a series of stimuli-responsive AIE materials were prepared by combining the central unit of cyanostilbene with tetraphenylene,carbazole moieties through Knoevenagel condensation,Etherification,Mc Murry coupling,and Suzuki coupling reactions,respectively.The cyanostilbene derivative AIE molecular structures were characterized by nuclear magnetic resonance spectroscopy(¹H NMR,¹³C NMR),high-resolution mass spectrum（HR-MS）,and Fourier Transform infrared spectroscopy（FT-IR）.The thermodynamic and liquid crystal properties of the samples were investigated by differential calorimetry（DSC）and polarized optical microscope（POM）.The photophysical properties of samples were studied by UV-Vis absorption spectroscopy（UV-Vis）and photoluminescence spectroscopy（PL）.Under different external stimuli conditions:solvent,temperature,mechanical force,p H,et al,the luminescence intensity and wavelength of this class of AIE materials were investigated.The luminescent change regular of these samples was concluded.Theoretically,the geometric configuration and electron cloud distribution of the highest occupied orbital（HOMO）and the lowest empty orbital（LUMO）of the molecule were calculated by density functional theory（DFT）.The stimulus-response mechanisms were revealed from the perspective of intra-molecular charge transfer（ICT）.The main studies are as follows:（1）The luminescent liquid crystal molecules of DC-DBM8,DC-LBM8 and Py-CN-LBM8with cyanostilbene units were designed and synthesized.Their photophysical properties,liquid crystal properties and muti-stimuli responsive behaviors including solvent,force,temperature,p H,and trace water,were investigated.The results showed that these compounds exhibited excellent luminescence behaviors in both THF/H₂O mixed solution and solid state with obvious AIE effect.The samples had liquid crystal properties,among which DC-DBM8 and DC-LBM8showed the schlieren texture of nematic phase liquid crystal and Py-CN-LBM8 showed the mosaic texture of smectic phase liquid crystal.The samples also had mechano-and thermo-fluorochromic behaviors.Py-CN-LBM8 showed different emission wavelengths and intensities in different solvents,exhibiting an obvious solvent-dependent emission behavior.The results of theoretical calculations indicated that the stimuli-responsive behavior of the compounds was due to the ICT effect of the molecule.（2）The luminescent liquid crystal materials of TPE-CN-M8（single arm）and DBBCM8（double arm）with tetraphenylene core and cyanostilbene moiety as the arm was designed and synthesized.We investigated the samples’AIE effects,liquid crystal properties,stimuli-responsie behaviors under different polar solvents and temperature and voltage conditions.The results showed that the compounds had excellent luminescence,obvious AIE effect and solvent-dependent emission behavior in THF/H₂O mixed solutions and solid state.The results of theoretical calculations indicated that the compounds had an obvious ICT effect.TPE-CN-M8does not possess liquid crystal properties,while DBBCM8 forms columnar phase liquid crystal.After blending TPE-CN-M8 with nematic liquid crystal 5CB,chiral agent S811,it formed room temperature supramolecular luminescent liquid crystals.The fluorescence response behavior of the TPE-CN-M8 liquid crystals at different temperatures and voltages were studied.The results showed that the sample had obvious stimuli-responsive behavior to both temperature and voltage.（3）The fluorescent materials of KZ-CN-NO₂,KZ-CN-OH,KZ-CN-M8,KZ-CN-LBOH and KZ-CN-LBM8 using carbazole core and cyanostilbene groups as the arms was designed and synthesized.We investigated the samples’AIE properties,liquid crystal properties,electrochemical properties,stimuli-responsie behaviors under different polar solvents,mechanochromic behavior and temperature and voltage conditions.The results showed that the compounds all had obvious AIE effect and solvent-dependent emission behavior.KZ-CN-NO₂achieved mechanochromic response.After the sample was grinded,the fluorescent color changed from yellow to orange,and the quantum yield increased.KZ-CN-LBM8 showed the schlieren texture of nematic phase liquid crystal.In order to prepare polymer films with solid-state luminous performance,KZ-CN-M8 films were obtained through the cyclic voltammetry（CV）of the electrochemical method in acetylene and liquid crystal solutions,respectively.Among them,the KZ-CN-M8 showed obvious oxidation reduction peaks by electrochemical aggregation in acetylene solution.Compared with the spin-coating films,the fluorescent emission peak of the electrochemical polymerization thin film was red-shifted and the surface of the polymerization film was uniform.The obvious oxidation reduction peak was not observed in the liquid crystal electrolyte solution,but POM observed the fan-shaped focal cone texture of the cholesteric phase,which indicated that the S811 successfully induced the chiral helical structure of the KZ-CN-M8molecule in 5CB.DFT studies revealed that the enhancement of the conjugation effect,and the ICT effect increased,leading to the changes of fluorescent emission peak shift.