| Holographic polymer/liquid crystal composites(HPLCCs),which are composed of alternative polymer and liquid crystal(LC)phases,are capable of recording the whole information of light(e.g.,amplitude and phase)by the periodical refractive index modulation.They have shown significant value for advanced anti-counterfeiting,highdensity data storage,augmented reality display and other high-tech applications not only because they are able to exhibit unique grating diffraction and responses to external stimuli(e.g.,electricity,light and heat),but also because they hold the excellent processability.On the other hand,tetraphenylethylene(TPE)derivatives,which hold the aggregation-induced emission and stimuli-response features,have been widely applied in the cutting-edge research fields such as biological imaging,electroluminescence,chemical sensing and security.Thus,the integration of TPE derivatives with HPLCCs is expected to produce new materials with more flourishing functions,which is of great significance for enhancing the development of high-security level anti-counterfeiting technologies.However,it remains challenging to design and synthesize TPE derivatives that can be compatible with HPLCCs and can also enable the synergy with the LC within composites.To tackle above challenges,the relationship between the chemical structures of substituents to the fluorescent emission of TPE derivatives was systematically studied in this dissertation,and effects of length and branching degree of alkoxyl chains of TPE derivatives on the photoluminescence of holographic polymer/LC composites were discussed.In addition,the photoluminescence behaviors of the composites were successfully regulated via the photocyclization of TPE unit.Furthermore,orthogonal storage,crosstalk-free display and cooperative-thermoresponse of holographic and fluorescent dual images were achieved in the HPLCCs by the synergy of citronellyloxyl TPE(denoted as TPE-4CN)with the LC,which paves a new way for multifunctionalization of the composites.Finally,thiols were introduced into the HPLCCs to drive the diffusion of TPE-4CN from the LC phase to the polymer/LC interface via the interfacial thiol-ene click reaction.This novel design simultaneously improved the thermosensitivity and contrast of dual images and also prolonged the lifecycle of the fluorescent image,which paves a new way to reconstruct high-security level anti-counterfeiting materials.Main results and conclusions are given as follows:(1)Electron push-pull effects on the photophysical properties and photocyclization behaviors were carefuly studided by using TPE,1,1,2,2-tetra-(4-methoxybenzene)ethylene(TPE-4MO)and 1,1,2,2-tetra-(4-nitrophenyl)ethylene(TPE-4NI)as the model compounds,respectively.Results show that the band gap between the highest occupied molecular orbital(HOMO)and the lowest unoccupied molecular orbital(LUMO)can be reduced by decorating electron-donating or electron-withdrawing groups on the TPE unit,resulting in redshift of both peak absorption and fluorescence emission of TPE derivatives.The electron cloud density of the reaction sites is decreased by the electron-withdrawing group,giving rise to the decline of photocyclization activity of TPE units.When decorated with electrondonating groups,the dihedral angle between adjacent benzene rings of the TPE unit is reduced and the reaction sites move closer to each other if exited to the first singlet state,leading to an improvement of the photocyclization activity of the TPE units.Therefore,the photocyclization rate is given as follows from high to low: TPE-4MO > TPE > TPE-4NI.(2)Chemical structure effects of alkoxyl chains on the fluorescent emission of both TPE derivatives and polymer/LC composites were systematically investigated.Results indicate that the compatibility of TPE derivatives with the LC can be improved by increasing the chain length and branches of alkoxyl groups.When the carbon number of the alkoxyl group is 2,the TPE derivative molecules are mainly located in the polymer phase within the composites.When the carbon number of the alkoxyl chain is increased to 6,they are uniformly distributed in both polymer and LC phases.When the alkoxyl chain is the branched citronelloxyl group,they are mainly enriched in the LC phase.Improving the compatibility of alkoxyl TPE with the LC is conducive to promoting the synergy between them,which thus results in redshift of the fluorescence emission of composites and faster photocyclization of the TPE unit.(3)Holographic polymer/LC/TPE-4CN composites were successfully fabricated and the effect of TPE-4CN/LC weight ratio on the composite fluorescence emission was analyzed.Results show that the grating diffraction efficiency of the composites remains above 90% when the weight ratio is increased from 0.00 to 0.10.At the same time,the luminescence color gradually changes from blue to yellow-green,and the absolute fluorescence quantum yield increases from 15% to 26% due to the synergy of the TPE-4CN with the LC,based on which holographic and fluorescent dual images with cooperativethermoresponse were integrated in a noninterfering manner.(4)Mercapto-decorated polymer/LC interfaces were successfully built by introducing thiol monomers during the reconstruction of holographic polymer/LC/TPE-4CN composites.Subsequently,TPE-4CN molecules were driven to diffuse from the LC phase to the interface by interfacial thiol-ene click reactions.The chemical fixation of TPE-4CN on the interface is found to excitingly improve the thermoresponse of both holographic and fluorescent images.Compared with the cases when enriching TPE-4CN in the polymer or LC phases,the composite emission intensity is increased by 0.8 and 2.3 times,the contrast ratio is improved by 0.9 and 0.2 times,and the maximum relative sensitivity is increased by2.8 and 1.0 times,respectively.Furthermore,the lifecycle of the fluorescent image can be prolonged by at least 12 times.These improvements are not only attributed to the fixation of TPE-4CN by the polymer network,but also ascribed to the synergy of TPE-4CN with the LC. |
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