Synthesis,Properties And Applications Of Side Chain Liquid Crystalline Polymers With Aggregation-Induced Emission Enhancement Characteristics

Luminescent liquid crystals(LLCs)possess both orderliness of liquid crystals and excellent luminescent properties of fluorescent materials.The unique properties of fluorescent liquid crystals make them have wide applications in organic light-emitting diodes,light-emitting liquid crystal displays,polarized light-emitting materials and other fields.Although luminescent liquid crystals show great application prospects,the design and synthesis of fluorescent liquid crystals is still a big challenge.Up to now,most of the reported fluorescent liquid crystals behave concentration quenching effect,so it is difficult to integrate liquid crystal property and luminescent property in a one molecule.In this paper,a series of side-chain liquid crystal polymers with aggregation-induced emission enhancement characteristics(AIEE)were designed and synthesized using a-cyanostilbene as mesogen and fluorescent group for the first time.The influence of polymers chemical structures(flexible spacer length,alkoxy tail length and end group type)on the liquid crystal properties and luminescent properties of luminescent liquid crystal polymers was studied in detail.At the same time,we also explored the applications of the luminescent liquid crystal polymers in luminescent polymer organogels,multi-functional luminescent form-stable phase change materials and luminescent liquid crystal physical gels.The specific research work of this paper includes the following contents:(1)A series of AIEE luminescent liquid crystal monomers(Z)-6-(4-(1-cyano-2-(4-(alkoxy)phenyl)vinyl)phenoxy)hexyl methacrylate(M6PVPCm,m=1,2,4,6,8,10,12,14,16,18)and their corresponding polymers PM6PVPCm with different alkoxy tail length were designed and synthesized.The effects of alkoxy tail length on liquid crystal properties and luminescent properties of polymers were studied in detail.The results show that all monomers exhibit AIEE characteristics and all monomers are monotropic liquid crystal.PM6PVPCm with different alkoxy tail chain lengths can form stable double-layer smectic phase,and the clearing point temperature of PM6PVPCm shows increasing trend with increasing alkoxy tail length.All polymers also behave AIEE properties,and the solid-state fluorescence quantum yield of the PM6PVPCm varies with the alkoxy tail chain.The solid-state fluorescence quantum yield of the PM6PVPCm increases from 1.43%to 12.77%with the increase of the alkoxy tail length.(2)A series of AIEE luminescent liquid crystal monomers(Z)-?-(4-(1-cyano-2-(4-(octadecyloxy)phenyl)phenoxy)alkyl methacrylate(MmPVPC 18,m=0,2,4,6,8,10,12)and their corresponding polymers PMmPVPC18 with different spacer lengths were designed and synthesized.The effects of spacer lengths on liquid crystal properties and luminescent properties of polymers were studied in detail.The results show that the monomers with different flexible spacer lengths are monotropic liquid crystals,and all monomers exhibit AIEE characteristics.PMmPVPC18 with different spacer lengths can form stable double-layer smectic phase.With the increase of flexible spacer lengths,the clearing point temperature of the polymers decreases gradually.PMmPVPC18 with different spacer lengths also behave AIEE characteristics,and the solid-state fluorescence quantum yield of polymers increases with the increase of flexible spacer lengths.The solid-state fluorescence quantum yield of polymers increases from 3.34%to 16.89%with the increase of spacer length.(3)A series of AIEE monomers(Z)-(4-(1-cyano-2-(4-cyanophenyl)vinyl)phenoxy)alkyl methacrylate(MmPVPCN,m=2,4,6,8)and their corresponding polymers PMmPVPCN with D-?-A structure and different spacer lengths were designed and synthesized.The liquid crystal properties and luminescent properties of the polymers were studied in detail.The experimental results show that PM2PVPCN and PM4PVPCN with shorter flexible spacer are amorphous,while PM6PVPCN and PM8PVPCN with longer flexible spacer can form nematic liquid crystal.All polymers exhibit AIEE properties and all of them have higher solid-state fluorescence quantum yield.The solid-state fluorescence quantum yield of PMmPVPCN is closely related to its chemical structure.With the increase of spacer length,the solid-state fluorescence quantum yield of PMmPVPCN increases from 22.4%to 42.7%.At the same time,the polymer films also exhibit fast and reversible fluorescence response behavior.Under the irradiation of 365 nm UV light,the fluorescence intensity and the color of polymer films change.Under the irradiation of 254 nm UV light or heted at higher temperature,the fluorescence behavior of polymer films can be turned back to the initial state,which shows potential application prospects in optical information storage materials and anti-counterfeiting materials.(4)A novel supramolecular luminescent side-chain liquid crystal polymers P4VP(HPDPA)x were synthesized by solution blending and solution casting of hydroxyl-containing ?-cyanostilbene derivative(Z)-3-(4-(decyloxy)phenyl)-2-(4-hydroxyphenyl)acrylonitrile(HPDPA)and poly(4-vinylpyridine)(P4VP).When x>0.6,P4VP(HPDPA)x can form stable double-layer smectic phase.When x<0.6,P4VP(HPDPA)x are amorphous.The emission intensity of P4VP(HPDPA)x films decreases and the maximum emission wavelength shiftes to short wavelength with the increasing 365 nm UV irradiation time.P4VP(HPDPA)x films also show pH responsiveness.The emission intensity of P4VP(HPDPA)x films increases,and the maximum emission wavelength shiftes to long wavelength when added with alkali.The higher alkalinity it had,the greater its red shift.(5)A novel luminescent organogels materials were successfully prepared by"heating-cooling" method using luminescent liquid crystal monomers M6PVPCm and luminescent side chain liquid crystal polymers PM6PVPCm as gelators and using organic solvent as working materials.The effect of alkoxy tail length on luminescent organogels materials was studied in detail.Experimental results show that M6PVPCm and PM6PVPCm can form stable luminescent organogels in various solvents.The gelation ability of M6PVPCm and PM6PVPCm in organic solvents is related to the alkoxy tail length.The minimum gelation concentration(MGC)of M6PVPCm in organic solvents decreases with the increase of alkoxyl tail length.The MGC values of PM6PVPCm in organic solvents increases first and then decreases with the increase of alkoxyl tail length.The thermal stability of luminescent organogels is also related to the alkoxyl tail length.The TGS of organogels formed by M6PVPCm increases with the increase of alkoxyl tail length.The TGS of polymer organogels decreases first and then increases with the increase of alkoxy tail length.The luminescent behavior of photoluminescent organogels formed by M6PVPC18 and PM6PVPC18 is also show temperature sensitive and photoresponsive behavior.With the increase of temperature,the organogels breaks down and the emission intensity decreases.The trans a-cyanostilbene turns into cis ?-cyanostilbene with the application of 365 nm UV irradiation,resulting in the decrease of emission intensity of the luminescent polymer organogels.(6)A new type of multi-functional luminescent form-stable phase change materials was successfully prepared by "heating-cooling" method using luminescent side chain liquid crystal polymers PMmPVPC18 as gelator and paraffin as phase change material.The effect of spacer length on the properties of multi-functional luminescent form-stable phase change materials was studied in detail.Experimental results show that all polymers can self-assemble and form stable phase change materials in paraffin.With the increase of spacer length,the MGC of PMmPVPC18 in paraffin increases first and then decreases.The TGS and storage modulus(G')of luminescent form-stable phase change materials decrease with the increase of spacer length.With the increase of spacer length,the TGS of the luminescent form-stable phase change materials decreases from 152? to 64?,while the solid fluorescence quantum yield of the luminescent form-stable phase change materials increases from 4.97%to 16.54%.Compared with the other reported photoluminescent phase change materials,our prepared photoluminescent form-stable phase change materials have the highest energy storage density and solid-state fluorescence quantum yield.The phase change materials can be used as thermal energy storage materials,luminescent materials,ultraviolet shielding materials and agricultural films.(7)The side chain copolymers PM6PVPCN(x)-co-PM0ACB(y)were synthesized by copolymerization of luminescent monomer M6PVPCN and cyanobiphenyl acrylate MOACB.The liquid crystal properties,luminescent properties and gelation ability of PM6PVPCN(x)-co-PM0ACB(y)in small organic molecule liquid crystals 5CB were characterized in detail.The experimental results show that all the copolymers behave AIEE properties,and the emission intensity of copolymers in aggregation state is much stronger than in solution state.The liquid crystal properties and gelations ability of the copolymers are related to the copolymerization components of copolymers.When the molar content of the luminescent component is lower than 15%,the copolymers can form double-layer smectic phase and the copolymers can form stable luminescent liquid crystal physical gels in 5CB.When the molar content of the luminescent component is more than 15%,the copolymer can not form liquid crystal,and also can not form gels in 5CB.The properties of luminescent liquid crystal physical gels are also related to the composition of copolymers.The thermal stability and storage modulus of luminescent liquid crystal physical gels decrease with the increase of the luminescent component content.The electro-optic performance parameters of luminescent liquid crystal physical gels such as threshold voltage,saturation voltage and contrast decrease with the increase of the luminescent component content,while the off-state transmittance and the off-state response time increase with the increase of the luminescent component content.The transmittance and emission intensity of the luminescent liquid crystal physical gels can also be controlled by electric field,so it can be used as an electrically controlled fluorescent device.