High Efficiency Luminescent Liquid Crystalline Polymers Based On Tetraphenylethylene:Design,Synthesis,Photophysics Property,and Phase Structure

Luminescent liquid crystalline polymers(LLCPs)show extensive applications,such as liquid crystal displays,circularly polarized luminescent and optical information storage.However,most of the luminescent liquid crystal materials are inefficient in solid-state luminescence.Therefore,it is of great significance to design and synthesize new luminescent liquid crystal materials.In this work,the luminescent group tetraphenylethylene(TPE)with aggregation induced emssion(AIE)effect is introduced into the mesogen-jacketed liquid crystal polymer by covalent bond and non-covalent bond.Investigate the difference in liquid crystal structure and luminescence properties of different polymers and chemical chemical bonding bonds.The details are as follows:1.We designed and synthesized VTPEC4 and PVTPEC4,in which the TPE derivative was in the form of covalent bond(c-c single bond)to connect vinyl benzene.The chemical structure of the monomer and polymer were confirmed via 1H NMR,13 C NMR and MAIDI-TOF mass,GPC was used to determine polymer molecular weight and distribution.The thermal stability and phase structure was studied by TGA,POM,DSC,and one-dimensional wide-angle X-ray diffraction(1D XRD).The research results show that the monomer and polymer with good thermal stability.The monomer has no birefringence under polarized light indicating can’t form a liquid crystal phase.The polymer has a remarkable birefringence phenomenon and can form a smectic phase.In addition,the photophysical properties of the monomers and polymer were studied by ultraviolet absorption spectrometry(UV)and fluorescence emission spectrometry(PL).The results show that the monomer exhibit AIE phenomenon and the polymer exhibit aggregation-enhanced emission(AEE)phenomenon.However,the solid-state fluorescence quantum efficiency of the polymer is lower than that of the monomer,which maybe is due to the π-π stacking caused by the closed-packing structure.2.We designed and synthesized a hydrogen bond acceptor TPEPY,a hydrogen bond donor PPA,and a mesogen-jacketed liquid crystalline polymer(MJLCP)based on backbone via hydrogen bonding named PPA(TPEPY)x.The phase structure of the series complexes was studied by DSC,POM and 1D XRD.The results show that the molar ratio x of the hydrogen bond acceptor TPEPY has an important influence on the liquid crystal phase of the complex.With decreasing x,PPA(TPEPY)x show a phase structure change from hexagonal columnar phase(x ≥ 0.4)to columnar nematic phase(x=0.2).Meanwhile,both TPEPY and PPA(TPEPY)x have the AIE effect.More interestingly,the complex TPEPY content complex PPA(TPEPY)x exhibits different luminescence colors,with variation of the TPEPY content,the series of LLCPs show different colors,i.e.,the emission peak red-shifts from 500 nm(x = 1.0)to 530 nm(x = 0.2).The complexes have nonresponse to mechanical force because of the certain stability of hydrogen bonding.However,PPA(PTPEC4)x shows reversible fluorescence switching under acidic/basic vapors owing to the protonation effect.The simple filter paper sensor prepared by the complex can detect the protic acid with a Pka value less than 5.25 and the smaller Pka value shows the faster response time.