| Owing to their fantastic luminescence properties,such as large stokes,narrow emission spectra and long lifetimes,et al,lanthanide-containing polyoxometalates(Ln-POMs)have attracted considerable attention.Despite of their intriguing functionality,practical POM-based materials or devices are still not extensively developed because of coordianated water-induced luminescence quenching.Therefore,it is worthwhile to propose a supramolecular self-assembly approach to achieve the combination between POMs and organic components.This strategy is expected to optimize the luminescence properties of POMs,and regulate the functionalities of POMs through the synergetic effects of organic-inorganic components.Herein,by taking advantage of stimuli-responsive block copolymers possessing good designability,novel copolymer/Na9LnW10O36(LnW10,Ln=Dy,Eu)luminescent hybrids with controlled assembly and synergetic functionality are constructed.A novel photocleavable block copolymer PEO113-b-P(TEGMMA66-co-ClNPMMA36)bearing chloride-substituted o-nitrophenethyl carbamates was synthesized by ATRP.The copolymer underwent irreversible cleavage upon 365 nm UV irradiation to generate primary amine(pKa?8-9)residues which are completely protonated under a neutral pH in aqueous solution.Electrostatic attractions between the resulting positively charged copolymers and anionic LnW1 drove the formation of assemblies,which have a spherical shape with diameter of-20 nm.The microenvironments around LnW10 in the core of hybrid assemblies became highly hydrophobic,resulting in dramatically enhanced luminescence intensity.Low pH or high salt concentrations would decrease the final luminescence intensity after irradiation.A hybrid thermo-responsive sensor based on electrostatic and hydrophobic interaction was constructed by mixing UCST-type copolymer PEO113-b-P(AAm264-co-AN112-Co-DMAEMA8)with luminescent polyoxometalates EuW10.The copolymer showed an unexpectedly broad response to temperature as revealed by UV-Vis transmittance.Vesicles with an average diameter-255 nm formed by the copolymer/EuW10 complex at 5? were observed.As temperature ranged between 5? and 55?,the size of assemblies could be reversibly tuned.Benefitted from both hydrophobic interaction and electrostatic attraction provided by copolymer in cold water,EuW10 were encapsulated in highly hydrophobic cores,leading to an obvious enhancement in luminescence intensity.As temperature rose up,the luminescence intensity decreases.Furthermore,a linear decline in luminescence intensity of the complex at temperature ranging from 5? to 35? was obtained,showing a promising potential in thermal sensors.A thermo-and pH-dual responsive luminescent hydrogel on basis of electrostatic and hydrophobic interaction was successfully constructed by coupling the copolymer P(DEGMMA119-co-DMAEMA8)-b-PEO455-b-P(DEGMMAii9-co-DMAEMA8)with DyWio.Accompanying with an obvious sol-gel phase transition above the lower critical solution temperature(LCST),microenvironments around DyWio were subsequently changed from hydrophilicity to hydrophobicity,an enhancement in photoluminescence intensity of DyWio was observed.When temperature cooled down,the hybrid gel collapsed into sol,the luminescence could be restored.This luminescence-temperature relationship would be held for repeated trials.By addition of acid to protonate DMAEMA,electrostatic interaction between the positive copolymer and DyWio was extremely strengthened,and emission of DyWio was simultaneously enhanced.Sensitivity of DMAEMA to the pH change also enabled the emission of copolymer/DyWio complex to be reversibly switched by alternating acid/base treatments.Responsiveness of copolymer to temperature and pH contributes to the dual mediation on luminescent properties of POMs. |
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