Design Of Nayf₄-based Rare Earth Upconversion Luminescent Materials And Their Applications In Photodynamic Therapy,photocatalytic Degradation And Molecular Switching

Rare-earth upconversion luminescent materials follow the anti-Stokes law and have the advantages of near-infrared excitation,long luminescent lifetime,negligible autofluorescence,stable physical and chemical properties and low biological toxicity.The upconversion luminescent materials have shown irreplaceable application value in the fields of photocatalysis,molecular switching,biological imaging,medical therapy and so on.This paper focused on the design and preparation of upconversion luminescent particles and porous materials/polymer composites,and studied the structure-activity relationship among microstructure,luminescence properties and application properties of the composites based on upconversion luminescent particles,so as to realize the applications in photodynamic therapy,photocatalytic degradation and molecular switching.The main research contents of this paper are as follows:（1）In order to solve the problems of limited tissue penetration,low efficacy,and hypoxia in photodynamic therapy,a novel antibacterial agent UCNP@MC540@m Si O₂/Ag（UMSAg）was synthesized by coating large mesoporous silica with Na YF₄:Yb,Er@Na YF₄:Yb,Nd nanoparticles（UCNP）.The physicochemical properties,optical properties,drug loading rate,drug release and antibacterial properties of UMSAg were studied,and its antibacterial mechanism was analyzed.The results showed that the UMSAg achieved up to 9%loading rate of photosensitizer merocyanine 540（MC540）through the amide-bond combination of large mesoporous silica carrier and equal pore-size Ag particle,effectively avoiding the premature release of the photosensitizer.The UCNP emitted strong green light under near-infrared light（NIR）,activating the MC540 to produce singlet oxygen.In vitro antibacterial experiments,the amino group on the surface of UMSAg antibacterial agent quickly targeted bacterial membrane,and effectively achieved the dual antibacterial effect of Ag particles and reactive oxygen species under near-infrared light（980 nm）irradiation.The killing rates of UMSAg composite（150μg/m L）against drug-resistant Staphylococcus aureus and drug-resistant Pseudomonas aeruginosa were nearly 100%,which was significantly better than that of control group（UCNP@MC540@m Si O₂）.This work provides a good insight for the design of efficient antibacterial agents and has a potential application for the bacterial infection of deep tissues.（2）To address the issues of hydrophobicity of upconversion nanoparticles and limited targeting of photosensitizers,based on the above Na YF₄:Yb,Er@Na YF₄:Yb,Nd nanoparticles,the luminescence performance of Na YF₄:Yb,Er@Na YF₄:Yb@Na YF₄:Yb,Nd（UCNP）under NIR（808 nm）excitation was enhanced by introducing the energy-transfer layer（Na YF₄:Yb）as an intermediate layer.Further,a novel UCNP@DPS-ICG@m Si O₂-RB/mAb photosensitizer with high penetration and specificity was designed using DSPE-PEG2K-Silane functionalized UCNP combined with rose red photosensitizer（RB）and MMP14 monoclonal antibody（mAb）.The optical properties of upconversion nanoparticles and the dosage of DSPE-PEG2K-Silane,as well as the physical and chemical properties,drug loading rate,cell uptake,cell imaging,active oxygen release and photodynamic efficacy of the novel photosensitizer were studied.The results showed that the fluorescence performance of UCNP@DPS-ICG@m Si O₂ in aqueous phase was higher than that of UCNP cyclohexane phase through surface modification of DSPE-PEG2K-Silane and enhanced absorption of antenna molecular indocyanine green（ICG）.The UCNP@DPS-ICG@m Si O₂carrier achieved a high loading rate of 11.8%for the RB photosensitizer.Under NIR（808 nm）irradiation,UCNP@DPS-ICG@m Si O₂-RB/mAb nanoparticles produced plenty of singlet oxygen and improved the depth of photodynamictherapy.Comparedwithnon-targeted UCNP@DPS-ICG@m Si O₂-RB,UCNP@DPS-ICG@m Si O₂-RB/mAb showed increased singlet oxygen production and better photodynamic therapy effect,opening up a new approach for the treatment of bladder cancer.（3）In order to solve the problems such as limited photoresponse range,rapid recombination of photoinduced carriers and poor stability of photocatalysts in the degradation of organic pollutants,Na YF₄:Yb,Tm@Na YF₄:Yb,Nd@Ti O₂（Tm@Nd@Ti O₂）nanoparticles were anchored on the surface of porous silica/carbon（m SC）electrospun fibers to prepare a broadband photocatalyst（Tm@Nd@Ti O₂/m SC）.The dispersibility of Tm@Nd@Ti O₂ particles on the surface of the Tm@Nd@Ti O₂/m SC composite and its optical,adsorption,photocatalytic and cycling properties were mainly studied,and its photocatalytic and degradation mechanism were analyzed.The Tm@Nd@Ti O₂ nanoparticles absorbed near-infrared light/visible light and emited ultraviolet light to supply Ti O₂ shell,effectively realizing energy transfer between Na YF₄:Yb,Tm@Na YF₄:Yb,Nd and Ti O₂.The obtained Tm@Nd@Ti O₂/m SC composite with the interconnected mesoporous structure and carbon network was found to be beneficial in improving the adsorption capacity toward organic pollutants,promoting the separation of photogenerated carriers,and further improving the overall photocatalytic performance.The adsorption and photocatalytic activities of Tm@Nd@Ti O₂/m SC were evaluated by degradation of methyl orange（MO）solution.When the MO concentration reached 200 mg/L,the Q_max value of Tm@Nd@Ti O₂/m SC composite was 196.4 mg/g,which is significantly higher than that of some carbon-based adsorbents.When the Ti O₂ content was only0.04 g/L,the MO degradation rate of Tm@Nd@Ti O₂/m SC was 3 times that of Tm@Nd@Ti O₂.This study shows a great potential of combining carbon-based support with upconversion luminescent materials to develop efficient broadband photocatalysts.（4）In order to solve the problems of limited penetration and great harm to materials and organisms of stimulated light for traditional photoresponsive materials,a novel adhesive with NIR responsiveness and reusability was prepared by combining Na YF₄:Yb,Tm@Na YF₄:Yb,Nd@Na YF₄（UCNP）with siloxane azobenzene polymer（PAzo）.The UCNP were uniformly dispersed in the matrix through strong hydrogen bonding between oleic acid on its surface and hydroxyl groups in the main chain of matrix.The photoisomerization,viscoelasticity,adhesion and recyclability properties of composite films under NIR irradiation at different power densities were studied,and the mechanism of NIR light driven manual molecular switches was analyzed.When the content of UCNP in the composite was 5%,its mechanical properties were best,and its tensile strength was increased by 26.6%than that of the PAzo.Under NIR irradiation,the internal UCNP in the composite film produced two-color light（ultraviolet light and blue light）,rapidly stimulating azobenzene molecules to achieve photoisomerization dynamic equilibrium.At high power（5 W/cm²）,the photoisomerization of trans to cis occurred in composite films,and the viscoelasticity of the composite films decreased significantly,and the maximum adhesion and adhesion energy were decreased by 35%and 64%compared with PAzo,respectively.However,at low power（0.5 W/cm²）,the photoisomerization of cis to trans was performed,and the adhesion properties of composite films remained basically unchanged.Moreover,the composite film still maintained good adhesion properties after 6cycles,and the desticking phenomenon occurred in the composite film irradiated by high power（10 s）in simulated applications.This study shows a great potential of developing NIR photocontrolled adhesives by combining azobenzene polymers with upconversion luminescent materials.