| Organic fluorophores can serve as versatile tools for biological imaging,medical diagnosis and phototherapy.The theranostic properties of organic fluorophores are closely related to their photophysical process and photochemical reaction.In this dissertation,we designed and synthesized novel fluorescent molecules depending on the physical and chemical reaction processes that may undergo after light activation of the dye.And then the fluorophores were applied in corresponding field according to their characteristics.Fluorescence imaging in the near-infrared(NIR,600-900 nm)window has attracted heightened attention for its high sensitivity,high efficiency and least perturbing to the system.However,the photobleaching properties of organic fluorescence molecules greatly limit their application in some fields.In the second Chapter of this dissertation,we analyzed the path of photobleaching of fluorescent molecules,and found that the non-fluorescent triplet excited state(T1)was a critical stage for photobleaching.The fluorophores in their T1 can react with molecular oxygen,biomolecules,and solvent impurity by electron-transfer reactions or triplet-triplet energy-transfer process to produce a series of reactive oxygen species(ROS),which further inducing photoblinking and photobleaching.Based on this understanding,a self-healing fluorescence NPA-Cy5.5 was synthesized by covalent linkage of a triplet state quenching NPA to a widely used cyanine dyes Cy5.5.NPA-Cy5.5 exhibited significantly enhanced photostability in a mixture of water and DMF without depleting oxygen specially.Then the NPA-Cy5.5 was conjugated with an amphiphilic polypeptide,P(OEGMA)21-P(Asp)i6-iPr,to enhance the solubility and improve the biocompatibility simultaneously.Cell experiments have shown that PF can effectively improve the photostable and it's an efficient way to expand its application in biological imaging and may be a potential candidate for fluorescence-guided surgery,super-resolution microscopy,and real-time dynamic fluorescence observation.The reflection,scattering and absorption of the biological tissue seriously limit the penetration depth of the light in the tissue.In general,visible light can only penetrate the superficial layer of the skin,and it's unable to visualize the deeper information in the body.The maximum penetration depth of NIR-? is about 3 mm,which seriously hinders the detection of subcutaneous tumors.Fluorescence imaging in the second near-infrared(NIR-?,1000-1700 nm)window has attracted heightened attention for its higher tissue penetration depth and minimized intrinsic tissue autofluorescence,which significantly improves the fluorescence imaging accuracy and signal-to-noise ratio.In the third Chapter of this dissertation,we designed and synthesized a hydrophobic small molecule fluorescence probe(FS),which exhibited NIR-? absorption and fluorescence emission,as well as excellent fluorescence quantum efficiency.After binding FS with an amphiphilic polypeptide,the microprobe(PF)was obtained and the PF can be used for NIR bioimaging.Most researches in NIR-? fluorescent probe focused on the NIR-? imaging performance of the dyes and rarely attention was payed to the potential phototherapy.In this chapter,we studied the potential photothermal effects of PF,and found that the PF has excellent photothermal stability and photothermal conversion efficiency,which can effectively ablate tumor tissues under 808 nm laser irradiation,and realize photothermal therapy(PTT)guided by NIR-? fluorescence imaging.Boron-dipyrromethene(BODIPY)showed outstanding photophysical properties and can be modified with a heavy atom to improve the inter-system crossing(ISC).In Chapter 4,we increased the quantity of bromine atom to the BDP core further for the enhanced ISC and obtained the BDP-4Br.Compared with BODIPY,the singlet oxygen yield of BDP-4Br was significantly improved,and its fluorescence emission showed a significant redshift(110 nm)on the premise of no significant change in absorption.BDP-4Br has significant NIR-? fluorescence tailing emission,showing an excellent NIR-? fluorescence imaging capability.After highly effective encapsulation with an amphiphilic copolymer P(OEGMA)21-P(Asp)16,the as-fabricated polymeric micelles(P@BDP)exhibited superb photostability and favorable photothermal conversion efficiency upon irradiation with 730 nm or 808 nm laser.By contrast,the P@BDP showed significantly better photodynamic therapy under 730 nm than 808 nm.These results indicate that P@BDP was endowed with NIR-? bio-imaging and NIR-? image-guided cancer PTT/PDT synergistic therapeutic activated by 730 nm laser,and single PTT under 808 nm.In vivo results showed that tumor growth could be effectively inhibited under the irradiation of 808 nm and 730 nm laser,but the treatment with 730 nm light could effectively inhibit tumor recurrence after photothermal treatment,showing significantly enhanced tumor treatment effect.This simple and multifunctional nanoagents is of great significance for imaging diagnosis before treatment and accurate treatment guided by NIR-?bioimaging.In this dissertation,we designed and synthesized organic fluorescent probes for different application scenarios according to their different photophysics and photochemistry.The NIR-? fluorescence probe was designed for high resolution fluorescence imaging in vivo by shifting the LUMO and HOMO.Concerning the deactivation process of triplet excited state by charge transfer,we introduced excited state quenchers into the molecular structure to enhance the photostability of the parent dyes.The heavy atom effect was used to increase the intersystem crossing process of BODIPY and then accelerated the energy transfer process between the triplet excited state of fluorescent molecule and molecular oxygen.Meanwhile,the singlet oxygen quantum yield was enhanced,which was beneficial to photodynamic therapy.The heat generated by internal conversion during deactivation process can be used for photothermal therapy.At the same time,an amphiphilic polypeptide carrier was used to regulate the circulation characteristics and distribution of dyes in the body,also to improve the biocompatibility of the probe. |
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