Studies On Phosphorescent Chemodosimeter For Hg²⁺ Based On Ir（Ⅲ） And Ru（Ⅱ） Complexes

Opto-chemical sensors have promising prospects in chemistry, biology, medicine and environmental studies. Recently, the use of phosphorescent heavy-metal complexes as chemosensors have attracted ever-increasing interest due to their rich variety structures and advantageous photophysical properties, such as larger Stokes shifts, long excited-state lifetimes, prominent color tunability, and suitable excitation in the visible region in comparison to most purely organic fluorophors. Although these phosphorescent chemosensors have shown potential and unique superiority, the further applications in time-resolved luminescence assay and biological imaging analysis are quite rare. On the other hand, the research on the design principles and sensing mechanisms of phosphorescent chemosensors is not enough and the related issues are remaining to be further deepened. Among metal ions, Hg²⁺ is considered to be one of the most hazardous species in nature. Therefore, it is worth looking forward to the development and application of novel phosphorescent chemosensors for recognization of Hg²⁺ in time-resolved photoluminescent analysis and bioimaging studies.This dissertation can be divided into six parts.Chapter 1: The research background and the design principles of phosphorescent chemosensors have been concisely reviewed. In particular, the development and application of phosphorescent chemosensors based on cyclometalated Ir（III） complex and Ru（II） polypyridyl complexes have been summarized.Chapter 2: We have rationally employed the “chemodosimeter approach” to develop a new phosphorescent probe P1 based on a cyclometalated Ir（III） complex, which utilizes an irreversible Hg²⁺-promoted desulfurization and cyclization reaction of the thiourea unit. The chemodosimeter exhibited a rapid turn-on phosphorescent response toward Hg²⁺ that was highly sensitive in aqueous media with a broad pH range 4-10. Furthermore, the chemodosimeter can be applied to monitor Hg²⁺ effectively by time-resolved luminescence detection and confocal luminescence imaging.Chapter 3: To get a better signal response, we attempted to develop the ratiometric phosphorescent chemodosimeter by changing the substitute position to give rise to sensitivity and selectivity. As expected, the chemodosimeter P3 displayed ratiometric luminescence change from yellowish-green to reddish-yellow only towards Hg²⁺ ions in aqueous media, which showed that the position of the substitution plays a decisive role in the emission wavelength tuning. The chemodosimeter was further used to time-resolved luminescence detection and live cell imaging.Chapter 4: Ru（II） polypyridyl complexes are another kind of important phosphorescent heavy-metal complexes. In this chapter, we developed a new phosphorescent probe P5 based on Ru（II） complex, which exhibited good water solubility, longer excitation wavelength and turn-on phosphorescent response only toward Hg²⁺ in aqueous system. Despite working as a reaction probe, P5 not only showed phosphorescent response quickly enough, but also had high sensitivity（less than 2.0 ppb） and stability within the pH range of 4–10. Through using time-resolved photoluminescence technique, P5 could eliminate effectively the signal interference from the short-lived fluorescent background in complicated media, accompanied with significant improvement of the signal-to-noise ratio and the accuracy of the detection for Hg²⁺. Furthermore, P5 with low cytotoxicity has been successfully used for bioimaging by using confocal laser scanning microscope, which may be favorable for biological applications to monitor and research effectively the bioaccumulation and bioavailability of Hg²⁺ in living cells.Chapter 5: We have develop another Ru（II） complex-based phosphorescent chemodosimeter P7 by changing the ancillary ligand. The chemodosimeter P7 exhibited an extremely low detection limit（1.1 ppb） and excellent phosphorescence enhancement response only to Hg²⁺ in water or HEPES buffer solutions. By using time-resolved luminescence assay, phosphorescent P7 could eliminate effectively the signal interference from the short-lived background fluorescent in complicated media and improve distinctly the signal-to-noise ratio of the detection. Furthermore, P7 with low cytotoxicity has been successfully used for bioimaging by using confocal laser scanning microscope, which may be favorable for biological applications to monitor and research effectively Hg²⁺ in living cells.In chapter 6, We systematically evaluated the design principles, structure–property relationships of phosphorescent chemodosimeter and their applications in time-resolved luminescence assay and biological imaging.