Phosphorescent Hypochlorite Probes Based On Iridium(?) Complexes:Design,Preparation And Bioimaging Applications

Reactive oxygen species?ROS?play significant roles in varous physiological and pathological processes.It is reported that ROS can transmit cellular information,remove foreign materials and protect cells.Concentrated ROS,however,will destroy the antioxidant mechanism in living organisms,cause cell damages and even trigger apoptosis.Among various ROS,hypochlorite?ClO^-?is a research hotpot since it has strong oxidative properties,short lifetime and is also a hallmark of many diseases.Thus,it is important to design and develop highly sensitive and selective ClO^-probes to study ClO^--associated physiological processes.However,most ClO^-probes are based on small organic molecules,suffering from photobleaching,low quantum efficiency and strong background fluorescence in bioimaging.In order to solve these problems,in this study,we designed and synthesized two ClO^--sensitive probes based on long-lived phosphorescent iridium???complexes,namely dual-emission phosphorescent probe?Ir NPs?and near-infrared?NIR?phosphorescent probe Ir?btq?₂?bmn?.Then,we respectively employed ratiometric luminescence imaging,time-resolved photoluminescence imaging?TRPI?and NIR luminescence imaging to detect ClO^-in solutions and living cells,even in living mice bearing tumors?Ir NPs?with high signal-to-noise ratio?SNR?.These studies are shown as following.First,we designed a N^N ligand equipped with ClO^--responsive functional group to obtain ClO^--sensitive Ir?btq?₂?bmn?or Ir1 for short,and then we systematically investigated its detection mechanism via mass spectra,NMR,absorption and emission spectra.Subsequently,we introduced a ClO^--insensitive iridium???complex Ir2 as the reference through nanoprecipitation to construct a dual-emissive long-lived phosphorescent probe Ir NPs.During the detection of ClO^-,Ir NPs showed high emission quantum efficiency and photostbility.Importantly,ratiometric imaging is more accurate than intensity-based imaging due to the self-calibration of two channels,while TRPI can effectively distinguish long-lived phosphorescence of Ir NPs from short-lived background fluorescence,eliminating the interference from autofluorescence of living organisms.Ultilizing Ir NPs,we successfully detected ClO^-in solutions and cells through ratiometric luminescence imaging and TRPI.Specifically,we first confirmed the boosted ClO^-in elesclomol-stimulated tumors with high SNR using Ir NPs.Then,we selectively enlarged the conjugated skeleton of C^N ligand to reduce the energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital and to obtain a NIR long-lived ClO^--sensitive complex Ir?btq?₂?bmn?.We found that Ir?btq?₂?bmn?shows NIR emission?650-800 nm?,ClO^--responsiveness and good compatibility?cell penetrability and cytotoxicity?.Also,its long-wavelength excitation and NIR emission have competitive merits in the process of ClO^-detection since long-wavelength excitation has deeper tissue penetration and less photodamage,while little autofluorescence can be collected from NIR window,increasing the accurancy of ClO^-detection.Thus,through NIR luminescence imaging and TRPI,Ir?btq?₂?bmn?was employed to selectively monitor endogenous/exogenous ClO^-in the living cells with high SNR.