Syntheses And Cellular Imaging Applications Of Carborane-functionalized Novel Phosphorescent Iridium(Ⅲ)Complexes

Dicarba,closo-dodeccarboranes(carboranes,C2B10H12)are icosahedrons with twelve vertexes.They have very unique structures and special chemical properties,such as high thermal stability,geometrical symmetry,three-dimensional cage aromaticity,high boron content,good biological compatibility,and so on.Due to their intriguing natures,carboranes have been applied in a lot of areas,such as biological medicine,optical materials,catalysis,ionic liquid,and supramolecular chemistry.During the past decades,researches on icosahedral carboranes and its derivatives have achieved tremendous achievements.However,how to further expand the applications of carboranes,including taking advantage of their unique structures,has become great challenges of carborane chemistry.Some recent reports have incorporating carboranes into optical functional materials,in the forms of either carborane-based skeletons or carborane-modifing groups,to improve the performance of materials by using steric hindrances of the three-dimensional carborane cage-structures.Even so,the roles of carboranes on photophysical properties of optical functional molecules have not been addressed thoroughly,and many unique photophysical properties are still in the dark.Our group firstly introduced carborane isomers into classic phosphorescent iridium complexes and have obtained some new results when in biological imaging by using its unique properties and bioimaging techniques.This thesis aims to introduce the unique structures and electronic properties of carboranes into phosphorescent iridium complexes,which featuring tunable emission wavelength,high quantum efficiency,long lifetime,and high photostable ability,to develop multifunctional phosphorescent materials.The specific contents cover the following two parts:1.Studies on photophysical properties of carborane-functionalized iridium complexes and the intracellular hypoxia imagingThe structure-property relationship of carborane-modified iridium(Ⅲ)complexes has been investigated in this chapter.Firstly,an efficient synthetic approach for the new o-carborane-containing pyridine ligands(defined as a,b,c,d,e,and f)in high yields was developed by utilizing stable and cheap B10H10(Et4N)2 as the starting material.By using these ligands,novel iridium(Ⅲ)complexes Ⅰ-Ⅶ were efficiently prepared.In combination with DFT calculations,the photophysical and electrochemical properties of these complexes were studied.The hydrophilic nido-o-carborane based iridium(Ⅲ)complex Ⅷ showed the highest phosphorescence efficiency(abs.ΦP = 0.48)among the known water-soluble homoleptic cyclometalated iridium(Ⅲ)complexes and long emission lifetime(τ＝1.24 μs)in aqueous solution.Both of them are sensitive to O2,therefore endocellular hypoxia imaging of complex Ⅶ has been realized by the time-resolved luminescence imaging technology(TRLI).This is the first example to apply TRLI in endocellular oxygen detection with a water-soluble nido-carborane functionalized iridium(Ⅲ)complex.2.Studies on photophysical properties of carborane-based cationic iridium complexes and applications in monitoring mitochondrial polarityIn this chapter,a novel series of phosphorescent iridium(Ⅲ)complexes based on o-carborane functionalized N^N ligands have been designed and synthesized for the first time(2a-2e,3a-3e and 4).These complexes showed high emission quantum yields both in solution and in solid state(up to ΦPL=0.82),long emission lifetime and tunable emission wavelength over 74 nm by introduction of carboranyl motif in their ligands.Importantly,all the complexes have shown significant solvatochromic effects in contrast to the carborane-free control complex.Among them,complex 2d shows the highest sensitivity to polarity of solvents with a MPPS(maximum peak phosphorescence shift)value of 42 nm and evident dependence of phosphorescence lifetime on solvent polarity.Interestingly,complex 2d can easily penetrate into cells and preferentially distribute in mitochondria.To utilize these properties,the first phosphorescent imaging of mitochondrial polarity has been realized by photoluminescence lifetime imaging microscopy(PLIM),which can monitor mitochondria-relevant cellular processes such as cell apoptosis and to distinguish cancer cells from normal cells.Compared to intensity-based sensing,lifetime-based detection is independent of the probe concentration,excitation power and photobleaching of probes,which can show high accuracy and reproducibility.