A Convenient Approach To Synthesize o-Carborane-Functionalized Phosphorescent Iridium(III) Complexes for Endocellular Hypoxia Imaging

The structure-property relationship of carborane-modified iridium(III) complexes was investigated. Firstly, an efficient approach for the synthesis of o-carborane-containing pyridine ligands a-f in high yields was developed by utilizing stable and cheap B10H10(Et4N)(2) as the starting material. By using these ligands, 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 VII showed the highest phosphorescence efficiency (abs. phi P =0.48) among known water-soluble homoleptic cyclometalated iridium(III) complexes and long emission lifetime (=1.24s) in aqueous solution. Both of them are sensitive to O-2, and thus endocellular hypoxia imaging of complex VII was realized by time-resolved luminescence imaging (TRLI). This is the first example of applying TRLI in endocellular oxygen detection with a water-soluble nido-carborane functionalized iridium(III) complex.