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 B10 H10 (Et4 N)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. ϕP =0.48) among 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 , 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.
Keywords: carboranes; imaging agents; iridium; phosphorescence; structure-property relationships.
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