Carboranes Tuning the Phosphorescence of Iridium Tetrazolate Complexes

New iridium tetrazolate complexes containing o-, m-, or p-carboranyl substitution in different positions of a phenylpyridine ligand have been prepared. The carborane isomers and the effect of their substitution position in the tuning of optical properties have been examined. The neutral complexes with the carboranyl substituent on the phenyl ring in meta position relative to the metal exhibit redshifted emission bands in contrast to blueshifts for those with carboranyl in para position. All cationic complexes display evidently blueshifted dual-peak emission compared with the carborane-free complex (c-TZ) with a broad single-peak emission. Introduction of carborane leads to a blueshift over 70nm relative to c-TZ. Carboranes also significantly improve phosphorescence efficiency (Φ_P) and lifetime (τ), that is, Φ_P=0.64 versus 0.21 (c-TZ) and τ=880ns versus 241ns (c-TZ). The unique hydrophilic nido-carborane-based Ir^III complex nido-o-1 shows the largest phosphorescence efficiency (abs Φ_P=0.57) among known water-soluble iridium complexes, long emission lifetime (τ=4.38μs), as well as varying emission efficiency and lifetime with O₂ content in aqueous solution. Therefore, nido-o-1 has been used as an excellent oxygen-sensitive phosphor for intracellular O₂ sensing and hypoxia imaging. Carboranes tuning phosphorescence: Carboranes can efficiently tune the photophysical properties of iridium complexes. nido-Carborane-based Ir^III complexes (see figure) are used as an oxygen-sensitive phosphor for intracellular O₂ sensing and hypoxia imaging.