Ultrabright Oxygen Optodes Based on Cyclometalated Iridium(III) Coumarin Complexes

Cyclometalated iridium(III) coumarin complexes represent new types of probes for optical oxygen sensing. In comparison to the most commonly used ruthenium(II) polypyridyl dyes and porphyrin complexes with platinum group metals, they possess much more efficient visible absorption and higher quantum yields, which results in much higher brightnesses. Spectral properties and oxygen sensitivity can be fine-tuned by varying the nature of the coumarin ligand and using respective monomeric or dimeric complexes. When incorporated in a model polystyrene film the probes show optimal dynamics of luminescence decay time for oxygen monitoring in the range from 0% to 100% air saturation. Cross-sensitivity to temperature is significantly lower than for the commonly used ruthenium(II)-tris-4,7-diphenyl-1,10-phenanthroline oxygen probe. The probes, however, exhibit significantly lower photostability, which restricts their application. If long-term measurements are not required, the probes can be successfully used for reliable monitoring of oxygen concentration. High brightness of the complexes makes them particularly attractive for application in thin films (for monitoring of fast processes) and various types of nano- and microparticles, including magnetic beads. If temperature compensation is not applied, the novel optodes result in the lower errors in determination of oxygen content.