Ratiometric oxygen sensors of cyclometalated iridium(iii) with enhanced quantum yields and variable dynamic ranges

Abstract

Four luminescent ratiometric oxygen sensors, pairing phosphorescent cyclometalated iridium with coumarin or BODIPY fluorophores, are presented here. These compounds realize three key improvements over our previous designs, namely higher phosphorescence quantum yields, the ability to access intermediate dynamic ranges better suited for typical atmospheric O₂ levels, and the possibility of using visible excitation instead of UV. These ratiometric sensors are accessed via very simple, 1-step syntheses involving direct reaction of the chloro-bridged cyclometalated iridium dimer with the pyridyl-substituted fluorophore. They have phosphorescent quantum yields up to 29% with short to intermediate phosphoresence lifetimes ranging from 1.7 to 5.3 μs in three of the sensors, with the fourth having a long lifetime of 440 μs that is very responsive to oxygen. In one case, visible excitation of 430 nm is used to provide dual emission instead of UV excitation.