A New Time-resolved Luminescent Sensor

We present a new time-resolved chemosensor for the detection of Ba2+ ions. Our sensor is based on an iridium(III) compound with dual (fluorescent and phosphorescent) emission. The nature of the luminescent response of the sensor depends on its state; specifically, the phosphorescent emission of the free state at long wavelengths is strongly suppressed, while that of the Ba2+-chelated compound is strongly enhanced. Furthermore, the residual phosphorescent emission of the free compound decays with two short decay constants, τ 1 free ∼ 3.5 ns (88%) and τ 2 free ∼ 209 ns (12%), while the chelated compound decays with two long decay constants, τ 1ch ∼ 429 ns (21%) and τ 2 ch ∼ 1128 ns (76%). This exceptional behaviour, supported by quantum chemical calculations, allows a time- based separation between the signal of the free and the chelated species. Among other applications, our sensor could be the basis of a Ba2+ tagging detector for neutrinoless double beta decay searches in xenon.