Iridium-Based Time-Resolved Luminescent Sensor for Ba Detection.

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