Iridium-Based Time-Resolved Luminescent Sensor for Ba²⁺ Detection

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 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 Ba²⁺-chelated compound is strongly enhanced. Furthermore, the residual phosphorescence emission of the free compound decays with two short decay constants, τ_free¹ ∼ 3.5 ns (88%) and τ_free² ∼ 209 ns (12%), while the chelated compound decays with two long decay constants, τ_bound¹ ∼ 429 ns (21%) and τ_bound² ∼ 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 Ba²⁺ tagging detector for neutrinoless double beta decay searches in xenon.