A ruthenium-rhodamine complex as an activatable fluorescent probe.

We describe the synthesis and characterization of a ruthenium-bipyridyl complex bearing a rhodamine-based fluorescent ligand. The complex is weakly fluorescent due to the quenching of rhodamine. Upon irradiation of the MLCT band it releases rhodamine in a fast and clean heterolytic reaction, increasing its fluorescence nearly 6-fold and making it the first visible-light activatable fluorophore based in transition metal chemistry. These properties and its lack of toxicity make it a good candidate for its use as a biologically friendly caged fluorescent probe. The use of this probe as a neuronal marker, and as a flow profiler in a thin, planar cavity and in a model flow injection analysis (FIA) is demonstrated.