Luminescent lanthanide sensors for pH, pO₂ and selected anions

Stable lanthanide complexes have been devised in which the emission intensity or lifetime is a sensitive function of pH, pO₂ or halide concentration following excitation in the range 350-380 nm. The pH-dependent systems report the pK_a of the excited singlet or triplet of an integral phenanthridine chromophore. Modulation of the emission may occur via ligand or metal-centred processes: quenching of the singlet or triplet phenanthridine excited state occurs by halide and oxygen respectively; in complexes with chiral heptadentate ligands displacement of bound water molecules by lactate, phosphate and hydrogencarbonate leads to enhancements in the emission intensity and lifetime and pronounced changes in emission polarisation.