<title>Responsive luminescent lanthanide complexes for sensing pH, pO<formula><inf><roman>2</roman></inf></formula>, and hydrogencarbonate in competitive aqueous media</title>

A series of chiral macrocyclic lanthanide complexes has been devised whose metal-based luminescence (Eu, Tb or Yb) is a function of a defined variable or set of variables. Complexes have been devised in which the lifetime or intensity of emission is a sensitive function of pH, pO₂, or halide ion concentration. The pH dependent systems report either the excited state singlet pK_a (Eu) or the triplet pK_a of an integral phenanthridinium chromophore, with luminescence enhancements of over 500. The halide and oxygen dependent systems operate differently via a quenching of the intermediate excited aryl singlet and triplet states respectively. In addition, complexes have been devised in which reversible binding of hydrogencarbonate displaces two bound water molecules, leading to an enhancement of the metal- based emission intensity (Eu, (Delta) J equals 2) or lifetime. At the same time, pronounced changes in the polarization of emission occur, signalling changes in the helicity at the metal center. Hydrogencarbonate chelates preferentially in the concentration range 20 to 40 mM in the presence of phosphate, lactate, citrate and halide at physiological levels.