KINETIC PARAMETERS FOR A SYSTEM AT EQUILIBRIUM FROM THE TIME COURSE OF LUMINESCENCE EMISSION: A NEW PROBE OF EQUILIBRIUM DYNAMICS. EXCITED-STATE EUROPIUM(III) AS A SPECIES LABEL.

Article abstract of DOI:10.1021/ja00349a013

Forward and reverse rate constants for the equilibrium between the europium(III) complex of 1,2-diaminocyclohexanetetraacetate, Eu(DCTA)** minus , and iminodiacetate, IMDA**2** minus , to form the ternary complex Eu( left brace DCTA)(IMDA)**3** minus are obtained from the time course of luminescence emission following selective laser excitation of the Eu(III)-containing species. This new method depends upon selective excitation of the **7F//0 yields **5D//0 electronic transition of a particular Eu(III) species while monitoring the time course of luminescence emission, either predominately from the same species or from one into which it is converted chemically, at a rate comparable to the reciprocal lifetime of the excited state of the species involved. Since excited state Eu(III) has the same reactivity in ligand-exchange reactions as the ground-state ion, the electronic excitation acts as a species label in a manner analogous to the use of nuclear spin saturation transfer as a nuclear label. Twelve different luminescence emission curves obtained at three different pH values (four permutations of lambda //e//x and lambda //e//m at each pH)) were fit with a total of five adjustable parameters.