Mechanism of the quenching of the emission of substituted polypyridineruthenium(II) complexes by europium(II)

Abstract

The emission from the charge-transfer excited states of poly(pyridine)ruthenium(II) complexes (RuL/sub 3//sup 2 +/, L = a 2,2'-bipyridine or 1,10-phenanthroline derivative) is quenched by aqueous europium(II) at rate constants ranging from 1.5 x 10/sup 6/ to 1.0 x 10/sup 8/ M/sup -1/s/sup -1/(25/sup 0/C, 0.5 M ionic strength) depending on the identity of L. The quenching gives rise to the electron-transfer products RuL/sub 3//sup +/ and Eu(III) which undergo back-reaction to form RuL/sub 3//sup 2 +/ and Eu(II) at rate constants ranging from 2 to 6 x 10/sup 7/ M/sup -1/s/sup -1/. Energy-transfer and electron-transfer mechanisms are considered for the Eu(II) quenching process and the free energy dependences observed in europium outer-sphere electron-transfer reactions are reviewed. 4 figures, 3 tables.