A luminescence probe for measurements of electron-exchange rates in polymer films on electrodes

The effect of metal ions on the, reduction of 1,10-phenanthroline-5,6-quinone (1), 5,8-quinolinequinone (II) and 6,7-dichloro-5, 8-quinolinequinone (III) has been investigated in 50% dimethylsulfoxide+water solvent. 1 contains the 1,10-phenanthroline structure in both its quinone and hydroquinone forms, while II and III contain the 8-hydroxyquinoline structure in the hydroquinone forms. Complexation of the hydroquinones of II and III by metal ions causes positive shifts in the quinone half-wave potentials. These shifts have been used to calculate conditional formation constants for Pb²⁺(II) and Pb²⁺ and Zn²⁺(III). The quinone form of I binds strongly to Ni²⁺, Co²⁺ and Zn²⁺ but not to Ca²⁺. Mg²⁺. Mg₂₊. Mn²⁺ and Pb²⁺. With the latter four metals, binding to the hydroquinone from of I was detected and formation constants were determined. In addition to binding both the quinone and hydroquinone forms at the nitrogen atoms, Ni₂₊ Co²⁺ and Zn²⁺ formed complexes at the 1,2-dihydroxy site of the hydroquinone of I.