Deuterium isotope effect on the charge recombination dynamics of contact ion pairs formed by electron-transfer quenching in acetonitrile

The deuterium isotope effect on the fluorescence lifetime of contact ions p airs (CIP) composed of 9,10-dicyanoanthracene and weak aromatic electron do nors in acetonitrile has been investigated. For all pairs studied, an incre ase of the emission lifetime with increasing deuterium substitution on both the electron acceptor and the electron donor was observed. The free ion yi eld shows the same variation upon deuteration. It is concluded that the eff iciency of free ions formation is essentially determined by the competition , within the CIP, between charge recombination and dissociation into free i ons and that loose ion pairs do not play a significant role. (C) 2000 Elsev ier Science B.V. All rights reserved.