Marcus inverted region: nature of donor–acceptor pairs and free ion yields

The free ion yield (ΦR) resulting from the fluorescence quenching of 9,10-dicyanoanthracene (DCA) by various electron donors in acetonitrile has been studied using ns laser photoconductivity. The influence of the chemical nature of the doors is established in a general manner. For a given oxidation potential Eox(D/D+), the rate constant of geminate ion recombination, kbac, decreases significantly as the electronic delocalization of the donor increases. As a consequence multiple Marcus plots are observed in the inverted region. These plots show decreasing curvature when going from stilbenes to amines as donors. This ‘fan effect’ is tentatively explained by considering the detailed roles of the parameters V, λ and hν in the Marcus model.