Kinetics of Photoinduced Electron Transfer Reactions of Some Anthraquinone Radical Anions with Various Inorganic Ions: Comparison with Marcus Cross-Relation

摘要

The reactions of 2-, 2,6- and 2,7-anthraquinone (di) sulphonate radical ions with the paramagnetic ions Fe(CN)_6~(3-), Cu~(2+), IrCl_6~(2-) and Fe~(3+) have been studied at different pH-values at room temperature, in order to investigate the role of spin states on electron transfer. With 2-anthraquinone sulphonate the rate constants are in the range 2.6-7 x 10~8 mol~(-1) dm~3 s~(-1), and for the other two anthraquinone derivatives the rate constants span over two orders of magnitude from 10~7 to 10~9 mol~(-1) dm~3 s~(-1). The experimental rate constants have been compared with the predictions of the Marcus Cross-Relation, taking also into account the contribution of the diffusion pathway in our calculations. The predicted values are systematically larger than the experimental values. This systematic deviation is justified in the present work as due to the spin-forbidden character of the reactions studied. The need for suited corrections in the current electron transfer theories has been stressed.