KINETICS OF PHOTOINDUCED ELECTRON-TRANSFER REACTIONS OF SOME ANTHRAQUINONE RADICAL-ANIONS WITH VARIOUS INORGANIC-IONS - COMPARISON WITH MARCUS CROSS-RELATION

The reactions of 2-, 2,6- and 2,7-anthraquinone (di) sulphonate radica l ions with the paramagnetic ions Fe(CN)(6)(3-), Cu2+, IrCl62- and Fe3 + have been studied at different pH-values at room temperature, in ord er 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 derivat ives the rate constants span over two orders of magnitude from 10(7) t o 10(9) mol(-1) dm(3) s (-1). The experimental rate constants have bee n compared with the predictions of the Marcus Cross-Relation, taking a lso into account the contribution of the diffusion pathway in our calc ulations. The predicted values are systematically larger than the expe rimental 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 theo ries has been stressed.