ULTRAFAST ELECTRON-TRANSFER, RECOMBINATION AND SPIN DYNAMICS

The quenching of excited singlet methylene blue ((MB+)-M-1) by N,N-di methylaminomethylferrocene (FcN) in acetonitrile at room temperature h as been studied using femtosecond pump-probe absorption spectroscopy. At high FcN concentration static quenching via an intermolecular elect ron transfer mechanism constitutes the predominating decay channel for (MB+)-M-1 The time constants of the large amplitude components for t he forward electron transfer from FcN donor to (MB+)-M-1 and the subs equent recombination process recovering the ground states have been de termined to be 390 fs and 1 ps, respectively. Thus, the majority of ra dical pairs has recombined before paramagnetic relaxation induces spin mixing giving rise to triplet-phased radical pairs. These can escape geminate recombination as the system does not offer low-lying local tr iplet states to be occupied in the recombination process. (C) 1997 Els evier Science B.V.