Electron transfer reaction of 4,4'-bipyridine with triethylamine in acetonitrile: effect of water addition on the reaction dynamics

摘要

The photo-induced electron-transfer reaction of 4,4'-bipyridine (BPY) with triethylamine (TEA) in acetonitrile is studied by laser flash photolysis. The reaction mechanism and kinetics are found very sensitive to the presence of a small amount of water. At low water concentrations (i.e. <0.003 M), an extremely fast-rising metastable product is detected for the first time. A triplet charge transfer complex (~3ECT) is found to be the primary intermediate preceding the electron transfer process. Up to about 0.1 M, water facilitates the electron transfer rate, whereas higher water concentrations retard the rate of electron transfer. The Stern-Volmer plot of the triplet decay rate versus the TEA concentration is consistent with the presence of ~3ECT in equilibrium with the free excited triplet state of BPY.