TEMPERATURE EFFECTS ON RADICAL-ION AND TRIPLET QUANTUM YIELDS IN EXCITED-STATE ELECTRON-TRANSFER REACTIONS OF 1,12-BENZPERYLENE IN ACETONITRILE

Activation energies of 1,12-benzperylene fluorescence quenching (E-Q) in acetonitrile by a series of electron donors and accepters and of ra dical ion (E-R) and tripler state (E-T) formation were determined from Arrhenius plots of the quantum yields. The quenchers were chosen in t he range of Gibbs energies of electron transfer Delta G(et) = -100 to 6 kJ mol(-1) Surprisingly low E-Q, E-R and E-T values were obtained wh en Delta G(et) > -5 kJ mol(-1). The effects of temperature are discuss ed from the point of view of two alternative mechanisms: the conventio nal mechanism of direct electron transfer and that of transient excipl ex formation. Evidence for the latter is given. (C) 1998 Elsevier Scie nce B.V.