Contribution of the ultrafast, short-distance intermolecular electron transfer to the fluorescence quenching rate in solution

In a previous paper [S. Iwai , J. Chem. Phys. 112, 7111 (2000)] we have found ultrafast electron transfer (ET) which occurs between donor and acceptor molecules at short distances. We incorporate this ultrafast ET in the calculation of the second-order ET rate in order to explain the discrepancies between experimental [D. Rehm and A. Weller, Isr. J. Chem. 8, 259 (1970)] and theoretical [M. Tachiya and S. Murata, J. Phys. Chem. 96, 8441 (1992)] ET rates. The effect of the short-distance ET is significant in the Marcus normal region where the Marcus-type ET is not very fast. Compared to the case where the original Marcus equation is used as the first-order ET rate, the calculated second-order rate is found to increase by several orders of magnitude in the normal region. Thus the discrepancy between theory and experiment is potentially resolved and the importance of the short-distance ET in fluorescence quenching demonstrated. (C) 2001 American Institute of Physics.