FEMTOSECOND INTERMOLECULAR ELECTRON-TRANSFER IN CONDENSED SYSTEMS

We have investigated the ultrafast intermolecular electron transfer (E T) from an electron-donating solvent (aniline (AN) or N,N-dimethylanil ine (DMA)) to an excited dye molecule (oxazines (Nile blue and oxazine 1) or coumarins). A non-exponential time dependence was observed in A N and can be explained by solvent reorientation and nuclear motion of the reactants. However, in DMA, a single exponential process was obser ved for Nile blue (160 fs) and oxazine 1 (280 fs), which can be explai ned by assuming that the rate of ET is limited mainly by ultrafast nuc lear motion. A clear substituent effect on intermolecular ET was obser ved for the 7-aminocoumarins. When the alkyl chain on the 7-amino grou p is extended and a hexagonal ring with the benzene moiety is formed, the rate of ET is reduced by three orders of magnitude. This effect ca n be explained by a change in the free energy difference of the reacti on and by the vibrational motion of the amino group.