Femtosecond charge transfer dynamics in artificial donor/acceptor systems:Switching from adiabatic to nonadiabatic regimes by small structural changes

The dynamics of intramolecular charge transfer (CT) in a family of conjugat ed aromatic electron donor/acceptor (D/ A) systems has been studied by femt osecond pump-probe spectroscopy. Although the compounds have very similar s tructures we observed vastly different CT dynamics, ranging from a few 100 fs to the nanosecond time range. These results show that specific modificat ions in the substitution scheme can lead to alterations of the relevant D/A orbitals and thus to drastic changes in the excited state electronic coupl ing. As a result the CT process switches from the ultrafast adiabatic to th e slow nonadiabatic regime. (C) 2001 Elsevier Science B.V. All rights reser ved.