Ultrafast structural response of hydrogen bonded complexes to electronic excitation in the liquid phase

The response of hydrogen bonded complexes to electronic excitation is studied by site-specific vibrational spectroscopy in the femtosecond domain, providing insight into local changes of hydrogen bonding geometries. For the prototypical organic complex coumarin 102-(phenol)(1,2) in solution, electronic excitation of the coumarin chromophore initiates a response of intermolecular hydrogen bonds on two distinct time scales: the hydrogen donor (phenol)(1,2) is released from the acceptor coumarin within 200 fs, followed by a reorganization of the (phenol)a moiety with an 800 fs time constant. This structural response results in strong changes of vibrational dipole moments which are monitored for the first time.