Femtochemistry of hydrogen bonded complexes after electronic excitation in the liquid phase: The case of coumarin 102

We review our results on hydrogen bonding dynamics in the electronically excited state of coumarin 102 (C102), where we deduced that a hydrogen bond cleavage occurs within 200 fs. We compare the electronic absorption and emission properties of C102 hydrogen bonded to CHCl3, phenol or 2,2-dimethyl-3-ethyl-3-pentanol. We introduce the technique of two-pulse photon echo to show that an optical coherence between the optically coupled electronic ground and excited states survives until 180-200. fs, in the case of C102(phenol)(1,2) complexes, and argue that this is an indication that an electronic state hopping occurs around this time. By comparison with the previous pump-probe and grating scattering results we deduce that this state hopping is accompanied by a hydrogen bond cleavage.