Ultrafast excited-state proton transfer and subsequent coherent skeletal motion of 2-(2 '-hydroxyphenyl)benzothiazole

The excited-state intramolecular proton transfer of 2-(2'-hydroxyphenyl)ben zothiazole was investigated with 30 fs temporal resolution. The proton take s 60 fs to arrive at its S-1 equilibrium position and the electron distribu tion changes on the same time scale. The molecule cannot adjust to the new structure of the H-chelate ring equally fast and starts to strongly vibrate in four low-frequency skeletal modes. This coherent wave packet motion is the cause of the experimentally observed strong signal oscillations that ar e only weakly damped despite the solvent environment. (C) 2000 American Ins titute of Physics. [S0021-9606(00)02424-7].