The ultrafast dynamics of the internal conversion of S-1 azulene and the ex
cited-state intramolecular proton transfer in 2-(2'-hydroxyphenyl)benzothia
zole (HBT) were investigated by pump-probe spectroscopy with tunable pulses
as short as 20 fs. In both cases we find very pronounced oscillatory contr
ibutions to the transients, which are due to vibrational wavepacket motion
in the excited state. The damping times are on the order of I ps even for t
hese large reactive molecules in solution at room temperature. For azulene
only 2 out of 48 vibrational modes participate and in HBT only 4 out of 69.
This high degree of localization of the wavepacket seems to be a general f
eature, and supports hopes that even for systems of chemical interest coher
ent control might be possible.