Coherent light sources can be used to manipulate the outcome of light-matte
r interactions by exploiting interference phenomena in the time and frequen
cy domain. A powerful tool in this emerging field of 'quantum control'(1-6)
is the adaptive shaping of femtosecond laser pulses(7-10), resulting, for
instance, in selective molecular excitation. The basis of this method is th
at the quantum system under investigation itself guides an automated search
, via iteration loops, for coherent light fields best suited for achieving
a control task designed by the experimenter(11). The method is therefore id
eal for the control of complex experiments(7,12-20). To date, all demonstra
tions of this technique on molecular systems have focused on controlling th
e outcome of photo-induced reactions in identical molecules, and little att
ention has been paid to selectively controlling mixtures of different molec
ules. Here we report simultaneous but selective multi-photon excitation of
two distinct electronically and structurally complex dye molecules in solut
ion. Despite the failure of single parameter variations (wavelength, intens
ity, or linear chirp control), adaptive femtosecond pulse shaping can revea
l complex laser fields to achieve chemically selective molecular excitation
. Furthermore, our results prove that phase coherences of the solute molecu
le persist for more than 100 fs in the solvent environment.