Rotationally resolved electronic spectroscopy of water clusters of 7-azaindole

The rotationally resolved electronic spectra of the electronic origin of the 7-azaindole-$(H2O)1$ and of the 7-azaindole-$(H2O)2$ clusters have been measured in a molecular beam. From the rotational constants the structures in the $S0$ and $S1$ electronic states were determined as cyclic with the pyrrolo NH and the pyridino N atoms being bridged by one and two water molecules, respectively. Excited state lifetimes of about $10ns$ for both clusters have been found. In the spectrum of the 7-azaindole-$(H2O)2$ cluster a splitting of the rovibronic band is observed, which can be traced back to a large amplitude motion, involving the out-of-plane hydrogen atoms of the water chain. Both the changes of the rotational constants upon electronic excitation and the orientation of the transition dipole point to a solvent induced state reversal between the $La$ and the $Lb$ states upon microsolvation.