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 10 ns 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.