7-AZAINDOLE AND ITS CLUSTERS WITH AR, CH4, H2O, NH3, AND ALCOHOLS - MOLECULAR-GEOMETRY, CLUSTER GEOMETRY, AND NATURE OF THE 1ST EXCITED SINGLET ELECTRONIC STATE

Mass-resolved excitation vibronic spectra of jet-cooled 7-azaindole and its clusters with Ar, CH4, NH3, H2O, D2O, CH3OH, and C2H5OH are reported and analyzed with regard to molecular and cluster geometry and the nature of the first excited singlet state. Large changes in the various spectra are observed upon clustering and upon deuteration of 7-azaindole. The observed vibronic spectra of both 7-azaindole and its clusters can be rationalized with two general assumptions: (1) the hydrogen attached to the pyrrole nitrogen of 7-azaindole is out of the molecular plane in the first excited singlet state; and (2) the observed spectra are characterized by strong nπ*-ππ* mixing not completely removed by the clustering. MOPAC5 calculations of molecular geometry suggest that the S1 state is nonplanar. Additional cluster potential energy calculations suggest that the formation of cyclic hydrogen-bonded clusters is not likely for these gas-phase 1:1 or 1:2 7-azaindole/solvent clusters: the major gas-phase solvent clustering probably takes place at the π-system of the 7-azaindole molecule. © 1990 American Chemical Society.