Structure and tautomerism of 7-azaindole in the ground and excited states

Ab initio calculations of the tautomers of the monomer and the dimer of 7-azaindole in the ground and excited states are reported, using the 3-21G and 6-31G* basis sets. The obtained results for the transition energies are compared with spectroscopic measurements. The CIS frozen-core method used to study the excited states adequately predicts the shape of the curves but it fails to predict the excitation energies. Also, CIS(D) calculations were performed in order to improve the CIS excitation energies. The asymmetry of the curves and the large barriers for the monomer at the ground and excited states do not allow the proton transfer. For the dimer the barriers are still large but the symmetry of the curve in the two excited states studied could allow the proton transfer by tunneling. (C) 1999 Elsevier Science B.V. All rights reserved.