AN AB-INITIO STUDY OF ELECTRONIC-SPECTRA AND EXCITED-STATE PROPERTIESOF 7-AZAINDOLE IN VAPOR-PHASE AND AQUEOUS-SOLUTION

The geometries of 7-azaindole (7AI), its tautomer (7AT), and 7AI-H2O a nd 7AT-H2O complexes were optimised in the ground state and some low-l ying singlet excited states using the 3-21G basis set. Differences of total energies of the optimised ground and excited states and the vert ical excitation energies of these systems were used to explain the obs erved electronic spectra. Effect of solvation of these systems in bulk water was studied using the polarized continuum model (PCM). The mode of binding of a water molecule in the S-2(n-pi) excited state of 7AI was found to be quite different from those in its ground and pi-pi e xcited states. It is shown that crossing of the lowest two singlet exc ited-state potential surfaces S-1(pi-pi) and S-2(n-pi*) of 7AI occurs in the vapour phase under geometry relaxation while on interaction wi th water, the S-2(n-pi) excited state is raised up appreciably going even above the S-3(pi-pi) excited state. Ground-and excited-state mol ecular electrostatic potential mapping was carried out, which led to v aluable information regarding the nature of excited states of the abov e-mentioned systems. (C) 1998 Elsevier Science B.V. All rights reserve d.