Spectroscopy of doubly hydrogen-bonded 7-azaindole. Reinvestigation of the excited state reaction

Luminescence of 7-azaindole (7AI) in non-polar solvents and alcohols was investigated with respect to its dependence upon temperature, concentration, and excitation energy. It was found that at low temperature oligomeric structures of 7AI are formed in the ground state. High-energy fluorescence (F₁) was shown to consist of dimeric and oligomeric contributions. The phosphorescence was assigned to oligomers. The mechanism of excited state cooperative double proton transfer is discussed along with the results of INDO/S calculations of transition energies and charge densities.