Monophotonic Ionization of 7-Azaindole, Indole, and Their Derivatives and the Role of Overlapping Excited States

Abstract

<p>7-Azaindole undergoes monophotonic ionization just as its counterpart, indole. This result suggests that 7-azaindole is qualitatively more similar to indole than has previously been recognized. The appearance of the solvated electron for zwitterionic and anionic 7-azatryptophan and for 7-azaindole in water and methanol is complete within 1 ps, which indicates that the fluorescent state whose lifetime is >lo0 ps cannot be the source of the electron. The origin of the electron is related to the presence of closely spaced or overlapping excited states in 7-azaindole, which is another similarity that this chromophore bears with respect to indole. The fluorescence quantum yield of 7-azaindole is shown to be excitation wavelength dependent. The excitation-wavelength dependence and the temperaturedependence of the fluorescence quantum yield of 7-azaindole are explored and related to the production of the solvated electron. The implications of these observations for the use of 7-azatryptophan as an alternative to tryptophan as a probe of protein structure and dynamics are discussed.</p>