Journal of the American Chemical Society, Vol.116, No.2, 735-746, 1994
Monophotonic Ionization of 7-Azaindole, Indole, and Their Derivatives and the Role of Overlapping Excited-States
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 >100 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 temperature dependence 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.
Keywords:EXPONENTIAL FLUORESCENCE DECAY;TRYPTOPHAN DERIVATIVES;ELECTRONIC SPECTROSCOPY;MAGNETIC-RESONANCE;HYDRATION DYNAMICS;QUANTUM YIELD;POLAR MEDIA;WATER;PHOTOPHYSICS;RESOLUTION