Probing Solvation by Alcohols and Water with 7-Azaindole
The nonradiative pathways of 7-azaindole are extremely sensitive to solvent. In alcohols, 7-azaindole executes an excited-state double-proton transfer. In water, this tautomerization is frustrated. Proton inventory experiments suggest a concerted double-proton transfer in the alcohols and point to another nonradiative process in water. We propose the following idealized picture. Whereas at room temperature 7-azaindole can form a cyclic hydrogen-bonded intermediate with a single alcohol molecule facilitating tautomerization, in water more than one solvent molecule coordinates to the solute and thus prohibits the concerted process. More detailed measurements, however, indicate that water and alcohols do not solvate 7-azaindole in fundamentally different ways, but rather that they represent two extremes of the same phenomenon.
Reprinted (adapted) with permission from Structure and Reactivity in Aqueous Solution, ACS Symposium Series, Vol. 568, Chapter 13 (1994): 182, doi: 10.1021/bk-1994-0568.ch013. Copyright 1994 American Chemical Society.