ACID CATALYSIS OF EXCITED-STATE DOUBLE-PROTON TRANSFER IN 7-AZAINDOLE

The acid-catalyzed excited-state double-proton transfer (ESDPT) in 7-a zaindole has been studied. In carboxylic acids and phosphoric acids, t he formation of a 1:1 cyclic hydrogen bonded acid/7-azaindole complex was observed with a remarkably large association constant of >1.0 x 10 (4) M(-1). In contrast to alcohol-catalyzed ESDPT, in which the slow E SDPT dynamics involve a large amplitude of solvent reorganization, the rate of acid catalyzed ESDPT is much greater than the decay rate (sim ilar to 1.0 X 10(9) s(-1)) of the normal emission, resulting in a uniq ue tautomer emission. The highly efficient acid-catalyzed ESDPT in 7-a zaindole points to the biological application of 7-azaindole as a suit able acid derivative probe in a hydrophobic environment such as in the cell membrane.