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

The green fluorescence (530 nm) of 7-azaindole tautomer is shown to be observable at room temperature upon microaddition of water (0.008 M to saturation) to ethyl ether and to p-dioxane (0. 1 7-1.7 M) as solvent. The fluorescence of 7-azaindole observed in liquid water solution (lambda(max) approximately 38 5 nm) is thus shown to correspond to the normal molecule (fluorescence at approximately 350 nm in ether), contrary to current proposals suggesting that this latter fluorescence corresponds to the tautomer. The present experiments indicate that 7-azaindole monohydrate undergoes excited-state double-proton transfer. The results also suggest that 7-azaindole polyhydrate, which is expected to be prevalent in water solvent, inhibits the solvent rearrangement that is necessary for tautomerization, resulting in a diminished tautomer fluorescence intensity.