Excited-state proton-transfer dynamics between 7-hydroxy-4(trifluoromethyl)coumarin and 1-methylimidazole base in toluene were studied using ultrafast pump probe and time-resolved emission methods. Charge-transfer excitation of the hydroxycoumarin shifts electron density from the hydroxyl group to the carbonyl, resulting in an excited state where proton transfer to the base is highly favored. In addition to its the photoacid characteristics, the shift in the hydroxycoumarin electronic distribution gives it characteristics of a photobase as well. The result is a tautomerization process occurring on the picosecond time scale in which the 1-methylimidazole base acts as a proton-transfer shuttle from the hydroxyl group to the carbonyl.