Picosecond time-resolved emission of 4-aminophthalimide (4-AP) in neat water and D2O and in the water pool of aerosol OT reverse micelles in n-heptane is reported. It is proposed that in protic solvents’ 4-AP undergoes ultrafast solvent-mediated proton transfer and the emission originates from the proton-transferred species. The abrupt decrease in the emission quantum yield and lifetime of 4-AP in protic solvents is attributed to the reduction in the S-1-S-0 energy gap in the proton-transferred species. Nearly 4-fold increase in the emission quantum yield (phi(f)) and lifetime (tau(f)) of 4-AP is observed in neat D2O compared to water. This is ascribed to the retardation of the nonradiative S-1 --> S-0 internal conversion processes on deuteration of the imide proton. In neat water or D2O the solvation dynamics is too fast to be detected using our picosecond setup. However, in the water pool of reverse micelles the relaxation of the water (or D2O) slows down appreciably. The initial component of the solvation dynamics in reverse micelles, in the case of D2O, is observed to be 1.5 times slower than that in the case of H2O.