DEUTERIUM-ISOTOPE EFFECT ON 4-AMINOPHTHALIMIDE IN NEAT WATER AND REVERSE MICELLES

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 u ndergoes ultrafast solvent-mediated proton transfer and the emission o riginates 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-tr ansferred species. Nearly 4-fold increase in the emission quantum yiel d (phi(f)) and lifetime (tau(f)) of 4-AP is observed in neat D2O compa red 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 rev erse micelles the relaxation of the water (or D2O) slows down apprecia bly. The initial component of the solvation dynamics in reverse micell es, in the case of D2O, is observed to be 1.5 times slower than that i n the case of H2O.