Deuterium Isotope Effect on 4-Aminophthalimide in Neat Water and Reverse Micelles

Abstract

Picosecond time-resolved emission of 4-aminophthalimide (4-AP) in neat water and D 2 O 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 (φ f ) and lifetime (τ f ) of 4-AP is observed in neat D 2 O 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 D 2 O 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 D 2 O) slows down appreciably. The initial component of the solvation dynamics in reverse micelles, in the case of D 2 O, is observed to be 1.5 times slower than that in the case of H 2 O.