Does Excited-State Proton-Transfer Reaction Contribute to the Emission Behaviour of 4-Aminophthalimide in Aqueous Media?

作者：Khara Dinesh Chandra; Banerjee Sanghamitra; Samanta Anunay^*

来源：ChemPhysChem, 2014, 15(9): 1793-1798.

DOI：10.1002/cphc.201400078

• fluorescence spectroscopy
• hydrogen bonding
• isotope effects
• keto-enol transformations
• solvent effects

4-Aminophthalimide (AP) is an extensively used molecule both for fundamental studies and applications primarily due to its highly solvent-sensitive fluorescence properties. The fluorescence spectrum of AP in aqueous media was recently shown to be dependent on the excitation wavelength. A time-dependent blue shift of its emission spectrum is also reported. On the basis of these findings, the excited-state solvent-mediated proton-transfer reaction of the molecule, which was proposed once but discarded at a later stage, is reintroduced. We report on the fluorescence behaviour of AP and its imide-H protected derivative, N-BuAP, to prove that a solvent-assisted excited-state keto-enol transformation does not contribute to the steady-state and time-resolved emission behaviour of AP in aqueous media. Our results also reveal that the fluorescence of AP in aqueous media arises from two distinct hydrogenbonded species. The deuterium isotope effect on the fluorescence quantum yield and lifetime of AP, which was thought to be a reflection of the excited-state proton-transfer reaction in the system, is explained by considering the difference in the influence of H2O and D2O on the nonradiative rates and ground-state exchange of the proton with the solvent.

• 出版日期2014-6-23