Bis(Naphthalimide-Piperazine)-Based Off-On Fluorescent Probe for Acids.

A bis(naphthalimide-piperazine) derivative (1) was synthesized as a pH-sensitive Off-On fluorescent probe. Operation mechanism of 1 is based on photo-induced electron transfer (PET) and its pH-dependent optical changes were investigated by using absorption and fluorescence spectroscopy. In the pH range of 11-4.5, this probe undergoes PET process from the piperazine to the naphthalimide moiety, leading to a fluorescence quenching. However, in the pH range of 4.5-1, the PET is inhibited to give a fluorescence enhancement. Moreover, the fluorescence 'turn-on' response of 1 is highly selective for protons (H(+)) over other metal cations, biomolecules and it shows a good reversibility between acidic and basic conditions. Graphical Abstract ᅟ.