Solid fluorescence sensors obtained by functionalization of photocrosslinked water-swollen acrylic membranes with 4-piperazine naphthalimide derivatives

Abstract

A photocrosslinked membrane (M-Cl) based on vinyl-pyrrolidone/butyl acrylate containing ethylene glycol dimethacrylate as a crosslinking agent and methacryloyl chloride as reactive monomer has been prepared for further functionalization. A series of hydroxy substituted piperazine naphthalimide compounds have been synthetized as pH sensitive Off-On fluorescence probes using two methods: microwave and reflux. Three of the derivatives were selected to be anchored to the M-Cl membrane through the acid chloride groups by the Schotten-Baumann reaction. All the obtained water-swollen membranes were characterized using different techniques. Photo-induced electron transfer (PET) and its pH-dependent optical changes were investigated and various photochemical parameters were determined by using pH-dependent absorption and fluorescence spectroscopies. In the pH range of 9.0–4.0, these solid sensors undergo PET process from the piperazine to the naphthalimide moiety leading to a fluorescence quenching. However, in the pH range of 4.0–1.0, the PET is inhibited to give a fluorescence enhancement. The sensitivity of the functionalized membranes to pH changes depended on the size and position of the naphthalimide substituents.