Complexing AIEE-active tetraphenylthiophene fluorophore to poly(N-isopropyl acrylamide): fluorescence responses toward acid, base and metal ions

Abstract

In this article, a multiple-responsive polymer micelles system was constructed by using an ionic bond as the link to connect the hydrophobic tetraphenylthiophene (TP) fluorophores having aggregation-induced emission enhancement (AIEE), and the hydrophilic poly(N-isopropyl acrylamide) (PNIPAM). The susceptibility of the ionic ammonium-sulfonate (Am-Sul) bond towards metal ions, acid and base triggered the AIEE-operative fluorescence (FL) response. To exercise the idea, PNIPAM with a sulfonate terminal was primarily prepared to react with an ammonium-functionalized TP derivative to generate a polymer complex of TP-PNIPAM. When in water, the polymer complex TP-PNIPAM formed micelles with the aggregated TP core interconnecting the hydrophilic PNIPAM shell by the ionic Am-Sul bonds. With the operative AIEE effect, the aggregated TP core in the micelles fluoresced strongly but upon the additions of metal ions, acid and base, the ionic bonds dissociated to result in the collapse of the micelles and the corresponding emission quenching. A novel fluorogenic sensor capable of responding to multi-stimuli was therefore constructed.