Aggregation induced emission (AIE) active cross-linked poly(N-isopropyl acrylamide-co-tetra(phenyl)ethene di-acrylates): sensors for effective nitroaromatics detection in an aqueous environment

Aggregation induced emission (AIE) active cross-linked copolymers CP1-4 with high molecular weights (12 700-14 100) and low polydispersity indices (1.2-1.3) were prepared through copolymerization of N-isopropyl acrylamide (NIPAM) and tetra(phenyl)ethene (TPE)-based acrylate dimers. CP1-4 show comparable thermal stability to poly(N-isopropylacrylamide) (PNIPAM), while their glass transition temperatures are higher by 11-13 °C than that of pristine PNIPAM. CP1-4 are soluble in common organic solvents and water. They are thermally sensitive like PNIPAM, with reduced lower critical solution temperatures (LCSTs) associated with higher TPE content. CP1-4 show typical AIE properties, which are similar to those of reported linear copolymers LP1-4. The fluorescence of CP1-4 in pure water could be significantly quenched by a wide range of nitroaromatics, including picric acid (PA), 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (DNT) and 4-nitrotoluene (NT). Nevertheless, the detection sensitivity of CP1-4 could be greatly improved through a collapsing-swelling process, in which the formation and interaction of non-covalent bonding between TPE groups and nitroaromatic molecules are significantly enhanced, resulting in reduced detection levels as low as 0.25 μg mL⁻¹ or 0.25 ppm. Thus, CP1-4 has the potential for highly sensitive detection of a variety of nitroaromatics in aqueous environments.