Highly luminescent hydrogels synthesized by covalent grafting of lanthanide complexes onto PNIPAM via one-pot free radical polymerization

Abstract

Highly luminescent PNIPAM–Ln(DPA)₃ hydrogels have been synthesized by one-pot free radical polymerization in aqueous systems at room temperature. We firstly synthesized a bifunctional chelating ligand named as 4-vinylpyridine-2,6-dicarboxylic acid (4-VDPA), which contains two different moieties: (1) a pyridine-2,6-dicarboxylic acid (DPA) moiety that can sensitize the luminescence of Tb³⁺ and Eu³⁺ and (2) a reaction functional group that can be polymerized by free radical initiation. Therefore, the luminescent lanthanide complexes can be grafted onto the hydrogel matrix via one-pot free radical polymerization of [Ln(4-VDPA)₃]³⁻, N-isopropylacrylamide (NIPAM) and N,N′-methylenebis(2-propenamide) (MBA). The results indicated that the final hydrogels possess bright luminescence, long luminescence lifetimes and high quantum efficiency. Moreover, the emission colors of the hydrogels can be tuned from red, reddish orange, orange-yellow, yellow, and green by varying the molar ratio of added Eu³⁺ to Tb³⁺.