Eu(3+)- and Tb(3+)-Based Coordination Complexes of Poly(N-Isopropyl,N-methylacrylamide-stat-N,N-dimethylacrylamide) Copolymer: Synthesis, Characterization and Property

This contribution reports the syntheses, structural analyses and properties of europium (Eu(3+))- and terbium (Tb(3+))-based coordination complexes of poly(N-isopropyl,N-methylacrylamide-stat-N,N-dimethylacrylamide) (poly(iPMAm-stat-DMAm)) copolymer, named as poly-Eu(III) and poly-Tb(III), respectively. In greater detail, poly(iPMAm(85)-stat-DMAm(15)) is first prepared by random copolymerization of N-isopropyl,N-methylacrylamide (iPMAm) and N,N-dimethylacrylamide (DMAm) via group transfer polymerization (GTP). Next, poly(iPMAm(85)-stat-DMAm(15)) is used as the polymer matrix for chelating with Eu(3+) and Tb(3+) cations at its side amide groups, to produce poly-Eu(III) and poly-Tb(III). Their structural characterizations by FT-IR spectroscopy and XPS confirm the formation of polymeric complexes. The study on their fluorescence emission characteristics and luminescence lifetime demonstrates that Poly-Eu(III) shows four strong emission peaks at 578, 593, 622, and 651 nm, which are responsible for the electron transitions from the excited (5)D(0) state to the multiplet (7)F(J) (J = 0, 1, 2, 3) states, respectively, and poly-Tb(III) also displays four emission peaks at 489, 545, 588, and 654 nm, mainly due to the electron transitions of (5)D(4) → (7)F(i) (i = 6, 5, 4, 3). The luminescence lifetimes of poly-Eu(III) (τ(poly-Eu(III))) and poly-Tb(III) (τ(poly-Tb(III))) are determined to be 4.57 and 7.50 ms, respectively. In addition, in aqueous solutions, poly-Eu(III) and poly-Tb(III) are found to exhibit thermoresponsivity, with their cloud temperatures (T(c)s) locating around 36.4 and 36.8 °C, respectively. Finally, the cytotoxicity study on the human colon carcinoma cells LoVo and DLD1 suggests that the luminescent Eu(3+) and Tb(3+) in the chelated state with poly(iPMAm-stat-DMAm) show much better biocompatibility and lower toxicity than their inorganic salts.