Light-Emitting Redox Polymers for Sensing and Removal-Reduction of Cu(II): Roles of Hydrogen Bonding in Nonconventional Fluorescence

Here, intrinsically luminescent multifunctional n-butyl prop-2-enoate-co-butyl 3-(N-(hydroxymethyl)prop-2-enamido)propanoate-co-N-(hydroxymethyl)prop-2-enamide (NBP-co-BHMPP-co-HMP) luminogens with 1:2, 1:4, 1:8, and 1:20 mole ratios of NBP/HMP are synthesized via free radical polymerization, where the amidic BHMPP comonomer is anchored via N–C coupling of HMP and NBP. The optimum nonconventional fluorescent polymer (NCFP, NBP/HMP = 1:8) is suitable for sensitive detection, selective binding, and removal-reduction of Cu(II). The structures and light-emitting properties of NCFP, NCFP aggregates, Cu(II)-NCFP, and Cu(I)-NCFP; oxygen donor selective coordinations; and removal-reduction of paramagnetic Cu(II) are explored via spectroscopic, microscopic, density functional theory-reduced density gradient, rapid color change under visible light, chromaticity-1931 plots, and electrochemical measurements. The striking aggregation-enhanced green fluorescence is associated with extensive nonconventional and conventional hydrogen bondings in NCFP aggregates and through space electronic interactions involving NBP, HMP, and BHMPP moieties. Here, the Cu(II)/Cu(I) redox couple is confirmed via shifting of Epc from −1.08/+0.15 to +0.95/+0.16 V; Epc and Epa at +0.15 and −0.34/+0.41 V, respectively; green color of Cu(I)-NCFP under visible light; Fourier transform infrared and Cu 2p X-ray photoelectron spectroscopies; and computational studies. The limit of detection, Stern–Volmer constant, redox potentials, and adsorption capacity of NCFP are 3.61 nM/0.229 ppb, 4.27 × 103 [M]−1, and +0.15/+0.41/–0.34 V, and 49.41 mg g–1, respectively.