Light-Emitting Redox Polymers for Sensing and Removal-Reduction of Cu(II): Roles of Hydrogen Bonding in Nonconventional Fluorescence
Joy Sankar Deb Roy, Mousumi Deb, MD Hussain Sanfui, Shrestha Roy, Arnab Dutta, Pijush Kanti Chattopadhyay, Narendra Nath Ghosh, Subhasis Roy, Nayan Ranjan Singha
Abstract
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.