Synthesis of Biocompatible Aliphatic Terpolymers via In Situ Fluorescent Monomers for Three-in-One Applications: Polymerization of Hydrophobic Monomers in Water

Abstract

Biocompatible, nonconventional, multifunctional, purely aliphatic, light-emitting terpolymers, i.e., acrylonitrile-co-3-(N-isopropylacrylamido)propanenitrile-co-N-isopropylacrylamide (AN-co-NIPAMPN-co-NIPA, 1) and acrylonitrile-co-3-(N-hydroxymethylacrylamido)propanenitrile-co-N-hydroxymethylacrylamide (AN-co-NHMAMPN-co-NHMA, 2), were designed and synthesized via N–H-functionalized C–C + N–C-coupled in situ protrusions/grafting of fluorophore monomers, i.e., NIPAMPN and NHMAMPN, by solution polymerization of two highly hydrophobic nonemissive monomers in water. These scalable and reusable 1 and 2 were suitable for high-performance three-in-one applications, such as Fe(III) sensors, imaging of Madin–Darby canine kidney (MDCK) and human lung cancer (A549) cells, and security inks. The structures of 1 and 2, N–C-coupled in situ attachments/grafting of third fluorophore monomers, grafting events, and aggregation-enhanced emissions (AEEs), were analyzed by 1H and 13C NMR spectroscopy, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR) spectroscopy, ultraviolet–visible (UV–vis) spectroscopy, thermogravimetric (TG) analysis, high-resolution transmission electron microscopy (HRTEM), dynamic light scattering (DLS), fluorescence imaging, and fluorescence lifetime. The geometries, electronic structures, and absorption/emission properties of 1 and 2 at optimized compositions were examined by density functional theory (DFT), time-dependent DFT (TDDFT), and natural transition orbital (NTO) analyses. The limits of detection were 3.20 × 10–7 and 1.37 × 10–7 M for 1 and 2, respectively. The excellent biocompatibility of 1 and 2 was confirmed by >95% retention of MDCK and A549 cell morphologies.

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