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-<i>co</i>-3-(<i>N</i>-isopropylacrylamido)propanenitrile-<i>co</i>-<i>N</i>-isopropylacrylamide (AN-<i>co</i>-NIPAMPN-<i>co</i>-NIPA, <b>1</b>) and acrylonitrile-<i>co</i>-3-(<i>N</i>-hydroxymethylacrylamido)propanenitrile-<i>co</i>-<i>N</i>-hydroxymethylacrylamide (AN-<i>co</i>-NHMAMPN-<i>co</i>-NHMA, <b>2</b>), 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 <i>two</i> highly hydrophobic nonemissive monomers in water. These scalable and reusable <b>1</b> and <b>2</b> 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 <b>1</b> and <b>2</b>, N-C-coupled in situ attachments/grafting of <i>third</i> 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 <b>1</b> and <b>2</b> 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 <b>1</b> and <b>2</b>, respectively. The excellent biocompatibility of <b>1</b> and <b>2</b> was confirmed by >95% retention of MDCK and A549 cell morphologies.