Using fluorine-containing amphiphilic random copolymers to manipulate the quantum yields of aggregation-induced emission fluorophores in aqueous solutions and the use of these polymers for fluorescent bioimaging

Abstract

Two new series of aggregation-induced emission (AIE) fluorophore-containing amphiphilic copolymers possessing the segments of a monomeric AIE fluorophore, N-(2-hydroxypropyl)methacrylamide (HPMA), [2-(methacryloyloxy)ethyl]trimethylammonium chloride (MATMA), and/or 2,2,2-trifluoroethyl methacrylate (TFEMA), were synthesized. Photophysical properties were investigated using UV-Vis absorbance and fluorescence spectrofluorometry. The increases of molar fractions of the hydrophobic AIE fluorophores and/or the trifluoroethyl moieties result in the higher quantum yields of the AIE fluorophores in the polymers. Using 1 mol% of AIE fluorophores with the tuning of molar fractions of TFEMA, 40% quantum yield was achieved, whereas only less than 10% quantum yield was obtained for the polymers without the TFEMA segments. The quantum yield difference indicates the importance of the fluorine segments for getting high quantum yields of the AIE fluorophores. These polymers were explored for fluorescent bioimaging using human brain glioblastoma U87MG and human esophagus premalignant CP-A cell lines. All the polymers are cell permeable and located in the cellular cytoplasm area. Cellular uptake was demonstrated to be through endocytosis, which is time and energy dependent. The polymers are non-cytotoxic to the two cell lines. Because the polymers contain ¹⁹F segments, we studied the spin–lattice relaxation time (T1) and spin–spin relaxation time (T2) of these polymers. T1 and T2 are the two important parameters for the evaluation of the capacity of these polymers for further applications in ¹⁹F magnetic resonance imaging (¹⁹F MRI). Structure influence on T1 and T2, especially on T2, was observed. These new multifunctional materials are the first series of fluorinated polymers with AIE fluorophores for bioapplications.