Photoactive graft amphiphilic polyelectrolyte: Facile synthesis, intramolecular aggregation and photosensitizing activity

Abstract

Simple and versatile two-step procedure for synthesis of graft amphiphilic polyelectrolytes has been developed. A photoactive copolymer of poly(vinylnaphthalene) grafted from poly(sodium 2-acrylamido-2-methyl-1-propanesulfonate) (PAMPS-graft-PVN) was obtained and characterized. By separating the processes of generation of grafting sites on the precursor main chain and subsequent nitroxide-mediated polymerization (NMP), the formation of the unwanted homopolymer could be avoided. Combination of charged polymer backbone with short hydrophobic side chains in PAMPS-graft-PVN leads to spontaneous intramolecular aggregation of the macromolecule in an aqueous solution with formation of hydrophobic domains consisting of highly packed naphthalene chromophores arranged in a “pearl-necklace” structure as shown using atomic force microscopy. The presence of fluorophores in the polymer structure is beneficial for the studies of such macromolecular system as it allows application of emission spectroscopy, which is very sensitive to structural arrangement of the fluorophores. The domains formed within the polymer chain in an aqueous solution were also characterized using fluorescent molecular probes. Studies on photophysical properties of PAMPS-graft-PVN indicated that the polymer can be an efficient photosensitizer in photoinduced electron transfer processes. The proposed here synthetic approach can be easily applied for syntheses of other graft copolymers that are otherwise difficult to be obtained.