Synthesis and stability of BODIPY-based fluorescent polymer brushes at different pHs

Abstract

We report a simple strategy for the grafting of poly(methacrylic acid) [poly(MAA)] brushes from silicon substrate by surface-initiated RAFT polymerization and the subsequent coupling of BODIPY to these brushes to render them fluorescent. The poly(MAA) brushes were first generated by functionalization of hydrogen-terminated silicon substrate with methyl-10-undecenoate which both leads to the formation of an organic layer covalently linked to the surface via Sic bonds without detectable reaction of the carboxylate groups and couples to the polymerization initiator, followed by surface-initiated RAFT polymerization of tert-butyl methacrylate from these substrate-bound initiator centers, and finally conversion of tert-butyl groups to carboxylic acid groups. The poly(MAA) brushes were then made fluorescent by grafting a BODIPY derivative via an ester linkage. The stability of the BODIPY-based fluorescent polymer brushes in buffer solutions at pH 6.0 to 12.0 with added salt was investigated by ellipsometry, fluorescence microscopy, grazing angle-Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy. The results of these measurements indicated that the organic molecule-initiator bond (ester linkage) is unstable and can be hydrolyzed resulting in detaching of the immobilized polymer from the silicon substrate.