Fluorescent surface-grafted block copolymer brushes obtained in a versatile post-polymerization approach

Abstract

Surface-grafted luminescent polymer brushes are promising materials for applications in sensing, stimuli-responsive and light-harvesting systems.We report the synthesis of photoactive block copolymer brushes through surface-initiated atom transfer radical polymerization followed by post-polymerization functionalization and chain extension. The attachment of the bulky fluorophore, 6-aminofluorescein (6AF), to poly(glycidyl methacrylate) (poly(GMA)) brushes grafted from ITO-coated substrates was optimized by changing the solvent from DMSO to nitromethane and adjusting the amine catalyst from triethylamine to pentamethyldiethylenetriamine (PMDETA). This resulted in a faster, more controlled coupling of 6AF, leading to homogeneous distribution of chromophores within the brushes. Despite the aggregation-caused quenching nature of fluorescein, high concentrations of 6AF maintained efficient fluorescence, attributed to covalent attachment to polymer chains adopting extended conformations. Importantly, reducing PMDETA concentration preserved chain end activity, enabling the formation of a poly(GMA) block copolymer brush. The successful synthesis of block copolymers was confirmed by AFM and FTIR analyses. UV-Vis and fluorescence spectroscopy revealed that the formation of the second poly(GMA) block did not affect the photophysical properties of the first block. These photoactive block copolymer brushes, with densely packed, non-aggregated fluorophores, offer potential for light energy transfer applications and facilitate the fabrication of multi-block polymer systems with bulky pendant groups.