Light-controlled, living radical polymerisation mediated by fluorophore-conjugated RAFT agents

Abstract

Photoinduced electron transfer-reversible addition−fragmentation chain-transfer (PET-RAFT) polymerisation allows the controlled synthesis of polymers and provides an alternative to transition metal-based photoinitiators. Here, fluorophore-conjugated RAFT agents, containing either 5-carboxyfluorescein or a “boron-dipyrromethene” (BODIPY) moiety attached to a thiocarbonylthio group, were synthesised. Both agents enabled light-controlled (470 nm, 0.4 mW/cm2) “on/off” polymerisation yielding polymers with a Mw/Mn < 1.50. The BODIPY-based RAFT agent showed excellent photostability and gave polymers that contained a single fluorophore per polymer chain, providing an expedient route to homogeneous fluorescently labelled polymers. This agent was compatible with multiple acrylamide/acrylate monomers with a range of functional groups, with the thiocarbonylthio terminating group enabling further polymer chain extension and the formation of fluorescent block copolymers, as demonstrated by the synthesis of BODIPY-labelled poly(N,N-dimethylacrylamide)-block-poly (3-acrylamidophenyl)boronic acid).