Polymeric Photoacids based on Naphthols – Design Criteria, Photostability, and Light-Mediated Release

The implementation of photoswitches within polymers offers an exciting toolbox in the design of light-responsive materials. We introduce a range of water-soluble copolymers featuring naphthol-based chromophores as photoacids and the resulting materials experience a drastic increase in acidity upon stimulation with UV light. We systematically studied how structure and distance of the photoacid from the copolymer backbone determines polymerizability, photo-response, and photostability. Briefly, we used RAFT polymerization to prepare copolymers consisting of nona(ethylene glycol) methyl ether methacrylate (MEO 9 MA) as water-soluble comonomer in combination with six different 1-naphthol-based (“N”) monomers. Thereby, we distinguish between methacrylates (NMA, NOeMA), methacrylamides (NMAm, NOeMAm), vinyl naphthol (VN), and post-polymerization modification based on (1-hydroxynaphthalen-2-amido)ethyl)amine (NOeMAm, NAmeMAm). After synthesis and characterization via NMR spectroscopy and size exclusion chromatography (SEC), we investigated how potential photo-cleavage or photo-degradation during irradiation depends on type and distance of linker to the copolymeric backbone and whether reversible excited state proton transfer (ESPT) occurs under these conditions. In our opinion, such materials will be strong assets light-mediated proton sources in nanostructured environments, e.g. for the site-specific creation of proton gradients.