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Author: Dietzek, Benjamin × Author: Sittig, Maria × Publisher: Weinheim : Wiley-VCH ×

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    Block Copolymers Featuring Highly Photostable Photoacids Based on Vinylnaphthol: Synthesis and Self-Assembly
    (Weinheim : Wiley-VCH, 2020) Wendler, Felix; Tom, Jessica C.; Sittig, Maria; Biehl, Philip; Dietzek, Benjamin; Schacher, Felix H.
    The synthesis of a photoresponsive amphiphilic diblock quarterpolymer containing 5-vinyl-1-naphthol (VN) as a photostable photoacidic comonomer is presented. The preparation is realized via a sequential reversible addition fragmentation chain transfer (RAFT) polymerization starting from a nona(ethylene glycol) methyl ether methacrylate (MEO9MA/“O”) hydrophilic block, which is then used as a macro-RAFT agent in the terpolymerization of styrene (S), 2-vinylpyridine (2VP), and TBS-protected VN (tVN). The terpolymerization proceeds in a controlled fashion and two diblock quarterpolymers, P(Om)-b-P(Sx-co-2VPy-co-VNz), with varying functional comonomer compositions are prepared. These diblock quarterpolymers form spherical core-corona micelles in aqueous media according to dynamic light scattering (DLS) and cryogenic transmission electron microscopy (cryo-TEM). Upon irradiation, the photoacids within the micellar core experience a drastic increase in acidity causing a proton transfer from the photoacid to neighboring 2VP units. As a result, the hydrophilic/hydrophobic balance of the entire assembly is shifted, and the encapsulated cargo is released. © 2020 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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    Quinoline Photobasicity: Investigation within Water-Soluble Light-Responsive Copolymers
    (Weinheim : Wiley-VCH, 2021) Sittig, Maria; Tom, Jessica C.; Elter, Johanna K.; Schacher, Felix H.; Dietzek, Benjamin
    Quinoline photobases exhibit a distinctly higher pKa in their electronically excited state than in the ground state, thereby enabling light-controlled proton transfer reactions, for example, in molecular catalysis. The absorption of UV light translates to a pKa jump of approximately 10 units, as established for small-molecule photobases. This contribution presents the first synthesis of quinoline-based polymeric photobases prepared by reversible addition-fragmentation chain-transfer (RAFT) polymerization. The integration of quinolines as photobase chromophores within copolymers offers new possibilities for light-triggered proton transfer in nanostructured materials, that is, in nanoparticles, at surfaces, membranes and interfaces. To exploit the light-triggered reactivity of photobases within such materials, we first investigated how the ground- and excited-state properties of the quinoline unit changes upon polymer integration. To address this matter, we combined absorption and emission spectroscopy with time-resolved transient-absorption studies to reveal photoinduced proton-transfer dynamics in various solvents. The results yield important insights into the thermodynamic and kinetic properties of these polymeric quinoline photobases. © 2020 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH
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    Polymeric Photoacids Based on Naphthols—Design Criteria, Photostability, and Light-Mediated Release
    (Weinheim : Wiley-VCH, 2019) Wendler, Felix; Sittig, Maria; Tom, Jessica C.; Dietzek, Benjamin; Schacher, Felix H.
    The implementation of photoswitches within polymers offers an exciting toolbox in the design of light-responsive materials as irradiation can be controlled both spatially and temporally. Herein, we introduce a range of water-soluble copolymers featuring naphthol-based chromophores as photoacids in the side chain. With that, the resulting materials experience a drastic increase in acidity upon stimulation with UV light and we systematically studied how structure and distance of the photoacid from the copolymer backbone determines polymerizability, photo-response, and photostability. Briefly, we used RAFT (reversible addition–fragmentation chain transfer) polymerization to prepare copolymers consisting of nona(ethylene glycol) methyl ether methacrylate (MEO9MA) 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). These P(MEO9MAx-co-“N”y) copolymers typically feature a 4:1 MEO9MA to “N” ratio and molar masses in the range of 10 kg mol−1. After synthesis and characterization by using NMR spectroscopy and size exclusion chromatography (SEC), we investigated how potential photo-cleavage or photo-degradation during irradiation depends on the type and distance of the 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 as light-mediated proton sources in nanostructured environments, for example, for the site-specific creation of proton gradients. We therefore exemplarily incorporated NMA into an amphiphilic block copolymer and could demonstrate the light-mediated release of Nile red from micelles formed in water as selective solvent. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.