Quinoline Photobasicity: Investigation within Water-Soluble Light-Responsive Copolymers

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.

Electroresponsive Polyelectrolyte Brushes Studied by Self-Consistent Field Theory

End-grafting of polyelectrolyte chains to conducting substrates offers an opportunity to fabricate electro-responsive surfaces capable of changing their physical/chemical properties (adhesion, wettability) in response to applied electrical voltage. We use a self-consistent field numerical approach to compare the equilibrium properties of tethered strong and weak (pH-sensitive) polyelectrolytes to applied electrical field in both salt-free and salt-containing solutions. We demonstrate that both strong and weak polyelectrolyte brushes exhibit segregation of polyions in two populations if the surface is oppositely charged with respect to the brush. This segregation gives rise to complex patterns in the dependence of the brush thickness on salt concentration. We demonstrate that adjustable ionization of weak polyelectrolytes weakens their conformational response in terms of the dependence of brush thickness on the amplitude of the applied voltage.

Block Copolymers Featuring Highly Photostable Photoacids Based on Vinylnaphthol: Synthesis and Self-Assembly

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 (MEO₉ MA/"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(O_m )-b-P(S_x -co-2VP_y -co-VN_z ), 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.