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

Abstract

Quinoline photobases exhibit a distinctly higher p K a 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 p K a 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.

Traffic Lights for Catalysis: Stimuli‐Responsive Molecular and Extended Catalytic Systems

“…[54] For example, several studies concerning quinoline photobasicity have shown an increase in approximately 10 pK a units for quinoline derivatives exposed to UV light. [54,83] In particular, the excited states of the studied quinoline photobases are of sufficient energy to facilitate proton transfer from the reaction media (e.g., water or alcohols), which yields the conjugate base upon irradiation with an appropriate excitation wavelength (Figure 4b). The mechanism for generation of conjugate bases proceeds through abstraction of a proton from a hydrogen-bonded donor.…”

Ampeln für die Katalyse: Stimulus‐reaktive molekulare und erweiterte katalytische Systeme

“…[54] So haben beispielsweise mehrere Studien zur Photobasizität von Chinolin einen Anstieg des pK a -Wertes um circa 10 Einheiten bei Chinolinderivaten gezeigt, die UV-Licht ausgesetzt waren. [54,83] Insbesondere haben die angeregten Zustände der untersuchten Chinolin-Photobasen eine ausreichende Energie, um den Protonentransfer aus den Reaktionsmedien (z. B. Wasser oder Alkohole) zu erleichtern, wodurch bei Bestrahlung mit einer geeigneten Anregungswellenlänge die konjugierte Base entsteht (Abbildung 4b).…”

Can Brønsted Photobases Act as Lewis Photobases?

“…Separate experiments are needed to establish that a thermodynamically possible proton transfer process is also kinetically feasible. Previous work by us and others have demonstrated that quinolines are indeed kinetically competent for proton capture from a variety of proton donors. ,− The idea of Förster cycle analysis is, of course, general and has been employed to explain other excited-state processes before, including for metal–ligand interactions. , …”