Functionalized Bottlebrush Polymers as Bioinspired Photocatalysts for Highly Efficient Organic Transformations

Bioinspired catalysts replicate key catalytic functions of natural enzymes and offer innovative solutions to challenges in chemical synthesis, energy conversion, and environmental sustainability. In this study, bottlebrush polymers are synthesized via ring-opening metathesis polymerization (ROMP) and their use as bioinspired photocatalysts. By precisely controlling the degrees of polymerization, monomer composition and sequence, and the architecture of macromonomers, phenoxazine photosensitizer and/or bipyridine-nickel complexes are incorporated into bottlebrush polymers to afford photoredox and dual photocatalysts. Hydrophilic poly(ethylene glycol) macromonomers are copolymerized to impart water solubility, enabling efficient photocatalysis in aqueous media. The unique structural and topological features of the bottlebrush polymers significantly extended the excited-state lifetimes of photosensitizers and facilitated key photophysical processes, including electron, energy, and radical transfer processes. These features also govern the polymers' self-assembly in water, resulting in vesicular or spherical micellar structures that are topology-dependent and critically influence catalytic efficiency. Owing to these structural and assembly-driven advantages, the bottlebrush polymer catalysts outperformed their small-molecule and linear polymer counterparts in three photocatalytic organic transformations, namely benzimidazole synthesis, C_sp2-C_sp3 cross-couplings, and β-hydroxysulfonylation of α-methylstyrene in aqueous media. This work highlights the potential of functionalized bottlebrush polymers as highly efficient bioinspired photocatalysts for important organic transformations.