Photochemistry in Confined Environments for Single-Chain Nanoparticle Design

Abstract

Emulating nature's protein paradigm, single-chain nanoparticles (SCNP) are an emerging class of nanomaterials. Synthetic access to SCNPs is limited by ultralow concentrations, demanding reaction conditions, and complex isolation procedures after single-chain collapse. Herein, we exploit the visible light photodimerization of styrylpyrene units as chain folding mechanism. Critically, their positioning along the polymer chain creates a confined environment, increasing the photocycloaddition quantum yields dramatically, enabling single-chain folding at unrivaled high concentrations without subsequent purification. Importantly, the enhanced photoreactivity allows for single-chain folding at λ = 445 nm LED-irradiation within minutes as well as via ambient light, enabling an unprecedented folding system. The herein demonstrated enhancement of quantum yields by steric confinement serves as a blueprint for all photochemical ligation systems.

Making and Breaking Chemical Bonds by Chemiluminescence

“…As illustrated in Figure , within the first 30 min of irradiation, a conversion of close to 30% was observed. In agreement with our earlier findings, the apparent quantum yield of the cycloaddition decreases over the course of the reaction, leading to a decrease of conversion with each additional irradiation step. After 11 h of reaction time (including dark periods), more than 60% of the styrylpyrene units were dimerized.…”

Macromolecular Superstructures: A Future Beyond Single Chain Nanoparticles

“…If an excited molecule does not find a suitable reaction partner within the lifetime of its excited state, the molecule is deactivated and not reactive anymore. Consequently, the quantum yield (ϕ) of the photoreaction is diffusion and concentration dependent – and occurs only above a certain concentration threshold (Figure , bottom left) . Since the concentration of photoreactive units within the polymer coil is higher than the global concentration of photoreactive units in the reaction vessel, the quantum yield of the intramolecular reaction is significantly higher than for intermolecular pathway.…”

“…Using the [2+2] photocycloaddition chemistry of a stilbene derivative, styrylpyrene, we have recently reported a quantum yield of ϕ=0.07 for the intrachain dimerization of a polymer containing 28 % of pendant reactive units . When the same photoreactive molecule was investigated in free solution, without macromolecular confinement at the same overall concentration (0.7 mM), the quantum yield was observed to be close to zero and no reaction could be detected.…”

All Eyes on Visible‐Light Peroxyoxalate Chemiluminescence Read‐Out Systems

“…Various mechanisms for the PO‐CL have been proposed in the past 50 years since its discovery and numerous experiments have been conducted to confirm suggested mechanisms and their intermediates. Our group has recently demonstrated the effect of confined environments, which polymers provide, on photochemical single chain nanoparticle folding . Similarly, a copolymer consisting of two blocks bearing different fluorophores with distinct emission spectra could provide such a confined environment.…”