Deciphering Small Molecule Diffusion Parameters Across Light Responsive Polymersome Membranes

ABSTRACT Biological membranes orchestrate compartmentalization and selective transport to sustain out‐of‐equilibrium processes in living systems. Mimicking these dual roles with synthetic materials requires membranes that combine robustness with programmable permeability. Here, we report a systematic study of light‐responsive polymersomes in which Donor–Acceptor Stenhouse Adducts (DASAs) embedded in the hydrophobic leaflet act as photoswitchable regulators of molecular transport. A library of five amphiphilic block copolymers bearing increasing densities of DASA moieties was synthesized and self‐assembled into vesicular membranes. Using spectroscopic, calorimetric, and cryo‐EM techniques, we show that the degree of functionalization critically dictates both photoswitching efficiency and small‐molecule permeation. Importantly, polymersomes functionalized with ∼10% DASAs exhibited the highest light‐induced release rates, whereas higher densities reduced responsiveness due to light‐blocking effects, and reduced free volume for isomerization. This work provides a comparative framework for understanding how functional group density governs polymersome transport properties. By revealing design principles for balancing stability, responsiveness, and permeability, our findings establish guidelines for engineering stimuli‐responsive synthetic compartments as synthetic cells and nanoreactors with applications in biotechnology and therapeutics.