Reversible photoactivation of 4-methylumbelliferone in carboxymethyl cellulose self-standing films under LED irradiation

Cellulose-derived materials capable of reversible optical responses are attractive for sustainable light-responsive technologies. Here, we demonstrate the reversible photoactivation of carboxymethyl cellulose (CMC) films containing 4-methylumbelliferone (4MU) under alternating UV-A/UV-C LED irradiation. The films show robust switching of absorbance through reversible 2+2 cycloaddition, maintaining performance over multiple cycles without fatigue. Molecular dynamics simulations reveal that CMC provides a highly connected free-volume network and strong 4MU–polymer interactions that promote efficient photodimerization, in contrast to cellulose acetate (CA), whose weaker supramolecular environment results in slower kinetics and reduced reversibility. Complementary thermal and AFM analyses confirm light-induced structural reorganization in CMC/4MU films, while a preliminary life cycle assessment highlights their lower environmental footprint. Overall, CMC/4MU emerges as a promising sustainable platform for reversible light-responsive materials.