Cellulose nanocrystal gels as radical reservoirs

Abstract

Gels that sustain reactive radical species under aerobic ambient conditions remain rare, limiting the development of soft materials that exploit redox-active chemistry. Here, we show that cellulose nanocrystal (CNC) gels containing a deep eutectic solvent (DES) create an oxygen-resistant environment that supports the photochemical and electrochemical generation of long-lived viologen radicals. The DES medium drives gel formation and produces mechanically strong networks in which viologen radical formation is fully reversible and coupled to optical and mechanical responses. These gels function as redox-responsive media for information storage, enabling photoactive and electroactive coatings with spatial and temporal control over message development. Extending the platform to a tetracationic viologen macrocycle shows that radical–radical host–guest complexes can form and dissociate within the gel matrix, giving rise to an optical response distinct from those of the individual radicals. These results establish DES-containing CNC gels as a versatile platform for stabilizing and manipulating radical species in soft materials, opening new avenues to aerobic electrochromic devices, UV-responsive systems, and in-gel supramolecular redox chemistry.