Magneto-centric deep eutectic solvent-based photochromic hydrogels as light-induced smart rewritable materials

Light and magnetic responsive hydrogels, which demonstrate distinct responses by incorporating magnetic particles into photochromic hydrogels, have attracted considerable interest for their potential applications in smart optical devices. This study employs WO 3 nanocomposites, derived from magneto-centric deep eutectic solvents (DES), to modulate the magnetic and photochromic behavior of hydrogel system containing hydroxyethyl methacrylate (HEMA) and acrylamide (Am), i.e. p(HEMA/Am). The well-dispersed WO 3 nanocomposites in p(HEMA/Am)@WO 3 hydrogel lead to a 15-fold increase in its magnetization. Furthermore, the incorporation of the DES-based WO 3 nanocomposites enables a rapid photochromic response under UV-light irradiation, due to intermolecular charge transfer (ICT) between the WO 3 nanocomposites and the hydrogel matrix. Computational studies based on DFT calculations elucidate the charge transfer mechanism and validate the experimental results. The molecular orbital and the energy gap calculations confirm that WO 3 greatly improves electron transport in the hydrogel. The p(HEMA/Am)@WO 3 hydrogel exhibits excellent light-responsive, reversible pattern formation on its surface under UV irradiation, thereby evidencing its superior repeatability in writing and erasing information. The study highlights the significant contribution of DES-based nanocomposites in synthesizing photochromic hydrogels, underscoring their importance in advancing optical materials. Moreover, this research lays the foundation for designing photochromic materials for rewritable displays and information storage systems.