Enhancing Photochromism of Azophenyl Polyether/SnO₂ Nanocomposites for Information Encryption by Organic–Inorganic Interaction Control

Azobenzene-based polymers have been prominent photochromic materials (PCMs) for decades but still suffer from low efficiency and instability in photallochromy due to hindered isomerization in the solid state. Here, a controlled charge interaction between additive SnO₂ nanoparticles and azophenyl polyether was designed and established using density functional theory (DFT) prediction and experimental verification, aiming to disrupt <i>π</i>-<i>π</i> stacking among azobenzene moieties. Theoretical calculations, time-resolved fluorescence spectra, and zeta potential tests have proven that negative charges generated on the surface of SnO₂ nanoparticles under UV-A (330-370 nm) irradiation transfer to positively charged carboxyl groups of azobenzene moieties, accelerating the isomerization speed (response time ≤ 10 s) and stabilizing the <i>cis</i> conformation of azobenzene. Compared to the pristine azophenyl polyether films, the azophenyl polyether/SnO₂ composite film exhibits a more rapid and pronounced color-change behavior under both 450 nm blue light and 365 nm UV irradiation, enabling a stable and durable pattern writing/erasing functionality triggered by 450/365 nm light. Interestingly, owing to a 13.53% difference in reflectance at 410 nm between <i>cis</i> and <i>trans</i> isomers, the imprinted patterns on the composite films are nearly invisible under ambient light yet show a high contrast ratio (CR) of up to 2.4 under 405 nm violet light, demonstrating promising potential applications in anticounterfeiting and information encryption.