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 π–π 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 cis 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 cis and trans 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.