Photo-Responsive Azobenzene-Containing Inverse Opal Films for Information Security

Stimuli-responsive photonic crystals (PCs) have attracted increasing attentions owing to the unique optical feature in regulating the propagation of light and tunable structural colors in response to external stimuli, emerging application potential on diverse fields. However, the development of stimuli-responsive PCs with wide visible light range, broad shift of bandgaps, and adjustable responsive rates for counterfeiting remains challenging. Herein, a simple strategy for the preparation of photo-responsive azobenzene-containing inverse opal (AzoIO) films is reported. First, azobenzene-containing composites are generated by filling functional monomers into voids of silica colloids crystals. Followed by the thermal polymerization and subsequent etching, a series of AzoIO films are successfully fabricated with adjustable structural colors in wide visible wavelength. Upon irradiation with linearly polarized visible light (LPVL), a slowly broad blueshift of bandgaps (approximate to 138 nm, 3200 s) is observed due to the anisotropic shrinkage of the periodic PC structures. However, UV light irradiation contributed to a fast broad blueshift of bandgaps (approximate to 131 nm, 10 s), owing to the photoisomerization merit of azobenzene moiety. The proof-of-concept study on the applications in light-modulated multicolored writable paper, encryption films, and fast writing/erasing demonstrated the potential for information security. This work paves an avenue for developing promising optical anti-counterfeiting materials.