Dual-responsive photonic multilayers in combination with a smartphone application as high-security anti-counterfeiting devices

Abstract

A new concept for dual-responsive one-dimensional (1D) photonic crystal (PC) multilayers is proposed herein. The novel PC-based systems rely on the humidity from the human breath and fluorescence triggered by Al3+ coordination to act as high-security anti-counterfeiting labels to be used in combination with a smartphone application. The dual-responsive patterned film is fabricated via the alternating deposition of photo-crosslinkable poly(2-vinylnaphthalene-co-benzophenone acrylate) and 51%-quaternized poly(4-vinylpyridine-co-benzophenone acrylate) onto a transparent polyethylene terephthalate substrate to obtain 1D PC multilayers, followed by the introduction of a poly([(2-hydroxybenzylidene)-4-vinylbenzohydrazide-co-benzophenonyl acrylate) top coating. The obtained system is then exposed to ultraviolet light irradiation through variously patterned masks. The patterned films exhibit vivid dual color transitions in high-humidity environments along with remarkable turn-on fluorescence, following the coordination of Al3+ ions upon spraying with a 1 wt% Al(NO3)3 solution. Notably, the efficacy of the combination between the two-step security function of the flexible patterned multilayer films and a smartphone app was also demonstrated. The first level of security involves the determination of the RGB color value before and after a color change triggered by blowing onto the film. The second level of security involves the revelation of hidden fluorescent shapes under ultraviolet light irradiation after Al(NO3)3 spraying.