Stepwise structural transformation in hybrid antimony chloride for time-resolved and multi-stage informational encryption and anti-counterfeiting†

The growing issue of counterfeiting has driven an increasing demand for advanced anti-counterfeiting technologies. Stepwise structural transformations among numerous compounds offer a promising approach to achieving high-level anti-counterfeiting methods, such as multi-step and time-resolved techniques. However, research in this area is still in its early stages. In this work, we report the first example of the stepwise structural transformation from ASbX₄ (A = cation, X = halide) to A₂SbX₅ and further to A₃SbX₆. The compounds are [Bzmim]₄[Sb₄Cl₁₆] (1, Bzmim = 1-benzyl-3-methylimidazolium), [Bzmim]₂SbCl₅ (2) and [Bzmim]₃SbCl₆ (3). 1, 2, and 3 exhibit distinct photoluminescent properties: non-emission, red emission peaking at 600 nm, and green emission peaking at 525 nm, respectively. Consequently, stepwise structural transformations enable stepwise luminescent switching from an “off” to multi-“on” states. Moreover, the switching mode can be adjusted from “off-on” to “off-on¹-on²” by simply changing the reactant ratio. Using SbCl₃ ethanol solutions as invisible ink, multi-step and time-resolved information encryption and anti-counterfeiting were demonstrated by combining [Bzmim]Cl solution, UV light, time, and temperature as developers. The tunable composition and photoluminescent response modes of these IOMHs position them as excellent candidates for high-level information encryption and anti-counterfeiting applications. This work sheds light on the potential for developing advanced informational encryption technologies.