Inkjet-Printable Hydrochromic Paper for Encrypting Information and Anticounterfeiting

Developing rewritable papers has gathered immense interest in recent times in view of developing sustainability in print media without exhausting environmental resources. We herein present a rapid and facile procedure for the fabrication of a communication medium by treating the surface of a paper with synthetic organic molecules, after which plain water could be used as an ink to print and reprint numerous times on the treated paper before disposal. Interestingly, as the paper comes in contact with water, the molecules are driven to reorganize in a slip-stacked arrangement. This alters their ground and excited state properties by hydrogen-bond-assisted nonradiative decay, in which the associated changes are visible to the naked eye. The changes evolved are sensitive to the solubility parameter of the solvent and thermally reversible, thus linking the hydrochromic property to the paper. Against a background of concerns over a rise in counterfeiting and leaks of confidential information, prospects for encrypted communications and anticounterfeiting is herein demonstrated.