A hybrid hydrochromic molecular crystal applicable to invisible ink with high reversibility

Abstract

Invisible–visible printing with visibility controlled sensitively by hydrochromic materials is a perennially interesting scientific topic. A new hydrochromic invisible ink material, (C₈H₂₀N₂)[Mn(NCS)₄(H₂O)₂] (1), for rewritable or confidential printing is proposed and successfully demonstrated using water as the sole trigger to switch the hydrochromic dye on a solid medium. Additionally, it maintains reversible and sensitive reliability after continuous erasing and rewriting dozens of times without color fading.