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.
