Crystallization‐Induced Emissive Invisible Ink

Abstract Crystallization‐induced emission (CIE) has been reported for a handful of polyaromatic molecules, and this phenomenon has been generally ascribed to blocking of nonradiative energy dissipation pathways through crystalline organizations. Herein, the first use of a single‐ring CIE‐based “invisible” ink is reported, which can be applied on varied surfaces. The ink comprises (3E)‐4‐[4‐(methylsulfanyl)phenyl]‐3‐buten‐2‐one (MSPB), exhibiting remarkable spontaneous water and interface‐induced CIE. The molecule, which is synthesized through a facile one‐step process, is nonfluorescent when dissolved in polar organic solvents but forms fluorescent crystalline assemblies upon addition of water or upon drying on solid substrates. X‐ray diffraction analysis reveals that the fluorescent crystalline structure of MSPB is stabilized both by intermolecular C⋅⋅⋅HO and C⋅⋅⋅Hπ interactions among adjacent molecules. The readily adopted crystalline organization of MSPB facilitates its use as a fluorescent ink on diverse substrates, including paper, metals, polymers, and ceramic surfaces.