Crystallization-Induced Emissive Invisible Ink

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.