Double layer 3D codes: fluorescent supramolecular polymeric gels allowing direct recognition of the chloride anion using a smart phone.

Reported here is a two-layer gel construct that permits the on-site detection of the chloride anion by means of a hand-held UV-vis lamp and a smart phone "app". To prepare this system, eight fluorescent polymeric gels G1-G8 were synthesized. Gels G1-G4 containing C4P/imidazolium-F anion recognition motifs were used to construct a fluorescent pattern (Code A) that may be read out by a smart phone as a 3D color code (Info A). Gels G5-G8, which are based on C4P/imidazolium-Br anion interactions, were used to construct an array (Code B) that may be read as Info B. Code B was then adhered to the surface of Code A to produce an adhered double layer code system stabilized by interfacial C4P/imidazolium-Br anion interactions. Readout of the top layer (Code B) could be achieved without interference from Code A. Treatment with a Cl anion source was found to delaminate the top layer and leave intact the more robust bottom layer, allowing the bottom layer (Code A) to be read out. The disparate information content associated with Codes A and B thus permits the on-site recognition of Cl. The present sensing strategy does not rely on elaborate instrumentation and could provide a new application for elaborated soft materials.