On the origin of chloride-induced emission enhancement in ortho substituted squaramides

Switching-On Fluorescence by Copper (II) and Basic Anions: A Case Study with a Pyrene-Functionalized Squaramide

“…Starting with the dye-displacement-based sensors, such as those reported by Costa [15], in recent years, a number of different approaches to fluorometric output has been reported. Starting with the dye-displacement-based sensors, such as those reported by Costa [15], in recent years, a number of different approaches to the design of molecular sensors have been developed [16,17]. The lack of related literature examples that act as efficient molecular sensors highlights the challenge in their design.…”

Squaramide-based receptors in anion supramolecular chemistry: insights into anion binding, sensing, transport and extraction

“…In the presence of polar solvents or anions, the intramolecular interaction was weakened or disrupted, suppressing the ESIPT and producing a variation of the fluorescence emission. In a more recent article, Muthyala et al 89 investigated in more detail the emission enhancement promoted by Cl − binding of ortho -substituted squaramides, investigating the three receptors 101 and 103–105 experimentally and computationally. The results suggest that this behaviour could ascribed to two degenerate excited states, resulting from two distinct competing charge transfer pathways.…”

Squaramides for colorimetric and fluorescent anion sensing

“…Similar design principles to those used in earlier work on thioureas have been used for the development of fluorescent squaramides for anion sensing, with reported examples of both receptor-spacerfluorophore squaramide based receptors, 18,37,38 and squaramides directly conjugated to the fluorophores. 11,39 The most effective fluorescent probes are those which give a ratiometric response to the analyte of interest. 40 Previously reported squaramide-based (and simple urea and thioureabased receptors) receptors have been demonstrated to give a fluorescent response to anions, however most simply reply upon a simple turn-on or turn-off change in fluorescence intensity.…”

“…Similar design principles to those used in earlier work on thioureas have been used for the development of fluorescent squaramides for anion sensing, with reported examples of both receptor – spacer – fluorophore squaramide based receptors, 18,37,38 and squaramides directly conjugated to the fluorophores. 11,39…”