Interaction of Ions in Organic and Aqueous Media with an Ion-Pair Sensor Equipped with a BODIPY Reporter: An ON1-OFF-ON2-ON3 Fluorescent Assay

Here, we present a ditopic ion-pair sensor, B1, containing the BODIPY reporter unit in its structure, which is shown to be able—thanks to the presence of two heterogeneous binding domains—to interact with anions in an enhanced manner in the presence of cations. This enables it to interact with salts even in 99% aqueous solutions, making B1 a good candidate in terms of visual salt detection in the aquatic environment. Receptor B1’s ability to extract and release salt was applied in the transport of potassium chloride through a bulk liquid membrane. Working with a concentration of B1 in the organic phase and with the presence of a specific salt in an aqueous solution, an inverted transport experiment was also demonstrated. By varying the type and the amount of the anions added to B1, we were able to develop diverse optical responses, including a unique four-step ON1-OFF-ON2-ON3 output.