Fluorescent receptors are particularly useful for anion detection because they provide an easy indication of anion binding via emission spectra. A common challenge in the development of these sensors is controlling the direction of emission response, i.e. OFF-ON or ON-OFF. Our group has previously synthesized a 2,6-bis(2-anilinoethynyl)pyridine bis(amide) fluorescent receptor. Previous examples of this class of receptor with sulfonamides produced persistent dimers with inorganic acids and water. The amide receptor, however, is monomeric in solution and binds anions upon protonation of the pyridine. Here, the acid producing the lowest fluorescent emission response in the free receptor was determined. The fluorescence response increases with decreasing lypophilicity of the conjugate base, according to the Hoffmeister series. Anion competition studies are performed by adding anions to the protonated receptor and recording the emission spectrum. Hydrochloric acid produces the lowest emission intensity upon receptor protonation. The hydrochloric acid protonated receptor shows a strong increase in emission intensity when binding tetrafluoroborate. Further work may be done to tune the anion selectivity of pyridine bis(amide) receptors by altering the electron withdrawing and electron donating substituents on the receptor.

Counter-ions tune the fluorescent properties of a 2,6-bis(2-anilinoethynyl)pyridine bis(amide) anion receptor

251st National Meeting (2016)

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