| Summary: | The Lewis acidic redox-active and photoactive ruthenium(II) bipyridyl moiety in combination with amide (CO-NH) groups has been incorporated into acyclic, macrocyclic, and lower rim calix[4]arene structural frameworks to produce a new class of anion receptor with the dual capability of sensing anionic guest species via electrochemical and optical methodologies. Single-crystal X-ray structures of (1)Cl and (11)H2PO4 reveal the importance of hydrogen bonding to the overall anion complexation process. In the former complex, six hydrogen bonds (two amide and four C-H groups) stabilize the Cl- anion and three hydrogen bonds (two amide and one calix[4]arene hydroxyl) effect H2PO4 - complexation with 11. Proton NMR titration investigations in deuterated DMSO solutions reveal these receptors form strong and, in the case of the macrocyclic 5 and calix[4]arene-containing receptor 11, highly selective complexes with H2PO4 -. Cyclic and square-wave voltammetric studies have demonstrated these receptors to electrochemically recognize Cl-, Br-, H2PO4 -, and HSO4 - anions. The calix[4]arene anion receptor 11 selectively electrochemically senses H2PO4 - in the presence of 10-fold excess amounts of HSO4 - and Cl-. Fluorescence emission spectral recognition of H2PO4 - in DMSO solutions is displayed by 3, 5, and 11.
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