To explore the anion recognition ability of phenolic hydroxyl group and amino hydrogen, we have synthesized three different acridinedione (ADD) based anion receptors 1, 2 and 3 having OH, NH and combination of OH and NH groups respectively. Absorption, emission and 1H NMR spectral studies revealed that the receptor 1 having only phenolic OH group shows deprotonation of the hydroxylic proton selectively towards F-, and results in the “ON-OFF” type signal in the fluorescence spectral studies. Receptor 2 having only amino hydrogen also shows deprotonation of amino hydrogen with F-; whereas, receptor 3 having both OH and NH groups show head-to-tail intermolecular hydrogen bonding of OH and NH groups with F- prior to deprotonation. Observation of hydrogen bonding of OH and NH groups in combined solution of 1 and 2 with F- in a head-to-tail heterointermolecular fashion and the absence of head-to-head and tail-to-tail intermolecular hydrogen bonding in 1 and 2 with F- prove that the difference in the acidity of the OH and NH protons leads to the intermolecular hydrogen bonding complex formation with F- prior to deprotonation. Presence of hydrogen bonding complex was confirmed by absorption, 3D emission contour and 1H NMR titration spectra.
ChemPhysChem 2011, 12, 389 – 396