Head-to-tail intermolecular hydrogen bonding of OH and NH groups with fluoride.
To explore the anion-recognition ability of the phenolic hydroxyl group and the amino hydrogen, we 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 (1)H NMR spectral studies revealed that receptor 1, having only a phenolic OH group, shows selective deprotonation of the hydroxyl proton towards F(-), which results in an "ON-OFF"-type signal in the fluorescence spectral studies. Receptor 2, which only has an amino hydrogen, also shows deprotonation of the amino hydrogen with F(-), whereas receptor 3 (having both OH and NH groups) shows head-to-tail intermolecular hydrogen bonding of OH and NH groups with F(-) prior to deprotonation. The observation of hydrogen bonding of the OH and NH groups in a combined solution of 1 and 2 with F(-) in a head-to-tail hetero-intermolecular 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 formation of an intermolecular hydrogen-bonding complex with F(-) prior to deprotonation. The presence of this hydrogen-bonding complex was confirmed by absorption spectroscopy, 3D emission contour studies, and (1)H NMR titration.
National Centre for Ultrafast Processes, University of Madras, Taramani Campus, Chennai-600 113, India.
Pichandi
P
Ashokkumar
Vayalakkavoor T
VT
Ramakrishnan
Perumal
P
Ramamurthy
D000641:Ammonia / Q000737:chemistry*; D000838:Anions; D005459:Fluorides / Q000737:chemistry*; D006860:Hydrogen Bonding; D017665:Hydroxyl Radical / Q000737:chemistry*
D000838:Anions; D017665:Hydroxyl Radical; D000641:Ammonia; D005459:Fluorides