METAL ION AND ANION BINDING STUDIES OF NEWLY DESIGNED ACRIDINEDIONE BASED FLUORESCENT CHEMOSENSORS

  • Posted by Ashokkumar
  • January 28, 2011 8:34 PM PST
  • 0 comments
  • 2,956 views

Understanding the host-guest interaction is a main key in the design of selective and sensitive chemosensors. In the present thesis, detailed steady state, time-resolved fluorescence and 1H NMR spectroscopic studies have been carried out to elucidate the metal ion and anion interaction with various receptors linked acridinedione (ADD) fluorophore. In the first part, a series of ADD based bichromophoric podand systems with varying chain length of oxyethylene receptor and electron donating –OCH3 group were synthesized as a metal ion sensor.1 Addition of Ca2+ leads to the folding of the bichromophore and results in the fluorescence enhancement due to the suppression of PET process. This is the first report based on the PET signaling mechanism in acyclic polyether based sensors. In the second part, effect of solvent on metal ion and anion recognition ability of ADD based heteroditopic host has been described.2 Depending on the solvent polarity selectivity of the metal ion binding and the nature of the anion interaction, namely H-bonding and deprotonation is varied. Simultaneous binding studies of metal ion and anion shows the sequestering of ions due to the absence of cooperative binding between the two kinds of ions.3 The present study clearly signifies the role of solvent in metal ion selectivity, which is often unnoticed parameter in metal ion sensors. In the third part, the H-bonding and deprotonation equilibrium between anions and thiourea have been investigated.4 Addition of AcO- and H2PO4- results in the genuine hydrogen bond complexation as proved from 1H NMR and optical spectral studies. Whereas, the addition of F- results in the two stepwise changes in both absorption and emission spectra. Interestingly, two new emission maxima are observed depending on the concentration of F-. Excitation, 3D emission contour, time-resolved emission spectra (TRES), time-resolved area normalized emission spectra (TRANES) and 1H NMR titration spectra clearly indicating the presence of stepwise H-bonding and deprotonation equilibrium between F- and thiourea. This is the first fluorescence spectral evidence of anion-receptor H-bonding and deprotonation equilibrium. In the fourth part, anion recognition ability of phenolic hydroxyl group and amino hydrogen were assessed from three different ADD linked anion receptors having OH, NH and combination of OH and NH groups.5 Dyes having only phenolic OH group and only NH group are showing deprotonation selectively towards F-. Whereas, the receptor having both OH and NH groups show a novel head-to-tail intermolecular hydrogen bonding of OH and NH groups with F-, which was proved from excitation, 3D emission contour, 1H NMR titration and 1H-1H COSY spectra.

0 comments