Theoretical study on a chemosensor for fluoride anion-based on a urea derivative



The sensing mechanism of the N-Phenyl-N′-(3-quinolinyl)urea (PQU) chemosensor for fluoride anion has been investigated by density functional theory/time-dependent density function theory. The double intermolecular hydrogen bonds are formed between the three anions (X[DOUBLE BOND]F, AcO, Cl) and the urea fragment of PQU. In the S0 states, the Hb[BOND]X hydrogen bonds are slightly stronger than the Ha[BOND]X hydrogen bonds and the fluoride-induced deprotonation occurs at the N[BOND]Hb position rather than at the N[BOND]Ha position. Consequently, the absorption peaks, including an intramolecular charge transfer transition and a ππ* transition, are significantly red-shifted. Thermodynamic calculations confirm that the deprotonation in the ground state is favorable in energy only when excess fluoride anion exists. Along with the S0 → S1 transition, the Ha[BOND]X hydrogen bonds strengthen and the Hb[BOND]X hydrogen bonds weaken. However, the emission spectra of [PQU-Hb], instead of [PQU-Ha], are observed upon addition of fluoride anion. © 2013 Wiley Periodicals, Inc.