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 − F − , AcO − , Cl − ) and the urea fragment of PQU. In the S 0 states, the H b X − hydrogen bonds are slightly stronger than the H a X − hydrogen bonds and the fluoride‐induced deprotonation occurs at the NH b position rather than at the NH a 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 S 0 → S 1 transition, the H a X − hydrogen bonds strengthen and the H b X − hydrogen bonds weaken. However, the emission spectra of [PQU‐H b ] − , instead of [PQU‐H a ] − , are observed upon addition of fluoride anion. © 2013 Wiley Periodicals, Inc.