Fluoride recognition by a chiral urea receptor linked to a phthalimide chromophore

Abstract

The anion chemosensor 1 based on a urea-activated phthalimide with a stereogenic centre was synthesized using an efficient procedure involving a Curtius rearrangement. Its photophysical properties were estimated in several solvents. Sensor 1 detected fluoride with absorption as well as fluorescence changes and was only observable for this case and not for other halides. The appearance of a new CT complex emission at a longer wavelength and no changes in the singlet lifetime of 1 in the presence of fluoride supported a fluorescence static quenching mechanism. 1H-NMR studies, together with theoretical calculations based on DFT methods at the B3lYP/6-31G* level of theory confirmed the formation of a [1-F]- complex through H-bonding interactions rather than receptor deprotonation in the recognition process. Reversibility of this process was observed upon addition of a protic solvent.

Anion binding with urea and thiourea derivatives

“…The dissociation process induced by the addition of AcO -could be further shifted toward deprotonation by elimination of the formed acetic acid, using the excess of anion which led to halides, selectivity for F -in CH 3 CN, but the deprotonation did not take place [24]. They also synthesized thiourea analogue of receptor 11 (Fig.…”

Fluorescent sensors for ions based on organic structures

“…6 A selective colour change from colourless to yellow with the appearance of a green fluorescence was exhibited by 8 in the presence of F À and such changes were attributed to an interaction between the indolic NH proton and F Griesbeck et al, achieved selective fluoride recognition, by using the chemosensor 9 which is based on a chiral urea-phthalimide conjugate. 7 Upon recognition of F À , the sensor 9 was reported to exhibit changes in both its absorption and fluorescence spectra when recorded in acetonitrile solution. Upon titration with F À , the absorption spectrum of 9 was red-shifted with the appearance of three isosbestic points at 258, 317 and 342 nm, respectively while its emission spectrum (l exc = 340 nm) exhibited a complete switching-off of emission intensity upon increasing concentration of F À .…”

Nuclear Magnetic Resonance Spectroscopy Investigations of Naphthalene-Based 1,2,3-Triazole Systems for Anion Sensing

“…A number of colorimetric and fluorometric sensors have been developed to detect anions through a Brønsted acid-base reaction and/or hydrogen bond formation at the N-H and O-H moieties [18]. For ion recognition, complicated molecules with multistep syntheses are used to create highly conjugated systems with common scaffolds such as ureas, amides, and/or phenolic groups [19,20]. Photoinduced electron transfer (PET) [21,22], metal-to-ligand charge transfer (MLCT) [22,23]; excimer/exciplex formation [23], intramolecular charge transfer (ICT) [24]; and excited state intra/intermolecular proton transfer (ESPT) [25,26] are some of the signaling mechanisms by which the anions are detected.…”