393809-88-6Relevant articles and documents
Derivatization of 4-(dimethylamino)benzamide to dual fluorescent ionophores: Divergent spectroscopic effects dependent on N or O amide chelation
Malval, Jean-Pierre,Lapouyade, Rene
, p. 2439 - 2451 (2001)
Starting from the pentafluorophenyl ester of 4-(dimethylamino)benzoic acid, two dual fluorescent amide ligands with aza-15-crown-5 and 2-(aminomethyl)pyridine were obtained for sensing, respectively, alkali (alkaline-earth) and transition (heavy) metal cations. The crystal structure of the copper(II) complex is reported. The Cu2+ is coordinated through the pyridine N- and amide O-atoms of two symmetry-related ligands. The azacrown-directed Ca-chelation to the N-atom of the amide leads to a slight quenching of the two fluorescence bands. In contrast, the pyridine directed Cu11-chelation to the O-atom of the amide enhances the short-wavelength emission 17-fold over the locally excited state (LE), quenching the twisted intramolecular charge-transfer (TICT) emission, and, as a result, the intensity ratio I(LE)/I(TICT) provides an accurate and sensitive measurement of the Cu11 concentration. These different cation effects are dependent on which atom (N vs. O) of the amide function participates in cation coordination: while the Ca2+ interaction with the N-atom electron pair leads to the deconjugation of the amide N-atom from the fluorophore, Cu2+ interaction with the lone pair of the O-atom of the carbonyl group increases the energy of the n-π* but also of the 1La transition and therefore close the channel to the TICT state.
