New fluorescent metal receptors based on 4,4′-carbonyl bis(carbamoylbenzoic) acid analogues with naphthalene fluorophore

Abstract

In this manuscript is described a research related with two ditopic receptors based on 4,4′-carbonyl bis(carbamoylbenzoic) acids bearing a naphthyl (2a) and naphthylmethyl fluorophores (2b), which interact with metal ions. The fluorescence properties of both receptors were influenced by the connectivity with the amide group. The non-spaced receptor 2a presents an electron delocalisation from the amide to the naphthyl group having a broad red-shifted emission band and high quantum yield. The spaced receptor 2b presented a photo-induced electron transfer (PET) process from the amide to the naphthyl group, and a structured emission band is present at the UV region with low quantum yield. The different chemical structure influenced the fluorescent response used to analyse the coordination with metallic ions. The 2a receptor has an ON–OFF response because of the inhibition of the ICT process. The 2b receptor shows an OFF–ON response because of the inhibition of the PET process. Additional analytical studies by 1H-NMR and FTIR demonstrated the strong interaction of the amide and carboxylic functional groups with the metallic ions. Competitive experiments with EDTA showed that a very stable complexes are obtained between metallic ions and the new receptors.