About the use of an amide group as a linker in fluoroionophores: competition between linker and ionophore acting as chelating groups

The photophysical and complexing properties of a series of aza-crown fluoroionophores based on coumarin 343 and on 3- and 6-methoxynaphthoic amides in acetonitrile are reported. The goal of the work was to probe the participation of the amide bridge linking the fluorophore and the ionophore in the metal chelation. The use of 3- and 6-methoxy substituents in the naphthoic amide fluorophores allowed us to maintain the charge transfer character of the system and to probe the participation of the methoxy group as ancillary ligand. The aza-crown unit is no longer complexing when the amide linker is included in a β-dicarbonyl sub-structure. The amide function itself is still able to form complexes, even if weaker, with the cations.