The complexation of flavone derivatives with alkali and alkaline earth metal cations studied by spectroscopic methods

A new kind of fluoroionophore, typified by flavone quasi-crown ether [4'-(dimethylamino)-3,6-(tetraethylene glycol)flavone] and flavone lariat-crown ether, were synthesized and characterized. The photophysical changes upon complexation with alkali and alkaline earth metal cations are explained in terms of the enhancement of a cation-induced intramolecular charge transfer process, which results from the interaction between the bound cation and the carbonyl group of the flavone. The size and shape of the quasi-crown or quasi-cryptand and the charge density of the bound cation control the magnitude of the photophysical changes. Based on the determination of stability constants between different cations and the macrocyclic ligand, our results indicate that the selectivity of flavone quasi-crown ether and flavone lariat-crown ether is better for the Ca2+ cation.