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'-(d imethylamino)-3,6-(tetraethylene glycol)flavone] and flavone lariat-crown e ther, were synthesized and characterized. The photophysical changes upon co mplexation with alkali and alkaline earth metal cations are explained in te rms of the enhancement of a cation-induced intramolecular charge transfer p rocess, 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 qu asi-cryptand and the charge density of the bound cation control the magnitu de of the photophysical changes. Based on the determination of stability co nstants between different cations and the macrocyclic ligand, our results i ndicate that the selectivity of flavone quasi-crown ether and flavone laria t-crown ether is better for the Ca2+ cation.