Spectroscopic Study of a Symmetrical Bis-crown Fluoroionophore of the Diphenylpentadienone Series

A new fluoroionophore bearing two crown ethers on the conjugated system, 1,5-bis[4N-(aza-15-crown-5)phenyl]-1,4-pentadien-3-one (II), was synthesized together with model compound I where the crown ethers are replaced by diethylamino groups. The behavior of molecules I and II in the presence of alkali and alkaline-earth perchlorates was investigated in acetonitrile solution by absorption and emission spectroscopy (including picosecond techniques), mass spectrometry, and NMR spectroscopy. Two types of interaction must be distinguished:  on the one hand, the expected complexation of the crown ether moieties, which generated strong spectroscopic effects with Na⁺, Li⁺, Ba²⁺, and Ca²⁺ ions, and on the other hand, an interaction between the unsaturated ligand core and the cation, particularly noticeable with magnesium. The absorption data were correctly fitted by taking into account three different stoichiometries and the corresponding association constants were calculated. The emissive properties of the species involved were discussed.