Structural and photochemical aspect of metal-ion-binding to a photochromic chromene annulated by crown-ether moiety

Complexation between a benzopyran entity annulated with a 15-crown-5 ether unit and three metal cations, Mg2+, Ba2+, and Pb2+ has been investigated by UV–vis and NMR spectroscopy. The complexes composition, the stability constants and the structural arrangements have been determined. The photochemical and thermal properties of the photochromic benzopyran derivative in absence and in the presence of metals have been studied. The metal-ion-binding ability of the fused macrocyclic entity drastically modifies photochromism by decreasing the thermal stability of photomerocyanines, whereas the metal cations are partially ejected from crown-ether cavity when benzopyran is in open configuration.