Abstract:The effects on the photophysical properties of three crown ethers (1 a ± c) containing the 1,8-dioxyxanthone residue caused by the complexation with Ba 2 , Sr 2 , and Ca 2 metal ions are reported. The strong enhancement of the fluorescence, the appearance of a long-lived delayed fluorescence, and a good selectivity towards Ba 2 ions prove that 1 c is an efficient fluorescent chemosensor for this ion. In addition, the range of selectivities shown by this family of crown ethers towards the alkaline earth metal ions together with their favorable photophysical properties, make them suitable for the construction of (multi)sensory devices. The differences in the photophysical properties between the uncomplexed and complexed crown ethers can be accounted for by the stabilization of a different ground state conformer of the dioxyxanthone moiety by the metal ion within the cavity of the crown ether.