The photophysics of some 3-hydroxyflavone derivatives in the presence of protons, alkali metal and alkaline earth cations

The absorption and fluorescence properties of three monoaza crown ether (either 15-crown-5 or 18-crown-6 substituted at the 4′-position) 3-hydroxy- and 3-methoxy-flavone compounds in the presence of protons, alkali metal and alkaline earth cations are reported. The corresponding 4′-dimethylamino-flavones were also studied for comparison. All the compounds protonate in moderate acid (tens of mM H+) with significant changes in emission only being observed for the 3-methoxy derivatives. The crown ether compounds bind the alkaline earths with binding constants of the order of 104 dm3 mol−1 and with two moles of metal ion being bound at high concentrations.