A dibenzo-16-crown-5 fluoroionophore for selective emission ratio sensing of Na+ in basic aqueous dioxane solution

For alkali metal cation sensing in aqueous dioxane solution,a novel dibenzo -16-crown-5 (+)(+) (DB 16C5) fluoroionophore 1, N-(pyren-1-yl)-sym-(propyl) dibenzo-16-crown-5-oxyacetamide, has been synthesized. Examination of fluor escent behavior for 1 in 4: 1 1,4-dioxane-water (v/v) containing tetramethy lammonium hydroxide (TMAOH) reveals that proton dissociation of the carboxa mido moiety is promoted by Na+ binding, which results in an emission ratio response due to internal charge transfer (ICT) from the donor carboxamido a nion to the pyrene acceptor. The emission intensity ratio (I-459/I-387) inc reases with enhancement of the Na+ concentration. No fluorescent response i s induced by the presence of Li+, K+, or Cs+. This high Na+ selectivity is attributed to a preorganized structure of DB16C5 lariat ether binding site in which Na+. binds tightly to the carbonyl oxygen of the side arm to induc e selective proton dissociation. Thus a ratiometric emission response with high Na+ selectivity has been obtained for 1 in 4: 1 1,4-dioxane-water (v/v ) containing TMAOH.