Absorption- and fluorescence-spectral sensing of alkali metal ions in anionic micelle solutions containing crowned spirobenzopyrans

Spirobenzopyran derivatives bearing a monoazacrown ether moiety (monoaza‐12‐crown‐4, ‐15‐crown‐5, and ‐18‐crown‐6) and an octadecyl group as a lipophilic moiety, called crowned spirobenzopyrans were synthesized, which can be dissolved in anionic micelle solutions. We examined absorption‐and fluorescence‐spectral changes of micelle solutions containing a crowned spirobenzopyran on addition of alkali metal ions. The crowned spirobenzopyrans are in their merocyanine form in an anionic micelle solution even under dark conditions, showing a significant absorption in the visible region which is attributable to the merocyanine moiety. Crowned spirobenzopyran bearing a monoaza‐12‐crown‐4 moiety exhibited a drastic hypsochromic shift in the absorption and also an enhanced fluorescence on addition of Li+ to the micelle solutions under alkaline conditions. These spectral changes can be attributed to a strong interaction between Li+ bound by the crown ether moiety and a phenolate ion of the merocyanine moiety. Similar absorption and fluorescence‐spectral changes were induced in the anionic micelle solutions containing the other crowned spirobenzopyrans on addition of alkali metal ions. The intensity of the absorption‐spectral changes in the systems of the three crowned spirobenzopyrans, however, differed from each other, depending on the strength of interaction between a metal ion bound to the crown ether moiety and the phenolate ion of the merocyanine moiety. On the other hand, the extent of enhanced relative fluorescence intensity is dependent on the strength of interaction between metal ion and a nitrogen atom of azacrown ether moiety, because the fluorescence spectrum is quenched by photoinduced electron transfer (PET) from the nitrogen atom to the merocyanine moiety. Copyright © 2007 John Wiley & Sons, Ltd. Absorption‐ and fluorescence‐spectral changes of the anionic micelle solutions containing a crowned spirobenzopyran, which is spirobenzopyran derivatives bearing a monoaza‐12‐crown‐4, ‐15‐crown‐5 or ‐18‐crown‐6 moiety and an octadecyl group, were examined addition of alkali metal ions.