Alkali metal recognition induced isomerization of spiropyrans

We report herein the preliminary results obtained for spiropyrans 4 bearing a monoaza-crown ring (1) as a recognition site, of which isomerization to the colored merocyanines (2) is induced by recognition of alkali-metal cations. This new type of chromoionophore is conceptually different from the crown ether dyes so far synthesized, because in the latter cases, the absorption bands of chromophores are merely shifted by the complexation of cations