| Abstract
| - Spirobenzopyrans bearing monoazathiacrown ethers and noncyclic analogues were synthesized,and their ion-responsive photochromism depending on the dual metal ion interaction with the crownether and the phenolate anion moieties was examined using alkali and alkaline-earth metal ions,Ag+, Tl+, Pb2+, Hg2+, and Zn2+. The prepared spirobenzopyrans showed a selective binding abilityto Mg2+ and Ag+ with negative and positive photochromism, respectively. Among the metal ions,only Ag+ facilitated photoisomerization to the corresponding merocyanine form. Depending on thering size of the monoazathiacrown ether moieties, soft metal ions such as Hg2+ and Ag+ showedsignificant shifts in the UV−vis absorption spectra, while hard metal ions such as Mg2+, Zn2+, andPb2+ did not afford any meaningful shift. This result reflects that the monoazathiacrown etherand phenolate anion moieties prefer soft and hard metal ions, respectively. Therefore, the Mg2+and Ag+ selectivities are mainly derived from the phenolate anion and monoazathiacrown ethermoieties, respectively. On the other hand, a spirobenzothiapyran bearing 3,9-dithia-6-monoazaundecane showed a remarkable selectivity to Ag+.
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