Synthesis of Azulene Derivatives That Have an Azathiacrown Ether Moiety and Their Selective Color Reaction Towards Silver Ions

Abstract

Abstract Azulene derivatives that have an azathiacrown ether moiety were synthesized by using a modification of the method described by Vögtle and co‐workers. These compounds are highly selective for detecting Ag + ions, which is demonstrated visually by a color change from orange to violet. Structural studies of the Ag + ‐induced colored product by NMR spectroscopy and ESI‐MS identified a 1:1 (Ag + :ligand) complex formed by the coordination of Ag + ion with the azathiacrown ether moiety. Competition experiments in the presence of other metal ions, ESI MS/MS experiments on the Ag + and Hg 2+ complexes, and DFT calculations on the Ag + complex suggest that the high selectivity and color change for Ag + ion is due to the relatively strong binding of the azathiacrown ether moiety to Ag + ion, and not to π–cation interactions. Azulene derivatives that are highly selective toward a particular heavy metal ion and undergo a distinct color change have not been reported before.