Strapped calix[4]pyrroles bearing a 1,3-indanedione at a beta-pyrrolic position: chemodosimeters for the cyanide anion.

A strapped calix[4]pyrrole bearing a 1,3-indanedione group at a beta-pyrrolic position has been synthesized and studied as a ratiometric cyanide-selective chemosensor. A concentration-dependent bleaching of the initial yellow color was observed upon addition of the cyanide anion. The bleaching, which was observed exclusively with the cyanide anion, occurred even in the presence of other anions. Spectroscopic studies provide support for a mechanistic interpretation wherein the cyanide anion forms a complex with the receptor (K = 2.78 x 10(4) M(-1)) through a fast equilibrium, which is followed by slow nucleophilic addition to the beta-position of the 1,3-indanedione group. A minimum inhibitory effect from other anions was observed, a feature that could be beneficial in the selective sensing of the cyanide anion.