A Colorimetric Mercury Ion Sensor

Significance

Colorimetric mercury ion (Hg²⁺) sensor 1 incorporates a dithia-dioxa-monoaza crown ether moiety that allows excellent selective binding of Hg²⁺ over other metal cations. A tricarbocyanine dye with benzyl groups on the nitrogen atoms of 3H-indo rings was chosen as the chromophore moiety for its relative photostability and near-infrared absorption. The absorption maximum of uncomplexed 1 is 695 nm (e = 86,000 M^-1 cm^-1) in methanol; titration with Hg²⁺ produces a large red shift in the absorption maximum to 817 nm (e = 190,000 M^-1 cm^-1). Consequently, the color of the solution changes from blue to nearly colorless upon addition of Hg²⁺. The association constant of 1 with Hg²⁺ in methanol was determined to be 4.335 × 10⁴ M^-1.