A Sensitive and Selective Mercury(II) Sensor Based on Amplified Fluorescence Quenching in a Conjugated Polyelectrolyte/Spiro‐Cyclic Rhodamine System

A novel fluorescence‐based sensor for mercury(II) ion is described consisting of a water‐soluble, anionic‐conjugated polyelectrolyte (CPE) and spiro‐cyclic rhodamine derivative ( 1 ). A solution containing the CPE (0.1 × 10 −6 M repeat unit concentration) and 1 (1 × 10 −6 M concentration) in aqueous solution exhibits a sensitive and selective turn‐off fluorescence response to Hg(II). The Stern–Volmer quenching constant for quenching of the fluorescence of the system by Hg(II) is ≈1.5 × 10 7 M −1 , and Hg(II) can be sensed with a detection limit <10 × 10 −9 M. A mechanism for the sensor response is proposed and it consists of efficient and selective complex formation between 1 and Hg(II), along with a very high association between the 1‐ Hg(II) complex and the anionic CPE.