A highly sensitive and selective colorimetric “Off-On” chemosensor for Cu²⁺ in aqueous media based on a rhodamine derivative bearing thiophene group

A new colorimetric “off-on” chemosensor based on rhodamine derivative bearing thiophene group has been synthesized. The chemosensor shows an excellent sensitivity and selectivity for Cu²⁺ over competing metal ions (Pb²⁺, Hg²⁺, Fe³⁺, Fe²⁺, Zn²⁺ Cd²⁺, Mn²⁺, Ba²⁺, Ag⁺ and Cr³⁺) in H₂O-EtOH solution (1/4, v/v). A distinctive peak at 561 nm appears in the UV–vis absorption upon the addition of Cu²⁺ in the rhodamine derivative solution and an obvious color change to be pink from colorless. The interaction of Cu²⁺ and the chemosensor are proven to adopt a 1:1 binding stoichiometry, and the recognition process is expected to be completed within 1 min. With a detection limit of 1.7 × 10⁻⁷ mol/L, the chemosensor shows great potential to monitor Cu²⁺ in environmental analysis systems.