A highly sensitive and selective ratiometric and colorimetric sensor for Hg²⁺ based on a rhodamine-nitrobenzoxadiazole conjugate

An effective Hg²⁺-specific probe (1) was designed and prepared based on a rhodamine-nitrobenzoxadiazole conjugate. The sensing behavior of this probe was studied by UV-visible and fluorescence spectroscopy. With Hg ²⁺, the probe displayed both colorimetric responses and ratiometric changes. The ratio of the absorption intensities at 525 and 460 nm for the two chromophores in the probe increased from 0.17 to 0.46. The probe exhibited excellent selectivity and sensitivity towards Hg²⁺ over other metal ions, which could be attributed to the Hg²⁺-triggered ring opening of the spirolactam of the rhodamine moiety and the formation of a 1:1 1-Hg ²⁺ complex.