A naphthalimide-rhodamine ratiometric fluorescent probe for Hg based on fluorescence resonance energy transfer

On the basis of fluorescent resonance energy transfer from 1,8-naphthalimide to rhodamine B, a new fluorophore dyads (4) containing rhodamine B and a naphthalimide moiety was synthesized as a ratiometric fluorescent probe for detecting Hg²⁺ with a broad pH range 5.7-11.0. The selective fluorescence response of 4 to Hg²⁺ is due to the Hg²⁺-promoted desulfurization of the thiocarbonyl moiety, leading to the ring-opening of rhodamine B moiety of 4. When 4 was employed at 0.1 μM with the slit size being 20 nm/20 nm, a low level of Hg²⁺ (up to 3 × 10⁻⁸ M) can be detected using the system.