A naphthalimide–rhodamine ratiometric fluorescent probe for Hg2+ 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.

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► A fluorescent probe for Hg2+ based on Hg2+-promoted desulfurization reaction.
► Ratiometric fluorescent sensing for Hg2+ based on FRET.
► Excellent selectivity and high sensitivity toward detecting Hg2+.
► The large Stokes shift (185 nm) can be realized in this system.