A Cu²⁺-selective naphthalimide–rhodamine based FRET fluorescent probe was synthesized and characterized.

In this work, a new rhodamine chemosensor (P) with excellent photochromic properties upon vis irradiation was designed and synthesized. The fabricated chemosensor P could detect Al³⁺ via the opening of the spirolactam ring of the rhodamine unit with high selectivity and sensitivity. The spirolactam ring opening was confirmed by NMR and infrared spectroscopy. Upon binding with Al³⁺, the generated 1 : 1 P-Al³⁺ complex, confirmed by Job's plot titrations and mass spectrometry analysis, could exhibit a remarkable fluorescence enhancement with a limit of detection (LOD) of 0.16 μM. Furthermore, the sensing of P to Al³⁺ in vivo was also studied quantitatively and qualitatively in detail, and the results showed that the coordination between P with Al³⁺ was reversible in living cells.

A new naphthalimide-based derivative L bearing an S-benzyldithiocarbazate moiety was synthesized as an “off–on” probe for Ag⁺. The new probe has high binding selectivity for Ag⁺ in water media with a detection limit of Ag⁺ down to 270 nM. Based on the Ag⁺-induced inhibition of a PET process and restriction of CN rotation, the coordination mode of 1 : 1 between L and Ag⁺ was proposed.

A small organic molecule P was synthesized and characterized as a fluorometric and colorimetric dual-modal probe for Hg²⁺. The sensing characteristics of the proposed probe for Hg²⁺ were studied in detail. A fluorescent enhancing property at 583 nm (>30 fold) accompanied with a visible colorimetric change, from colorless to pink, was observed with the addition of Hg²⁺ to P in an ethanol-water solution (8:2, v/v, 20 mM HEPES, pH 7.0), which would be helpful to fabricate Hg²⁺-selective probes with “naked-eye” and fluorescent detection. Meanwhile, cellular experimental results demonstrated its low cytotoxicity and good biocompatibility, and the application of P for imaging of Hg²⁺ in living cells was satisfactory.

A new Mg²⁺-selective fluorescent probe P was synthesized and characterized. With optimal conditions, the proposed probe P showed good selectivity to Mg²⁺ compared to other common metal ions, and worked in a wide linear range of 5.0 × 10⁻⁷–6.0 × 10⁻⁶ M with a detection limit of 1.7 × 10⁻⁷ M Mg²⁺ in ethanol-water solution (9:1, v/v, 20 mM HEPES, pH = 10.0).

A new fluorescent probe P based on rhodamine for Cu²⁺ was synthesized and characterized. The new probe P showed high selectivity to Cu²⁺ over other tested metal ions. With optimal conditions, the proposed probe P worked in a wide linear range of 1.0 × 10⁻⁶–1.0 × 10⁻⁵ M with a detection limit of 3.3 × 10⁻⁷ M Cu²⁺ in ethanol-water solution (9:1, v:v, 20 mM HEPES, pH 7.0). Furthermore, it has been used for imaging of Cu²⁺ in living cells with satisfying results.