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A rhodamine-B based chemosensor with diphenylselenium, RhoSe, has been synthesized, and its detection behavior towards various metal ions is studied via UV/Vis and fluorescence spectroscopy. RhoSe shows a selective response to Hg2+ in CH3OH/H2O (v/v = 9 : 1) solutions over other metal ions. After addition of Hg2+, the solution of RhoSe displays an obvious color change from colorless to pink and a significant, 48-fold fluorescence enhancement. The color change and fluorescence enhancement are attributed to the ring-opening of the spirolactam in the rhodamine fluorophore, which is induced by Hg2+ binding. The binding ratio of RhoSe–Hg2+ was determined by a Job plot as a 1 : 1 ratio, and the effective pH range for Hg2+ detection was 4.0–10. Importantly, the reversibility of the RhoSe–Hg2+ complex was observed through the addition of Na2S. For practical applications, the strip method was utilized to detect Hg2+ in water/methanol solution. In addition, confocal fluorescence microscopy experiments demonstrated that RhoSe is an effective fluorescent probe for Hg2+ detection in vitro and in vivo.

Novel fluorogenic receptors S1–S4 (imidazo anthraquinone derivatives) were synthesized from o-substituted benzaldehyde and 1,2-diaminoanthraquinone and characterised with various spectroanalytical techniques. In the case of S1, the selectivity towards cyanide ions with turn-on fluorescence output among other anions, due to the inhibition of the twisted intramolecular charge transfer (TICT) mechanism. The effect of substitution was successfully compared with sensing studies of S2–S4. S1 showed a good binding constant with a 1 : 1 stoichiometric ratio and micromolar detection limit. The sensing behaviour was further supported by 1H NMR titration, TD-DFT calculations and lifetime measurement studies. S1 was applied for the bio-imaging of the cell line RAW264.7 and successfully sensed cyanide ions under physiological conditions.