Reversible fluorescent and colorimetric rhodamine based-chemosensor of Cu2+ contact ion-pairs using a ditopic receptors

•Reversible rhodamine-based sensors were designed and synthesized as ditopic receptors.•L1 and L2 were chemosensors selective for AcO−.•Cu2+ induced the Em-FRET on process.•Em-FRET off was done by adding AcO−.•The complexes with anions in the presence and absence of Cu2+ exhibited positive cooperativity.

Rhodamine chemosensors based on excimer-fluorescent resonance energy transfer (Em-FRET), combined with energy donor from excimer emission (naphthalene excimer) and energy acceptor from dye absorption (rhodamine dye) (L1) and fluorescent chemosensor (L2) were designed and synthesized. Complexation studies using UV–vis absorption and fluorescence spectroscopy showed that L1 and L2 were chemosensors selective for AcO−. Allowing the chemosensors L1 and L2 to complex with Cu2+ resulted in a hyperchromic shift of UV–vis absorption and a quenching of fluorescence in the presence of anions such as AcO−, F−, BzO− and H2PO4−. The incremental stability constants of anion complexation upon addition of Cu2+ were illustrated due to the allosteric effect and inductive effect from Cu2+ complexation. The adduct L1·Cu2+ could still be used to detect AcO−, whilst the adduct L2·Cu2+ turned out to bind BzO−.

Graphical abstractRhodamine chemosensors based on excimer-fluorescent resonance energy transfer (Em-FRET), combined with energy donor from excimer emission (naphthalene excimer) and energy acceptor from dye absorption (rhodamine dye) (L1) and fluorescent chemosensor (L2) were designed and synthesized. Complexation studies using UV–vis absorption and fluorescence spectroscopy showed that L1 and L2 were chemosensors selective for AcO−. Allowing the chemosensors L1 and L2 to complex with Cu2+resulted ina hyperchromic shift of UV–vis absorption and a quenching of fluorescence in the presence of anions such as AcO−, F−, BzO− and H2PO4−. The incremental stability constants of anion complexation upon addition of Cu2+ were illustrated due to the allosteric effect and inductive effect from Cu2+ complexation. The adduct L1•Cu2+ could still be used to detect AcO−, whilst the adduct L2·Cu2+ turned out to bind BzO−.Figure optionsDownload full-size imageDownload as PowerPoint slide