Multisite-complexation-regulating solvent-dependent monomolecular chemosensor for the quantification of Fe3+/ClO− and rapid detection of Al3+/Cr3+/Cu2+†

A versatile dihydroxylsalicylaldazine-containing fluorene (DHSF) compound was easily prepared through a one-step reaction. DHSF simultaneously exhibited solvent-regulating fluorescent OFF–ON behavior toward Al³⁺/Cr³⁺ and a dynamic OFF–ON–OFF fluorescent response toward Fe³⁺ in different aqueous DMF solutions with multiple absorption–ratiometric signals. These could be mainly attributed to the different binding modes between enol–keto isomers and Fe³⁺/Al³⁺/Cr³⁺, as proved by DFT calculation and IR spectroscopy results. Furthermore, DHSF displayed fluorescent OFF–ON–OFF and absorption–ratiometric dual responses to increasing ClO⁻ amounts. These results, together with the fluorescent ON–OFF changes from the metal displacement of the DHSF–Al³⁺/Fe³⁺ system by Cu²⁺, show that monomolecular DHSF is a versatile chemosensor for sensitively detecting Al³⁺/Cr³⁺/Cu²⁺ and quantitatively analysing Fe³⁺/ClO⁻ with practical application potential.