A dansyl–rhodamine chemosensor for Fe(III) based on off–on FRET

• The chemosensor was synthesized relatively in a simple way.
• The skeleton of the chemosensor is composed of a dansyl and rhodamine group.
• Off-on FRET was induced by Fe3+ binding to the chemosensor.
• The chemosensor showed high selectivity and sensitivity for Fe3+.

A novel fluorescent chemosensor bearing a rhodamine and a dansyl moiety was developed for highly selective detection of Fe3+ based on fluorescence resonance energy transfer (FRET) mechanism. Binding of Fe3+ to the chemosensor induced spirolactam ring opening in the rhodamine moiety and subsequent off–on FRET from the dansyl energy donor to the rhodamine energy acceptor due to the spectral overlap between the emission of the dansyl moiety and the absorption of the ring opened rhodamine moiety. Job’s plot analysis indicated a 1:1 binding stoichiometry between the chemosensor and Fe3+. The association constant was estimated to be 2.72 × 103 M−1 according to the Benesi–Hildebrand method. With the feature of easy synthesis, simple structural skeleton and excellent sensing ability, the newly synthesized chemosensor provided the potential for applying as a highly selective fluorescent probe in complex samples containing various competitive metal ions and developing other metal ion chemosensors to fulfill various needs of biological and environmental field.

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