Rhodamine-based derivatives for Cu2+ sensing: Spectroscopic studies, structure-recognition relationships and its test strips

A rhodamine spirolactam/2-hydrazinopyridine derivative was synthesized and characterized, which exhibited high selectivity to Cu2+ over other metal cations. The Cu2+ recognition of this rhodamine derivative could be detected by fluorescence spectra, absorption spectra and an obvious color change which was observed easily by naked-eyes. The binding of this rhodamine derivative to Cu2+ is instantaneous and sensitive. Moreover, a linear relationship was found between the fluorescence intensity at 575 nm from 0.5 × 10−6 M to 3.0 × 10−6 M of Cu2+ concentration, and the limit of detection (LOD) was at low concentration of 2.11 × 10−8 M, this would benefit for the establishment of standard working curves in practical Cu2+detection. Additionally, we synthesized rhodamine spirolactam/2-aminomethylpyridine derivative and rhodamine spirolactam/phenylhydrazine derivative as analogs for elucidate the structure-recognition relationships. Finally, we prepared the test strips of rhodamine spirolactam/2-hydrazinopyridine derivative for practical chromogenic the Cu2+ detection.

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► We designed and synthesized a rhodamine-based Cu2+ chemosensor of rhodamine spirolactam/2-hydrazinopyridine 1.
► It exhibited high selectivity to Cu2+ over other metal cations, and high sensitivity that could detect micromolar level of Cu2+ in aqueous solution. 1 could instantaneously and reversibly bind Cu2+ in 1:1 stoichiometry.
► Two analog compounds of rhodamine spirolactam/2-aminomethyl-pyridine 2 and rhodamine spirolactam/phenylhydrazine 3 were synthesized for the study of the structure-recognition activity relationship.
► Additionally, we also prepared the test strips of 1 for the practical Cu2+detection application.