A colorimetric and ‘OFF–ON’ fluorometric chemosensor based on a rhodamine-pyrazole derivative for the detection of Al³⁺, Fe³⁺and Cr³⁺metal ions, and its intracellular application

Abstract

The colorimetric and fluorescence responses of a new rhodamine-functionalized probe (<i>E</i>)-2-(((5-chloro-3-methyl-1-phenyl-1<i>H</i>-pyrazol-4-yl)methylene)amino)-3',6'-bis(diethylamino)spiro[isoindoline-1,9'-xanthen]-3-one (RMP) are investigated. RMP has been thoroughly characterized using various spectroscopic tools and single crystal X-ray diffraction. Among different competing cations, it shows highly sensitive colorimetric and "OFF-ON" fluorescence responses towards Al³⁺, Fe³⁺and Cr³⁺metal ions. The spectral shifts are clearly noticeable in the visible region of the absorption spectrum and can be observed with the naked eye. Fluorescence quantum yield, stoichiometric ratio, binding constant and detection limit of RMP towards Al³⁺, Fe³⁺and Cr³⁺metal ions have been calculated. Furthermore, RMP-M³⁺ complexes are reversible and sensitive to EDTA, which effectively mimics a molecular logic gate. Al³⁺, Fe³⁺and Cr³⁺metal ions have been further applied in intracellular application in model human cells.