A fluorescent chemosensor based on rhodamine for Cr3+ in red spectral region in aqueous solutions and living cells

A new rhodamine-based derivative (1) is designed as a colorimetric and fluorescent “off–on” chemosensor for Cr3+ in aqueous solutions. Its sensing behaviors toward metal ions in neutral aqueous solutions were investigated by UV–vis absorption and fluorescence spectroscopies. Compound 1 is found to exhibit a significant increase in absorbance at 581 nm and an amplified fluorescence at 600 nm toward Cr3+ in a preferential, sensitive and rapid manner. Upon addition of Cr3+, the spirolactam ring (colorless and nonfluorescent) of 1 was opened to form a ring-opened amide (purple red color and fluorescent) and a 1:1 stoichiometry for the 1-Cr3+ complex was formed with an association constant of 5.75×104 M−1. The quantification of Cr3+ by 1 using a fluorescence spectroscopy method was satisfactory in the linear working range below 4 μM, with a detection limit of 3.75×10–9 M for Cr3+ and good tolerance of other metal ions. The chemosensor has been used for imaging of Cr3+ in living Hela cells with satisfying results.