A rhodamine 6G derivative for turn-on detection of Fe³⁺ and Cr³⁺: Cell imaging studies

Fluorescent chemosensors that were reported for the recognition of metal cations like Cr³⁺ and Fe³⁺ usually resulted in the fluorescence quenching on interaction with the cations. Herein we report a rhodamine based compound (L-Bz) that produces pink coloration and strong fluorescence increment in the occurrence of Cr³⁺ and Fe³⁺ in acetonitrile/water (HEPES buffer, pH 7.4, 99.5:0.5, v/v). It was synthesized by a reaction between N-(rhodamine-6G)lactam-ethylenediamine (L1) and 4-benzyloxy 2-hydroxybenzaldehyde (L2) in ethanol. Its absorption intensity enhanced at 530 nm significantly and fluorescence intensity was amplified at 550 nm by 281- and 130-fold in the presence of Cr³⁺ and Fe³⁺, respectively. In the occurrence of these metal ions, spirolactam ring on L-Bz opens up to result the spectral changes. LOD values for Cr³⁺ and Fe³⁺ were determined in nM unit. Quantum yield and lifetime of L-Bz augmented in the presence of the cations. The rhodamine dye was utilized to sense the cations in HeLa cells.