Turn-on fluorogenic and chromogenic detection of Fe3+ and Cr3+ in a completely water medium with polyacrylamide covalently bonding to rhodamine B using diethylenetriamine as a linker

Abstract

A new monomeric fluorophore N-acryl-N′′-(rhodamine B-yl) diethylenetriamine (ARBD) was synthesized. Free radical precipitation copolymerization was carried out in order to prepare a water-soluble fluorescent copolymer (poly(AM–ARBD)), based on acrylamide. The chemical constitution of poly(AM–ARBD) was studied by FTIR and ¹H NMR spectroscopy. The fluorescent characteristic of the aqueous solutions of the copolymer was investigated both in varied pH and in the presence of metal cations. It was found that polymeric sensors exhibited high selectivity and sensitivity in colorimetric and fluorescence responses toward Fe³⁺ and Cr³⁺ over other metal ions. The polymeric sensors were non-fluorescent in the spirolactam form and could be selectively converted into the fluorescent ring-opened amide form in the presence of Fe³⁺ or Cr³⁺ ions that lead to fluorescence enhancements and colorimetric changes from colorless to red or pink, respectively. Fe³⁺ and Cr³⁺ can be sensed with a detection limit at 1.34 × 10⁻⁴ and 9.90 × 10⁻⁶ mol L⁻¹, respectively. The combination of water solubility and positive fluorescence response as well as color change is therefore particularly promising for the practical utility of this sensor.