Cyanide and fluoride colorimetric sensing by novel imidazo-anthraquinones functionalised with indole and carbazole

Abstract

Novel imidazo-anthraquinones functionalised with indole and carbazole have been synthesised and characterised and their evaluation as colorimetric chemosensors was carried out in acetonitrile as well as in acetonitrile/H₂O (97:3) in the presence of several anions such as F⁻ , Cl⁻ , Br⁻ , I⁻ , CN⁻ , , , AcO⁻ , BzO⁻ , , , and . In addition, their behaviour in the presence of H⁺ and OH⁻  was also studied. Upon addition of CN⁻  and F⁻  to acetonitrile solutions of compounds 1–3, a marked colour change from yellow to orange was observed and the fluorescence emission of 1 and 2 was switched ‘on’. The recognition in organic aqueous solution leads to the selective and sensitive naked-eye detection (mM) of CN⁻  for all receptors, with an easily detectable colour change from yellow to orange. The binding stoichiometry between the receptors and the anions was found to be 2:1. The binding process was also followed by ¹H NMR titrations showing that two different binding modes occurred in the presence of fluoride or cyanide anions, which is in agreement with the spectrophotometric titrations.

Keywords::

• imidazole
• anthraquinone
• fluoride
• cyanide
• aqueous media
• naked-eye detection

Acknowledgements

Thanks are due to the Foundation for the Science and Technology (FCT, Portugal) for financial support to the NMR Portuguese network (PTNMR, Bruker Avance III 400-Univ. Minho), FCT and FEDER (European Fund for Regional Development)-COMPETE-QREN-EU for financial support to the Research Centre, CQ/UM [PEst-C/QUI/UI0686/2011 (FCOMP-01-0124-FEDER-022716)] and the post-doctoral grants to R.M.F. Batista (SFRH/BPD/79333/2011) and E. Oliveira (SFRH/BPD/72557/2010).