Naphthyl-imidazo-anthraquinones as novel colorimetric and fluorimetric chemosensors for ion sensing

Novel colorimetric and fluorimetric chemosensors for F-, CN- and OH- containing anthraquinone and imidazole as signalling/binding sites have been synthesised and characterised. Upon addition of F-, CN- and OH- to acetonitrile solutions of compounds 1 and 2, a marked colour change from yellow to pink was observed and the fluorescence emission of 1 was switched on, whereas for 2 there was a fluorescence quenching. Considering recognition in organic aqueous mixture, it was found that selectivity for CN- was achieved for both receptors, with an easily detectable colour change from yellow to orange. Moreover, sensors 1 and 2 showed good sensitivity with mu M-level detection limit for cyanide in acetonitrile as well as in acetonitrile/water (9:1). Additionally, compounds 1 and 2 in their deprotonated form, after fluoride addition, were studied as metal ion chemosensors and displayed a drastic change from pink to yellow after metal ion complexation giving a yellow-pink-yellow, reversible colorimetric reaction and a on-off-on fluorescence in acetonitrile. The binding stoichiometry between the receptors and the anions and cations was found to be 1:1 and 2:1, respectively. The binding process was also followed by H-1 NMR titrations which corroborated the previous findings. (C) 2013 Elsevier B.V. All rights reserved,