UV-vis and fluorescence spectroscopic detection of anions by the conformational restriction of 2,2′-binaphthalene derivatives bearing thiourea groups through a methylene spacer

Novel fluorescence receptors, 2 and 3 based on 2,2'-binaphthalene possessing thiourea moieties via a methylene spacer have been synthesized. Hydrogen bonds of NH groups of thiourea moieties with acetate anion were confirmed by H-1 NMR study in MeCN-d(3). These receptors showed characteristic UV-vis spectral changes through isosbestic points on complexation with anions inspite of lacking conjugation between the chromophore and the binding sites in polar organic solvent such as acetonitfile. The UV-vis spectral changes arise from the conformational restriction of the 2,2'-binaphthyl skeleton on the complexation. The receptors exhibit high selectivities for AcO- and F-. The fluorescence intensity of the receptors decreases with the increasing amount of the AcO-, however, addition of F- induces a different change in its fluorescence spectrum, in which shorter emission of the receptors decreases with the increase in F- concentration, while the longer emission of the receptors increases through an isoemissive point in MeCN. The results suggest that favorable dual-wavelength ratiometric fluorescence measurement can be conducted by the receptors for F-. (c) 2006 Elsevier Ltd. All rights reserved.