Synthesis of electrochemical and optical anion sensors containing organic dyes

Abstract

Six chromo-and fluorogenic anion sensors have been synthesized by coupling the appropriate dithioisocyanate of anthracene derivatives with hexylamine in dichloromethane. The anthracene moieties acted as signaling units and thiourea moieties as binding sites. Anions binding properties of synthetic sensors have been studied by [superscript 1]H-NMR titration (10 mM in DMSO-d[subscript 6] and the 1:1 complexations were confirmed by Job's plots. Compounds L1 and L4 formed the most stable complexes with pimelate. Compounds L3 and L5 formed the most stable complexes with glutarate. Compound L2 formed the most stable complexes with succinate. Binding constants were, therefore, found to be strongly dependent on the chain length of dicarboxylate anions and the distance between thiourea groups. UV-vis titrations of all compounds (0.02 mM in DMSO) showed decreasing of maxima absorption intensity when successive addition of dicarboxylate anions. The log[beta]1 results indicated that compounds L1 formed the most stable complex with adipate. Compound L5 showed strongest binding abilities with oxalate as well as pimilate. However, compounds L2, L3, and L4 did not show must difference in binding abilities toward any anion. The complexation between compounds L1, L3 and L5 and anions were also studied by fluorescence titration and showed the decreasing of fluorescence emission upon successive addition of anions. The electrochemical studies of compounds L2 and L4 by cyclic voltammetry confirmed the occurring of complexation. The electrochemistry of compound L2 changed dramatically in the presence of succinate. The complexation between compound L4 and adipate showed the most significant change in cyclic voltammograms. Optimized structures of all conformers of the synthesized compounds and anion binding structures were obtained using density functional theory (DFT) and ONIOM methods.