New fluorescent indolium and quinolinium dyes for applications in aqueous halide sensing

Abstract

Bromide and teraphenylborate salts of six new highly fluorescent dyes, produced by the reaction of two heterocyclic nitrogen bases with 8-bromo-octanoic acid, 11-bromo-undecanoic acid and 15-bromo-pentadecanoic acid have been prepared. Unlike the bases themselves, the quaternary salts are water soluble and have fluorescence characteristics independent of pH in the pH range 7–11. Both the fluorescence intensity and fluorescence lifetime of these dyes are reduced in the presence of aqueous halide ions, allowing halide concentrations to be determined accurately at concentrations of importance to both medicine and industry. All the dyes have been characterised in terms of steady state fluorescence spectra and steady-state Stern-Volmer analysis. The Stern–Volmer constants, ( K SV), for the dyes are compared to those obtained for some commercially available dyes. The prospects for using these dyes in halide sensor devices are discussed.