New indolium and quinolinium dyes sensitive to aqueous halide ions at physiological concentrations

Twelve new highly fluorescent dyes have been produced by the reaction of two heterocyclic nitrogen bases with 8-bromooctanoic acid, 11-bromoundecanoic acid and 15-bromopentadecanoic acid. The bromide counter ions of the first six dyes have been replaced with the tetraphenylborate ion. 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 dyes 1-12 are reduced in the presence of aqueous halide ions allowing halide concentrations to be determined accurately at physiological levels. All the dyes have been characterised in terms of steady state fluorescence spectra and steady-state Stem-Volmer analysis.