Chloride sensitive probes for biological applications

Three fluorescent probes have been produced by the quaternisation of 6-methylquinoline with methyl bromide, methyl iodide and 3-bromo-1-propanol. The probes are water-soluble and their fluorescence is quenched by modest concentrations of chloride ions. One of the dyes, dye 1, has a chloride Stern¯Volmer constant of 255 mol-1 dm3, which is one of the highest reported. Fluorescence quantum yields of the dyes have been determined using quinine sulphate as a reference and are all found to be similar lying in the range 0.5¯0.64. Applications for chloride determination in biological systems using these probes are discussed.