The influence of perchlorates on the fluorescence quenching of 9,10-dichloroanthracene by bromide salts in acetone

Fluorescence quenching of 9,10-dichloroanthracene by lithium bromide and tetra-n-butylammonium bromide in acetone has been investigated in the presence of perchlorate salts. In the presence of LiBr, the Stern–Volmer (S–V) plots exhibit downward curvatures indicating that two species are responsible for the quenching process, namely free bromide anions and lithium bromide ion pairs. The addition of a perchlorate salt modifies the S–V dependencies due to the influence of perchlorates on the degree of lithium bromide dissociation. The association constant of lithium bromide has been determined by conductivity measurements and it agrees well with the estimates made from the fluorescence quenching measurements. The mechanism of fluorescence quenching by lithium bromide is discussed on the basis of electron transfer and the heavy-atom effect.