The fluorescence behaviour of 1,3-bis(8-quinolyloxy)propane derivatives and their analogues was investigated both in the presence and absence of alkali metal perchlorates in MeCN or MeOH. The fluorescence intensity increased significantly compared with that of the corresponding free carriers only on the addition of lithium perchlorate; sodium perchlorate had only a slight effect, and potassium perchlorate hardly and effect. It was found that the increase in the fluorescence intensity was proportional to the lithium concentration. Lithium ion can be detected quantitatively in MeCN in the concentration range 2 × 10^–6–10^–4 mol dm^–3 of lithium perchlorate, whereas in MeOH it can only be determined in the high concentration range (> 3 × 10^–2 mol dm^–3).