Behaviour of 2,9-disubstituted 1, 10-phenanthroline derivatives as specific lithium ion fluorophores

Abstract

1, 10-Phenanthroline derivatives having butyl groups at positions 2 and 9 were found to exhibit a marked increase in fluorescence intensity in organic solvents such as acetonitrile and 1,4-dioxane in the presence of lithium perchlorate, but not in the presence of sodium, potassium and beryllium ions. The fluorescence intensity depends largely on the nature of the substituents at positions 2 and 9; the enhancement of the fluorescence intensity is relatively small for the 2, 9-dimethyl derivatives and is virtually negligible for the 2,9-di-tert-butyle derivatives. In contrast, the nature of the substituents at positions 4 and 7 has very little effect on the fluorescence intensity. The concentration of lithium ions has a significant effect on the fluorescence spectrum; the fluorescence intensity varies markedly with the lithium ion concentration in the range from 1 × 10^–6 to 1 × 10^–4 mol dm^–3. It is suggested that these phenanthroline derivatives might be applied to the selective spectrofluorimetric detection of lithium ions. The effect of solvents on the fluorescence intensity was also investigated. It was found that acetonitrile and 1,4-dioxane increased the fluorescence intensity markedly.