Luminescence Excitation and De-excitation Involving One-electron Transfer Aqueous Solutions of l-Aminonaphthalene-4-(Na)sulphonate

Abstract

The radiation-induced chemiluminescence (RCL) in aqueous solutions of 1-aminonaphthalene-4-(Na)sulphonate (AnsH) predominantly involves: AnsH·++ eaq→ AnsH*. This conclusion is due to quantitative correlations found between the transient absorption, assigned to AnsH·+, and the RCL emission under various conditions modifying the AnsH·+ formation. Phosphates act on AnsH·+via the reaction: AnsH·++ HPO2–4⇌ Ans·+ H2PO–4. Azide radicals (·OH + N–3→ OH–+ N˙3) are about 7.5 times more efficient than ·OH in generating AnsH·+, at the expense of Ans· and AnsH·OH. Analogous phosphate and azide effects were found for a number of other efficient RCL compounds. Direct electron impact excitation of AnsH appears to occur 75 % by charge recombination. Halide type compounds are capable of perturbing this recombinational excitation process. Fluorescence quenching, on the other hand, is particularly efficient with electron-affinic compounds (A). A fairly good correlation was found between the fluorescence quenching rates k(AnsH*+ A) and the corresponding reaction rate constants k(e–aq+ A), suggesting that AnsH* de-excitation occurs by electron transfer to A. For ionic acceptors k(AnsH*+ A) depends upon the ionic strength of the solution.