Luminescence excitation and de-excitation involving one-electron transfer

Abstract

The radiation-induced chemiluminescence (RCL) in aqueous solutions of 1-aminonaphthalene-4-(Na)sulphonate (AnsH) predominantly involves: AnsH·⁺+ e_aq→ 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·⁺+ HPO^2–₄⇌ 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.