Chemiluminescence of Succinylfluorescein and Related Compounds. I. Emitting Species Produced by the Reaction of Succinylfluorescein with Oxygen in Aprotic Solvents

In the course of our studies of the chemiluminescence of xanthene dyes, we found the violet chemiluminescence emission (CL-emission) resulting from the reaction of succinylfluorescein with oxygen in an aerated alkaline aqueous system of a high concentration of an aprotic solvent (DMSO or DMF), an especially intense emission occurring in aerated dry DMSO or DMF with tert-BuOK as base. The CL-emission comprised two emission components: an intense violet emission (a peak, at 410 nm) whose spectral distribution was similar to that of the fluorescence band which appeared during the course of the reaction, and a weak greenish-yellow emission similar to the fluorescence of the dye. By isolating and identifying the violet-fluorescent reaction product with an authentic sample, and by comparing the CL-emission with the fluorescence emission of the isolated product, it was concluded that the violet CL-emission may be attributed to the formation of an excited dianion of 3,6-dihydroxyxanthone. The reaction path leading to the dioxetane intermediate which will be produced by the elimination of a proton from the C atom at the β-position of the dye, followed by the oxygenation via the caged radical pair, was discussed as a likely mechanism for the formation of the excited dianion.