Lucigenin radical cation

ESR spectroscopy, however, revealed that 75, which one may call a ketyl radical, was not present in alkaline solutions of 77 in absence of oxidizing agents. The signal actually observed was that of 9-hydroxy-N,N -dimethyl-9,9 -biacridan radical 76. It was suggested that this radical was formed by one-electron transfer from N-methyl-acridone radical anion 75 to lucigenin monocarbinol 77, or by addition of hydroxide ion to lucigenin radical cation 78 (formed from lucigenin by one-electron transfer by the ketyl 75). 

Several lucigenin byproducts were identified, and ESR (at pH 13) demonstrated the presence of radicals formed independently of the presence of oxygen. Such signals disappeared rapidly on the addition of H2O2. Reaction of O2 with the lucigenin radical cation (i. e. lucigenin plus one electron) apparently gave N-methyl acridone. 

Legg and Hercules have shown that the reaction of superoxide with lucigenin results in chemiluminescence. A similar conclusion was reached by Fridovich and coworkers, who observed chemiluminescence upon the addition of lucigenin to the xanthine-xanthine oxidase system, which is known to produce 02 . In order to emit chemiluminescence, lucigenin must first be reduced by one electron to produce the radical cation 43 (Scheme 30). This species reacts with superoxide ion, producing the intermediate 1,2-dioxetane, whose decomposition is responsible for luminescence. ... 

On photoreduction of 9,9 -biacridine in ethanol, Niizuma et al. obtained the radical-cation 91 (R = H) and analyzed its ESR spectrum.319 The corresponding radical 91 (R = Me) has been prepared by electron transfer from carbanions to lucigenin.260 Its ESR spectrum has been analyzed by Janzen and co-workers.259... 

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