Electron Spin Resonance Study on Radical Anions of Acridine and Its Halogen Derivatives

Abstract

Abstract ESR spectra of radical anions produced by bringing 9-chloro-, 2,7-dibromo-9-chloro-, and 2,4,5,7-tetrabromo-9-chloroacridine into contact with alkali metal (sodium and potassium) in tetrahydrofuran were measured at room temperature and/or at lower temperatures, and the analysis of them was made by means of a simulation method. Hyperfine coupling constants of acridine anion radicals, produced by the similar method in tetrahydrofuran and also by the electrolytic reduction in acetonitrile with the flow method, were determined, taking those of halogen derivatives into consideration. ESR spectra of acridine and 9-chloroacridine anion radical were found to involve the coupling of sodium, showing that these radicals were in the form of ion pair. The coupling constants of bromoacridine anion radicals did not give any difference between the sodium and the potassium reduction. The couplings of halogen atoms were not observed. Good agreement was obtained between the coupling constants calculated from spin densities and those determined experimentally. In general, the solution of radical anions of halogenides gradually yields brownish aggregates at lower temperatures (−20∼–30°C), their ESR spectra becoming weaker and unresolved. The temperature change is reversible and qualitatively resembles the behavior of acridine anion radical.