Transient phenomena in the pulse radiolysis of oxoisoaporphine derivatives in acetonitrile

The absorption-spectral and kinetic behavior of radical ions and triplet states of two oxoisoaporphine derivatives, 2,3-dihydrooxoisoaporphine (2,3-DHOA) and 5-methoxy-2,3-dihydrooxoisoaporphine (5-MeO-2,3-DHOA), have been studied by UV-vis spectrophotometric pulse radiolysis in a neat acetonitrile saturated with argon and oxygen at room temperature. The radical anions of 2,3-DHOA and 5-MeO-2,3-DHOA are characterized by intense absorption maxima located at λ_max = 605 and 590 nm, with molar absorption coefficients ε₆₀₅ = 5600 M^-1 cm^-1 and ε₅₉₀ = 4900 M^-1 cm^-1, respectively. Both radical anions decay via first-order kinetics with the rate constants in the range (1.5-2.6) × 10⁵ s^-1, predominantly through protonation by adventitious water forming neutral-hydrogenated radicals. Oxygen insensitive, the radical cations of 2,3-DHOA are characterized by a strong nondescript absorption band with no distinct λ_max in the range 350-450 nm. On the other hand, the radical cations of 5-MeO-2,3-DHOA are characterized by the distinctive absorption band with λ_max = 420 nm. The experimental spectra of the neutral-hydrogenated radicals and the triplet excited states derived from 2,3-DHOA and 5-MeO-2,3-DHOA are in accordance with the spectra observed previously during laser flash photolysis (De la Fuente, J. R.; et al. J. Phys. Chem. 2005, 709,5897). Most of the transient spectra generated radiolytically are adequately reproduced by quantum mechanical semiempirical PM3 and ZINDO/S methods.