Transient Phenomena in the Pulse Radiolysis of Oxoisoaporphine Derivatives in Acetonitrile

Abstract

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 lambda(max) = 605 and 590 nm, with molar absorption coefficients epsilon(605) = 5600 M-1 cm(-1) and epsilon(590) = 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) x 10(5) 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 lambda(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 lambda(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, 109, 5897). Most of the transient spectra generated radiolytically are adequately reproduced by quantum mechanical semiempirical PM3 and ZINDO/S methods.