Radical Ions of 3-Styryl-quinoxalin-2-one derivatives studied by pulse radiolysis in organic solvents
Author
dc.contributor.author
Skotnicki, Konrad
Author
dc.contributor.author
Fuente, Julio R. De la
Author
dc.contributor.author
Canete, Álvaro
Author
dc.contributor.author
Berrios, Eduardo
Author
dc.contributor.author
Bobrowski, Krzysztof
Admission date
dc.date.accessioned
2018-08-28T19:03:15Z
Available date
dc.date.available
2018-08-28T19:03:15Z
Publication date
dc.date.issued
2018
Cita de ítem
dc.identifier.citation
J. Phys. Chem. B 2018, 122, 4051−4066
es_ES
Identifier
dc.identifier.other
10.1021/acs.jpcb.8b01004
Identifier
dc.identifier.uri
https://repositorio.uchile.cl/handle/2250/151334
Abstract
dc.description.abstract
The absorption-spectral and kinetic behaviors of radical ions and neutral hydrogenated radicals of seven 3-styryl-quinoxalin-2(1 H)-one (3-SQ) derivatives, one without substituents in the styryl moiety, four others with electron-donating (R = -CH3, -OCH3, and -N(CH3)(2)) or electron-withdrawing (R = -OCF3) substituents in the para position in their benzene ring, and remaining two with double methoxy substituents (-OCH3), however, at different positions (meta/para and ortho/meta) have been studied by UV-vis spectrophotometric pulse radiolysis in neat acetonitrile saturated with argon (Ar) and oxygen (O-2) and in 2-propanol saturated with Ar, at room temperature. In acetonitrile solutions, the radical anions (4R-SQ(center dot-)) are characterized by two absorption maxima located at lambda(max) = 470-490 nm and lambda(max) = 510-540 nm, with the respective molar absorption coefficients epsilon(470-490) = 8500-13 100 M-1 cm(-1) and epsilon(510-540) = 6100-10 300 M-1 cm(-1), depending on the substituent (R). All 4R-SQ(center dot-) decay in acetonitrile via first-order kinetics, with the rate constants in the range (1.2-1.5) x 10(6) s(-1). In 2-propanol solutions, they decay predominantly through protonation by the solvent, forming neutral hydrogenated radicals (4R-SQH(center dot)), which are characterized by weak absorption bands with lambda(max) = 480-490 nm. Being oxygen-insensitive, the radical cations (4R-SQ(center dot+)) are characterized by a strong absorption with lambda(max) = 450-630 nm, depending on the substituent (R). They are formed in a charge-transfer reaction between a radical cation derived from acetonitrile (ACN(center dot+)) and substituted 3-styryl-quinoxalin-2-one derivatives (4R-SQ) with a pseudo-first-order rate constant k = (2.7-4.7) x 10(5) s(-1) measured in solutions containing 0.1 mM 4R-3-SQ. The Hammett equation plot gave a very small negative slope (rho = -0.08), indicating a very weak influence of the substituents in the benzene ring on the rate of charge-transfer reaction. The decay of 4R-SQ(center dot+) in Ar-saturated acetonitrile solutions occurs with a pseudo-first-order rate constant k = (1.6-6.2) x 10(4) s(-1) and, in principle, is not affected by the presence of O-2, suggesting charge-spin delocalization over the whole 3-SQ molecule. Most of the radiolytically generated transient spectra are reasonably well-reproduced by semiempirical PM3-ZINDO/S (for 4R-SQ(center dot-)) and density functional theory quantum mechanics calculations employing M06-2x hybrid functional together with the def2-TZVP basis set (for 4R-SQ(center dot+)).
es_ES
Patrocinador
dc.description.sponsorship
FONDECYT
1150567
Universidad de Chile
Polish National Center of Science (NCN) for PRELUDIUM grant
2014/15/N/ST4/02914
US Department of Energy Office of Science, Office of Basic Energy Science
DE-FC02-04ER15533