title: Formal hydride transfer mechanism for photoreduction of 3-phenylquinoxalin-2-ones by amines. Association Of 3-phenylquinoxalin-2-one with aliphatic amines
abstract: The photophysical and photochemical behavior of 1-methyl-3-phenylquinoxalin-2-one (MeNQ) and 3-phenylquinoxalin-2-one (HNQ) in the presence of amines is reported. While HNQ fluorescence shows an auxochromic effect and a bathochromic shift with added amines, explained by association of HNQ with amine in the ground state and emission from both excited species HNQ and [HNQ-amine], both MeNQ and HNQ are photoreduced efficiently on irradiation in the presence of amines, leading to the semireduced quinoxalin-2-ones, MeNQH(-) and HNQH(-), respectively, via an electron-proton-electron transfer, with unit quantum yields at high amine concentrations. The semireduced quinoxalin-2-ones XNQH(-) (X = H, Me) revert almost quantitatively to the parent XNQ in a dark thermal reaction with an activation free energy for MeNQH(-) of 17.4 and 25.9 kcal/mol in acetonitrile and benzene, respectively. Kinetic and spectroscopic (UV and NMR) evidence supports the proposed reaction mechanism for the reversible photoreduction.
authors.affiliation: Departamento de Quimica Organica y Fisicoquimica, Facultad de Ciencias Quimicas y Farmaceuticas, Universidad de Chile, PO Box 233, Santiago 1, Santiago, Chile.
authors.forename: J R
authors.initials: JR
authors.lastname: De La Fuente
authors.forename: A
authors.initials: A
authors.lastname: Canete
authors.forename: A L
authors.initials: AL
authors.lastname: Zanocco
authors.forename: C
authors.initials: C
authors.lastname: Saitz
authors.forename: C
authors.initials: C
authors.lastname: Jullian