title: Photoreduction of oxoisoaporphine dyes by amines: transient-absorption and semiempirical quantum-chemical studies.
abstract: Photoreduction by amines of oxoisoaporphine dyes occurs via a stepwise mechanism of electron-proton-electron transfer that leads to the metastable N-hydrogen oxoisoaporphine anion. During photoreduction that occurs from the triplet manifold of the oxoisoaporphine, a radical ion A(-)(*), a neutral-hydrogenated radical A-NH(*), and the metastable ion A-NH(-) of the oxoisoaporphine are formed. We present time-resolved spectroscopic data and quantum mechanical semiempirical PM3 and ZINDO/S results for the transient species formed during the flash photolysis of oxoisoaporphines in the presence of amines. These calculations reproduce adequately the experimental spectra of the triplet-triplet absorption near 450 nm, and that of neutral hydrogenated radical of the studied oxoisoaporphines centered at 390 nm. A transient absorption observed near 490 nm, for all of the studied systems, was explained by considering the formation of radical ion pair between the radical anion of the oxoisoaporphine, A(-)(*), and the radical cation of the amine, whose ZINDO/S calculated spectra generate the strongest transition near the experimentally observed absorption maximum at 490 nm, supporting the formation of a radical ion pair complex as the first step of the photoreduction.
authors.affiliation: Departamento de Química Organica y Fisicoquímica, Facultad de Ciencias Químicas y Farmacéuticas, Universidad de Chile, Casilla 233, Santiago 1, Santiago, Chile. jrfuente@ciq.uchile.cl
authors.forename: Julio R
authors.initials: JR
authors.lastname: De la Fuente
authors.forename: Verónica
authors.initials: V
authors.lastname: Neira
authors.forename: Claudio
authors.initials: C
authors.lastname: Saitz
authors.forename: Carolina
authors.initials: C
authors.lastname: Jullian
authors.forename: Eduardo
authors.initials: E
authors.lastname: Sobarzo-Sanchez