title: Electron-transfer and acid-base properties of a two-electron oxidized form of quaterpyrrole that acts as both an electron donor and an acceptor.
abstract: Electron-transfer interconversion between the four-electron oxidized form of a quaterpyrrole (abbreviated as P4 for four pyrroles) and the two-electron oxidized form (P4H2) as well as between P4H2 and its fully reduced form (P4H4) bearing analogous substituents in the alpha- and beta-pyrrolic positions was studied by means of cyclic voltammetry and UV-visible spectroelectrochemistry combined with ESR and laser flash photolysis measurements. The two-electron oxidized form, P4H2, acts as both an electron donor and an electron acceptor. The radical cation (P4H2*+) and radical anion (P4H2*-) are both produced by photoinduced electron transfer from dimeric 1-benzyl-1,4-dihydronicotinamide to P4H2, whereas the cation radical form of the compound is also produced by electron-transfer oxidation of P4H2 with [Ru(bpy)3]3+. The ESR spectra of P4H2*+ and P4H2*- were recorded at low temperature and exhibit spin delocalization over all four pyrrole units. Thus, the two-electron oxidized form of the quaterpyrrole (P4H2) displays redox and electronic features analogous to those seen in the case of porphyrins and may be considered as a simple, open-chain model of this well-studied tetrapyrrolic macrocycle. The dynamics of deprotonation from P4H2*+ and disproportionation of P4H2 were examined by laser flash photolysis measurements of photoinduced electron-transfer oxidation and reduction of P4H2, respectively.
authors.affiliation: Department of Chemistry, University of Houston, Houston, Texas 77204-5003,USA.
authors.forename: Min
authors.initials: M
authors.lastname: Zhang
authors.forename: Wenbo
authors.initials: W
authors.lastname: E
authors.forename: Kei
authors.initials: K
authors.lastname: Ohkubo
authors.forename: David
authors.initials: D
authors.lastname: Sanchez-Garcia
authors.forename: Dae-Wi
authors.initials: DW
authors.lastname: Yoon
authors.forename: Jonathan L
authors.initials: JL
authors.lastname: Sessler
authors.forename: Shunichi
authors.initials: S
authors.lastname: Fukuzumi
authors.forename: Karl M
authors.initials: KM
authors.lastname: Kadish
mesh_terms: D000143:Acids / Q000737:chemistry*; D000468:Alkalies / Q000737:chemistry*; D004563:Electrochemistry; D004579:Electron Transport; D004583:Electrons; D006863:Hydrogen-Ion Concentration; D008752:Methylene Chloride / Q000737:chemistry; D008956:Models, Chemical; D015394:Molecular Structure; D010084:Oxidation-Reduction; D011758:Pyrroles / Q000737:chemistry*; D013997:Time Factors
chemical_list: D000143:Acids; D000468:Alkalies; D011758:Pyrroles; D008752:Methylene Chloride