title: Inner-sphere electron-transfer reorganization energies of zinc porphyrins.
abstract: Inner-sphere electron-transfer reorganization energies of Zn(protoporphyrin IX) and Zn(octaethylporphyrin) are determined from band-shape analyses of the first ionization obtained by gas-phase valence photoelectron spectroscopy. The experimentally determined total inner-sphere reorganization energies for self-exchange (120-140 meV) indicate that structural changes upon oxidation are largely confined to the porphyrin ring, and substituents on the ring or solvent and other environmental factors make smaller contributions. Computational estimates by different models vary over a wide range and are sensitive to numerical precision factors for these low reorganization energies. Of current computational models that are widely available and practical for molecules of this size, functionals that contain a mixture of Hartree-Fock exchange and DFT exchange-correlation appear to be the most applicable.
authors.affiliation: Division of Chemistry and Chemical Engineering and the Beckman Institute, California Institute of Technology, Pasadena, CA 91125, USA.
authors.forename: Xenia
authors.initials: X
authors.lastname: Amashukeli
authors.forename: Nadine E
authors.initials: NE
authors.lastname: Gruhn
authors.forename: Dennis L
authors.initials: DL
authors.lastname: Lichtenberger
authors.forename: Jay R
authors.initials: JR
authors.lastname: Winkler
authors.forename: Harry B
authors.initials: HB
authors.lastname: Gray
mesh_terms: D008665:Metalloporphyrins / Q000737:chemistry*; D008956:Models, Chemical; D011166:Porphyrins / Q000737:chemistry*; D011524:Protoporphyrins / Q000737:chemistry*; D013057:Spectrum Analysis / Q000379:methods; D013816:Thermodynamics; D015032:Zinc / Q000737:chemistry*
chemical_list: D008665:Metalloporphyrins; D011166:Porphyrins; D011524:Protoporphyrins; C488938:octaethylporphyrin; C028025:protoporphyrin IX; D015032:Zinc