title: Probing surface-porphyrazine reduction potentials by molecular design.
abstract: This manuscript reports electrochemical and angle-resolved X-ray photoelectron spectroscopy measurements of surface-bound porphyrazine monolayers in which the molecule-surface distance and molecular orientation of the porphyrazine are controlled through the design of the adsorbates. This system has allowed us to probe the importance of molecule-surface interaction in determining the shift in reduction potential upon binding to a gold surface. This quantity currently is in theoretical dispute, with one computation indicating that a porphyrazine/porphyrin exhibits an extremely large covalent binding energy ( approximately 10 eV) to a gold surface, whereas a more recent one finds the binding energy to be only a fraction of an electronvolt. Our study indicates that the shift in reduction potential upon surface binding is not a discontinuous function of the molecule-surface distance, as would be the case if covalent interaction of the porphyrazine core with the gold surface were controlling, but rather varies smoothly. This, therefore, rules out the possibility that the large potential shift seen for a porphyrazine whose macrocyclic core lies approximately 3.9 A above the gold surface, relative to one that lies approximately 8.9 A above the surface, DeltaDeltaE = 340 mV, is caused by direct covalent binding of the pi-system to the metal surface.
authors.affiliation: Department of Chemistry and International Institute for Nanotechnology, Northwestern University, Evanston, IL 60208, USA.
authors.forename: Peng
authors.initials: P
authors.lastname: Sun
authors.forename: Hong
authors.initials: H
authors.lastname: Zong
authors.forename: Khalid
authors.initials: K
authors.lastname: Salaita
authors.forename: Jacob B
authors.initials: JB
authors.lastname: Ketter
authors.forename: Anthony G M
authors.initials: AG
authors.lastname: Barrett
authors.forename: Brian M
authors.initials: BM
authors.lastname: Hoffman
authors.forename: Chad A
authors.initials: CA
authors.lastname: Mirkin
mesh_terms: D004563:Electrochemistry / Q000379:methods*; D004566:Electrodes; D004583:Electrons; D006046:Gold / Q000737:chemistry; D008665:Metalloporphyrins / Q000737:chemistry*; D008956:Models, Chemical; D008968:Molecular Conformation; D011166:Porphyrins / Q000737:chemistry; D013052:Spectrometry, X-Ray Emission; D013499:Surface Properties; D013816:Thermodynamics
chemical_list: D008665:Metalloporphyrins; D011166:Porphyrins; D006046:Gold