K W Hipps - A Self-Assembled Two-Dimensional Zwitterionic Structure: H6TSPP Studied on Graphite

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  Publication Details (including relevant citation   information):

  Friesen, Benjamin A., Wiggins, Bryan, McHale, Jeanne L., Mazur,   Ursula, Hipps, K. W. The Journal of Physical Chemistry C  2011 115 (10) 3990-3999

  Abstract: Well-defined monolayer islands of   protonated meso-tetrakis(4-sulfonatophenyl)porphine (H2[H4TSPP])   self-assembled on highly oriented pyrolytic graphite (HOPG) from   0.75 M HCl solutions are studied in ultrahigh vacuum using   scanning tunneling microscopy (STM), orbital-mediated tunneling   spectroscopy (OMTS), ultraviolet photoelectron spectroscopy   (UPS), and X-ray photoelectron spectroscopy (XPS). HOPG proved to   be a superior substrate because it does not form a thin surface   chloride in the presence of HCl, as does Au(111). Unlike   meso-tetrakis(4-carboxyphenyl)porphine (Hx[HyTCPP]), the   carboxylate analog, monolayers are stable on HOPG and can be   studied at room temperature without the addition of a second   stabilizing compound. Thus, the surface organizational energy for   H2[H4TSPP] is significantly stronger than that of Hx[HyTCPP].   This increased interaction is also apparent in the fact that the   H2[H4TSPP] monolayer has a much smaller unit cell. It is   suggested that sulfonate groups may be more useful than   carboxylates for creating self-assembled structures on HOPG.   Protonation of the porphyrin nitrogens in the surface species is   confirmed by XPS. High-resolution images of single molecule   layers show a well-defined deformation of the porphyrin ring, as   expected with complete protonation of the central nitrogen atoms.   OMTS and UPS were used to identify the **** and LUMO of the   H2[H4TSPP] monolayer species, and results are contrasted to those   of nickel(II) tetraphenylporphyrin (NiTPP). H2[H4TSPP] previously   has been shown to form well-defined nanorods on HOPG. I−V curves   of single and stacked rods taken by STM are consistent with   conduction in a band formed from the LUMO of H2[H4TSPP].

  Address (URL): http://dx.doi.org/10.1021/jp112086p