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Atomic-Resolution Kinked Structure of an Alkylporphyrin on Highly Ordered Pyrolytic Graphite
Yiing Chin1, Dwi Panduwinata1, Maxine Sintic1
1†School of Chemistry, The University of Sydney, NSW 2006, Australia.
Abstract:
The atomic structure of the chains of an alkyl porphyrin (5,10,15,20-tetranonadecylporphyrin) self-assembled monolayer (SAM) at the solid/liquid interface of highly ordered pyrolytic graphite (HOPG) and 1-phenyloctane is resolved using calibrated scanning tunneling microscopy (STM), density functional theory (DFT) image simulations, and ONIOM-based geometry optimizations. While atomic structures are often readily determined for porphyrin SAMs, the determination of the structure of alkyl-chain connections has not previously been possible. A graphical calibration procedure is introduced, allowing accurate observation of SAM lattice parameters, and, of the many possible atomic structures modeled, only the lowest-energy structure obtained was found to predict the observed lattice parameters and image topography. Hydrogen atoms are shown to provide the conduit for the tunneling current through the alkyl chains.
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