Stm Investigation Of Molecular Architectures Of Porphyrinoids On A Ag(111) Surface Supramolecular Ordering Electronic Properties And Reactivity 2010 Edition

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Springer Stm Investigation Of Molecular Architectures Of Porphyrinoids On A Ag(111) Surface Supramolecular Ordering Electronic Properties And Reactivity 2010 Edition by Florian Buchner

The functionalization of surfaces on the nanoscale is one of the most fascinating and at the same time challenging topics in science. It is the key to tailoring catalysts sensors or devices for solar energy conversion whose functional principle is based on the interaction of an active solid surface with another (liquid or gaseous) phase. As an example planar transition metal complexes adsorbed on solid supports are promising candidates for novel heterogeneous catalysts. An important feature of these catalysts compared to supported metal clusters is the fact that the active sites i. e. the coordinated metal centers with their vacant axial coordination sites are well de?ned and uniform. Metalloporphyrinoids are particularly suitable in this respect because they combine a structure forming element-the rigid molecular frame which often induces long range order-with an active site the coordinated metal ion. Its planar coordination environment leaves two axial coordination sites available for additional ligands. If adsorbed on a surface one of these axial sites is occupied by the underlying substrate. The resulting electronic interaction with the surface can be used to tailor the electronic structure and thereby the reactivity of the metal center. The remaining site is free for the attachment of molecules (sensor functionality) and/or operates as a reaction center (single-site catalysis). Prototype examples are omnipresent in nature where in particular metallo-tetrapyrrols play a decisive role in important biological processes with the most prominent examples being iron porphyrins in heme magnesium porphyrins in chlorophyll and cobalt corrin in vitamin B12. Table of contents : 1 Introduction ...................................................................................................... 12 Fundamentals .................................................................................................... 52.1 Principle of the STM ............................................................................................ 52.2 Origin of the Tunneling Current ........................................................................... 72.3 Scanning Tunneling Spectroscopy ...................................................................... 102.4 Contrast Mechanism of Molecular Adsorbates ................................................... 132.5 Temperature Programmed Desorption ................................................................ 162.6 Low Energy Electron Diffraction ....................................................................... 183 Experimental Setup ........................................................................................ 213.1 UHV System ...................................................................................................... 213.2 Scanning Tunneling Microscope ........................................................................ 233.3 Control Electronics and Vibration Isolation ........................................................ 263.4 Ag(111) ............................................................................................................. 283.5 Porphyrinoids..................................................................................................... 303.6 Preparation of thin Porphyrinoid Layers ............................................................. 333.7 Vapor-deposition of Cobalt and Iron .................................................................. 344 Results ............................................................................................................. 394.1 Self-Assembly and Individual Appearance of Tetraphenylporphyrins onAg(111) ............................................................................................................. 414.1.1 Epitaxial growth ........................................................................................... 434.1.2 Appearance and Intramolecular Conformation .............................................. 484.1.3 Ordering Aspects.......................................................................................... 504.2 Self-Assembly and Individual Appearance of Cobalt(II)-Tetrakisditertbutylphenylporphyrinson Ag(111) ......................................................................... 614.2.1 Polymorphism of CoTTBPP ......................................................................... 624.2.2 Polarity-Dependent Appearance ................................................................... 78ii Table of Contents4.3 Coordination of Iron and Cobalt Atoms by Tetraphenylporphyrin Monolayerson Ag(111) and Formation of Metal(II)-Tetraphenylporphyrin ......... 834.3.1 Coordination of Post-deposited Iron Atoms by TetraphenylporphyrinMonolayers ................................................................................................... 854.3.2 Coordination of Pre-deposited Iron Atoms by TetraphenylporphyrinMonolayers ................................................................................................... 904.3.3 Coordination of Post-deposited Cobalt Atoms by TetraphenylporphyrinMonolayers ................................................................................................... 944.3.4 Discussion of the Metalation Reaction .......................................................... 994.4 Different Aspects of 2H-Tetrakisditertbutylphenylporphyrin on Ag(111) .. 1034.4.1 Monolayer Preparation................................................................................ 1044.4.2 Arrangement of 2HTTBPP ......................................................................... 1074