期刊
ACS NANO
卷 7, 期 4, 页码 3139-3149出版社
AMER CHEMICAL SOC
DOI: 10.1021/nn305487c
关键词
porphyrin; porphine; repulsion; self-assembly; scanning tunneling microscopy; near-edge X-ray absorption fine structure; interface; photoelectron spectroscopy; charge transfer
类别
资金
- ERC [247299]
- German Research Foundation (DFG) [BA 3395/2-1]
- Munich Center for Advanced Photonics (MAP)
- Technische Universitat Munchen
- Institute for Advanced Study
- German Excellence Initiative
- Marie Curie Intra-European Fellowship [274842]
We investigated the surface bonding and ordering of free-base porphine (2H-P), the parent compound of all porphyrins, on a smooth noble metal support. Our multitechnique investigation reveals a surprisingly rich and complex behavior, induding intramolecular proton switching, repulsive intermolecular interactions, and density-driven phase transformations. For small concentrations, molecular-level observations using low-temperature scanning tunneling microscopy dearly show the operation of repulsive interactions between 2H-P molecules in direct contact with the employed Ag(111) surface, preventing the formation of islands. An increase of the molecular coverage results in a continuous decrease of the average intermolecular distance, correlated with multiple phase transformations: the system evolves from an isotropic, gas-like configuration via a fluid-like phase to a crystalline structure, which finally gives way to a disordered layer. Herein, considerable site-specific molecule substrate interactions, favoring an exclusive adsorption on bridge positions of the Ag(111) lattice, play an important role. Accordingly, the 2D assembly of 2H-P/Ag(111) layers is dictated by the balance between adsorption energy maximization while retaining a single adsorption site counteracted by the repulsive molecule molecule interactions. The long-range repulsion is associated with a charge redistribution at the 2H-P/Ag(111) interface comprising a partial filling of the lowest unoccupied molecular orbital, resulting in long-range electrostatic interactions between the adsorbates. Indeed, 2H-P molecules in the second layer that are electronically only weakly coupled to the Ag substrate show no repulsive behavior, but form dense-packed islands.
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