Temperature dependence of conformation, chemical state, and metal-directed assembly of tetrapyridyl-porphyrin on Cu(111).
We present a combined scanning tunneling microscopy (STM), near-edge x-ray-absorption fine-structure, and x-ray photoemission spectroscopy (XPS) study on the bonding and ordering of tetrapyridyl-porphyrin molecules on the Cu(111) surface in the 300-500 K temperature range. Following deposition at 300 K the molecules are adsorbed with a pronounced conformational adaptation of the anchored species featuring a saddle-shaped macrocycle and terminal groups pointing toward the substrate. Upon moderate annealing supramolecular chains evolve that are stabilized by metal-ligand interactions between the mesopyridyl substituents and copper adatoms resulting in twofold copper coordination. Annealing to temperatures exceeding 450 K strongly alters the molecular appearance in high-resolution STM data. This modification was also induced by controlled voltage pulses and related to a deprotonation of the molecule by XPS. Under appropriate conditions a novel binding motif leads to honeycomb structures coexisting with the chain segments. The conformation withstands annealing without large modification.
Klappenberger
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Physik Department E20, Technische Universitat Munchen, James-Franck Str., D-85748 Garching, Germany. florian.klappenberger@ph.tum.de
Weber-Bargioni
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Auwärter
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Marschall
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Schiffrin
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Barth
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