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- Donovan, P., et al.
(författare)
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Unexpected Deformations Induced by Surface Interaction and Chiral Self-Assembly of Co-II-Tetraphenylporphyrin (Co-TPP) Adsorbed on Cu(110): A Combined STM and Periodic DFT Study
- 2010
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Ingår i: Chemistry - A European Journal. - : Wiley. - 1521-3765 .- 0947-6539. ; 16:38, s. 11641-11652
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Tidskriftsartikel (refereegranskat)abstract
- In a combined scanning tunnelling microscopy (STM) and periodic density functional theory (DFT) study, we present the first comprehensive picture of the energy costs and gains that drive the adsorption and chiral self-assembly of highly distorted Co-II-tetraphenylporphyrin (Co-TPP) conformers on the Cu(110) surface. Periodic, semi-local DFT calculations reveal a strong energetic preference for Co-TPP molecules to adsorb at the short-bridge site when organised within a domain. At this adsorption site, a substantial chemical interaction between the molecular core and the surface causes the porphyrin macrocycle to accommodate close to the surface and in a flat geometry, which induces considerable tilting distortions in the phenyl groups. Experimental STM images can be explained in terms of these conformational changes and adsorption-induced electronic effects. For the ordered structure we unambiguously show that the substantial energy gain from the molecule surface interaction recuperates the high cost of the induced molecular and surface deformations as compared with gas phase molecules. Conversely, singly adsorbed molecules prefer a long-bridge adsorption site and adopt a non-planar, saddle-shape conformation. By using a van der Waals density functional correction scheme, we found that the intermolecular pi-pi interactions make the distorted conformer more stable than the saddle conformer within the organic assembly. These interactions drive supramolecular assembly and also generate chiral expression in the system, pinning individual molecules in a propeller-like conformation and directing their assembly along non-symmetric directions that lead to the coexistence of mirror-image chiral domains. Our observations reveal that a strong macrocycle surface interaction can trigger and stabilise highly unexpected deformations of the molecular structure and thus substantially extend the range of chemistries possible within these systems.
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- Dyer, M. S., et al.
(författare)
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Understanding the Interaction of the Porphyrin Macrocycle to Reactive Metal Substrates: Structure, Bonding, and Adatom Capture
- 2011
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 5:3, s. 1831-1838
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the absorption and conformation of free-base porphines on Cu(110) using STM, reflection absorption infrared spectroscopy, and periodic DFT calculations in order to understand how the central polypyrrole macrocycle, common to all porphyrins, interacts with a reactive metal surface. We find that,the-macrocycle forms a chemisorption bond with the surface,, arising from electron donation into down-shifted, and nearly degenerate unoccupied porphine orbitals accompanied with electron back-donation from molecular pi-orbitals. Our calculations show that van der Waals interactions give rise to an overall Increase in the adsorption energy but only minor changes in the adsorption geometry and electronic structure. In addition, we observe copper adatoms being weakly attracted to adsorbed porphines at specific molecular sites. These results provide important insights into porphyrin-surface interactions that ultimately, will govern the design of robust surface mounted molecular devices based on this important class of molecules.
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