Browsing by Author "Duncan, David A."

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Citation - WoS: 16
Dynamics of Spatially Confined Bisphenol a Trimers in a Unimolecular Network on Ag(111)
(Amer Chemical Soc, 2016) Lloyd, Julian A.; Papageorgiou, Anthoula C.; Fischer, Sybille; Oh, Seung Cheol; Saglam, Ozge; Diller, Katharina; Duncan, David A.
Bisphenol A (BPA) aggregates on Ag(111) shows a polymorphism between two supramolecular motifs leading to formation of distinct networks depending on thermal energy. With rising temperature a dimeric pairing scheme reversibly converts into a trimeric motif, which forms a hexagonal superstructure with complex dynamic characteristics. The trimeric arrangements notably organize spontaneously into a self-assembled one-component array with supramolecular BPA rotors embedded in a two-dimensional stator sublattice. By varying the temperature, the speed of the rotors can be controlled as monitored by direct visualization. A combination of scanning tunneling microscopy and dispersion corrected density-functional tight-binding (DFTB-vdW(surf)) based molecular modeling reveals the exact atomistic position of each molecule within the assembly as well as the driving force for the formation of the supramolecular rotors.
Citation - WoS: 11
Citation - Scopus: 11
Isomerism Control of Diethylstilbestrol by Metal Surface Induced O-H Cleavage
(Royal Soc Chemistry, 2018) Oh, Seung Cheol; Lloyd, Julian A.; Fischer, Sybille; Saglam, OEzge; Papageorgiou, Anthoula C.; Diller, Katharina; Duncan, David A.
Diethylstilbestrol (DES) is studied on Ag(111) and Cu(111) surfaces using X-ray photoelectron spectroscopy (XPS) and scanning tunnelling microscopy (STM). We find that DES molecules on the silver surface adsorb intact and adopt a trans-conformation. On the more reactive copper surface, O-H bond cleavage results in molecular adsorption in the cis-conformation, thus providing the means of obtaining different adsorption geometries. The difference in isomerism is reflected in the observed self-assemblies which exhibit room-temperature stability.
Citation - WoS: 50
Citation - Scopus: 54
Synthesis of Pyrene-Fused Pyrazaacenes on Metal Surfaces: Toward One-Dimensional Conjugated Nanostructures
(Amer Chemical Soc, 2016) Jiang, Li; Papageorgiou, Anthoula C.; Oh, Seung Cheol; Sağlam, Özge; Reichert, Joachim; Duncan, David A.; Zhang, Yi-Qi
We investigated the synthesis of one-dimensional nanostructures via Schiff base (imine) formation on three close-packed coinage metal (Au, Ag, and Cu) surfaces under ultrahigh vacuum conditions. We demonstrate the feasibility of forming pyrene-fused pyrazaacene-based oligomers on the Ag(111) surface by thermal annealing of tetraketone and tetraamine molecules, which were designed to afford cyclocondensation products. Direct visualization by scanning tunneling microscopy of reactants, intermediates, and products with submolecular resolution and the analysis' of their statistical distribution in dependence of stoichiometry and annealing temperature together with the inspection of complementary X-ray photoelectron spectroscopy signatures provide unique insight in the reaction mechanism, its limitations, and the role of the supporting substrate. In contrast to the reaction on Ag(111), the reactants desorb from the Au(111) surface before reacting, whereas they decompose on the Cu(111) Surface during the relevant thermal treatment.