2D organisation of complex organic molecules

The self-assembly of two-dimensional molecular systems is of significant interest, offering an insight into the fundamental interactions which drive the formation of complex supramolecular structures. A careful choice of the molecular 'building blocks' for such self-assembled systems potentially allows the design and production of nanoscale architectures with pre-determined geometries and specific chemical functionalities. Within this thesis the two-dimensional structures formed by the self-assembly of complex organic molecules, deposited on an Au(111) surface held in an ultrahigh vacuum (URV) environment, are studied using a combination of scanning tunnelling microscopy (STM), photoelectron spectroscopy (PES), molecular dynamics (MD), and density functional theory (DFT) techniques. A UHV electrospray deposition (URV-ESD) technique is employed to facilitate the introduction of thermally labile molecules into the URV environment. Bi-molecular networks, formed from perylene tetracarboxylic diimide (PTCDI) and melamine, have previously been observed to assemble on the Au(111) surface. Several more complex phases are reported here, as characterised by S'I'M, with the balance between isotropic and anisotropic interactions giving rise to a variety of structures. Chemical functionality may be added to these networks by incorporating functionalised derivatives of PTCDI. Alternative structures produced by altering the shape of the molecular 'building blocks' are also discussed. The URV-ESD technique is demonstrated here to be compatible with the deposition of the fullerene C60,the single molecule magnet Mn12012(02CCR3h6(H20)4 (Mn12(acetate)16), and porphyrin based oligomers (P4 and P6) and polymers (Pn). The URV-ESD of C60on the clean AU(ll1) surface, and on a surface prepatterned with a PTCDI/melamine network, results in similar structures to those previously observed to be produced by sublimation. Mn12(acetate)16 and the porphyrin oligomers and polymers represent complex molecules which are thermally labile and possess, respectively, novel magnetic and electronic properties. Mn12(acetate) 16is observed to form filamentary aggregates due to the anisotropic nature of the molecule-molecule and molecule-substrate interactions, while P4, P6 and Pn form highly ordered close-packed domains driven by the interdigitation of the alkyl chains attached to the porphyrin cores. The findings presented within this thesis demonstrate that self-assembled molecular structures can be understood in terms of intermolecular interactions, and that for systems containing complex molecules the molecule-molecule interaction potential can lead to the formation of novel structures

Ullmann coupling reactions on Ag(111) and Ag(110); substrate influence on the formation of covalently coupled products and intermediate metal-organic structures Metal-Organic Structures

On-surface reactions based on Ullmann coupling are known to proceed on coinage-metal substrates (e.g. Au, Ag, Cu), with the chemistry of the surface strongly influencing the reaction progression. In addition, the topography of the surface may be expected to affect the local adsorption geometry of the reactants as well as the intermediate and final structures. Here, we investigate the effect of two different surface facets of silver, Ag(111) and Ag(110) on the formation of organometallic and covalent structures for Ullmann-type coupling reactions. Deposition of 4,4”-diiodo-m-terphenyl molecules onto either Ag(111) or Ag(110) surfaces leads to the scission of C-I bonds followed by the formation of organometalic zigzag structures, consisting of molecules connected by coordination bonds to Ag adatoms. The covalently coupled product is formed by annealing each surface, leading to the removal of Ag atoms and the formation of covalently bonded zigzag poly(m-phenylene) structures. Comparisons of the adsorption model of molecules on each surface before and after annealing reveal that on Ag(111), structures rearrange by rotation and elongation of bonds in order to become commensurate with the surface, whereas for the Ag(110) surface, the similarity in adsorption geometry of the intermediate and final states means that no rotation is required

Organisation and ordering of 1D porphyrin polymers synthesised by on-surface Glaser coupling

One-dimensional polymer chains consisting of π-conjugated porphyrin units are formed via Glaser coupling on a Ag(111) surface. Scanning probe microscopy reveals the covalent structure of the products and their ordering. The conformational flexibility within the chains is investigated via a comparision of room temperature and cryogenic measurements

Toward printing molecular nanostructures from microstructured samples in ultrahigh vacuum

Transferring molecular nanostructures from one surface to another in ultrahigh vacuum (UHV) by mechanical contact might be a possible route to avoid the severe limitations of in situ molecular synthesis on technologically relevant template surfaces. Here, transfer printing in UHV of molecular structures between metal surfaces is investigated by a combination of scanning tunneling microscopy and scanning electron microscopy/energy dispersive x-ray spectroscopy. The authors present the complete procedure of the printing and characterization process. Microstructured Au-coated MoS₂ samples exhibiting a periodic pillar structure are used as stamp surfaces with Au(111) single crystals as target surface. Polymers of 1,3,5-tris(4-bromophenyl)benzene molecules and graphene nanoribbons with an armchair edge structure are grown on the pillars of the stamp surface. After bringing the two surfaces in mechanical contact, the transferred material is found on the target while decapping occurs on the stamp surface. Polymer structures are probably buried under the transferred stamp material, and in rare cases, evidence for molecular structures is found in their vicinity

Ullmann coupling reactions on Ag(111) and Ag(110); substrate influence on the formation of covalently coupled products and intermediate metal-organic structures Metal-Organic Structures

On-surface reactions based on Ullmann coupling are known to proceed on coinage-metal substrates (e.g. Au, Ag, Cu), with the chemistry of the surface strongly influencing the reaction progression. In addition, the topography of the surface may be expected to affect the local adsorption geometry of the reactants as well as the intermediate and final structures. Here, we investigate the effect of two different surface facets of silver, Ag(111) and Ag(110) on the formation of organometallic and covalent structures for Ullmann-type coupling reactions. Deposition of 4,4”-diiodo-m-terphenyl molecules onto either Ag(111) or Ag(110) surfaces leads to the scission of C-I bonds followed by the formation of organometalic zigzag structures, consisting of molecules connected by coordination bonds to Ag adatoms. The covalently coupled product is formed by annealing each surface, leading to the removal of Ag atoms and the formation of covalently bonded zigzag poly(m-phenylene) structures. Comparisons of the adsorption model of molecules on each surface before and after annealing reveal that on Ag(111), structures rearrange by rotation and elongation of bonds in order to become commensurate with the surface, whereas for the Ag(110) surface, the similarity in adsorption geometry of the intermediate and final states means that no rotation is required

2D organisation of complex organic molecules

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

An on-surface reaction confined within a porous molecular template

On-surface reactions based on metal-catalysed Ullmann coupling have been successfully employed to synthesise a wide variety of covalently coupled structures. Substrate chemistry and topology are both known to effect the progression of an on-surface reaction; offering routes to control efficiency and selectivity. Here, we detail ultra-high vacuum scanning probe microscopy experiments showing that templating a catalytically active surface, via a supramolecular template, influences the reaction pathway of an onsurface Ullmann-type coupling reaction by inhibiting one potential intermediate structure and stabilising another

Oxytetracycline hydrochloride activity in honey bee larvae (Apis mellifera) following medication with various doses

Four replicated experiments were conducted to determine the concentration of oxytetracycline hydrochloride (OTC) in honey bee (Apis mellifera) larvae following application of the antibiotic to honey bee colonies. In the first experiment, the mean OTC concentration was significantly greater in whole larvae than in larval guts sampled from hives on the day immediately following treatment. In two further experiments, 0.3 g, 0.5 g and 1.0 g active OTC in caster sugar was administered to single- and double-storey colonies. The mean OTC concentration was above the minimum inhibitory concentration of OTC to Melissococcus pluton for 2 to 6 days post-treatment, depending upon the dose. The daily rate of change of concentration of OTC in larvae sampled from treated colonies ranged from 0.423 to 0.672. In a fourth experiment, application of 0.3 g and 0.5 g OTC in distilled water gave equal to or higher OTC levels in larvae on the first two days post-treatment when compared to the same doses applied in caster sugar

Bending a Photonic Wire into a Ring

Natural light harvesting systems absorb sunlight and transfer its energy to the reaction centre, where it is used for photosynthesis. Synthetic chromophore arrays provide useful models for understanding energy migration in these systems. Research has focussed on mimicking rings of chlorophyll molecules found in purple bacteria, known as ‘light-harvesting system 2’. Linear meso-meso linked porphyrin chains mediate rapid energy migration, but until now it has not been possible to bend them into rings. Here we show that oligo-pyridyl templates can be used to bend these rod-like photonic wires, to create covalent nanorings. The macrocycles consist of 24 porphyrin units, with a single butadiyne link. Their elliptical conformations have been probed by scanning tunnelling microscopy (STM). This system exhibits two types of excited state energy transfer processes: (a) from the central template to the peripheral porphyrins and (b) from the 24 light-absorbing porphyrin units to the π-conjugated butadiyne-linked porphyrin dimer segment