Tailor-made molecules for the functionalisation of electrodes : from tripodal complexes to thioketal compounds

The scope of the present PhD thesis is the synthesis and characterization of new functional molecules purposely designed for studies on metal surfaces and possible use in molecular electronics. A special focus is set on the combination of certain chemical and structural functionalities of electronically active molecules. Thus specific properties and increased stability on the surface can be generated. In this regard we designed and synthesized different classes of compounds to adjust to the desired properties.
The first class is based on organic tripodal scaffolds adapted for metal coordination and their subsequent deposition on a metallic surface. The structures are functionalized with sulphur-containing terminal ends (thiomethyl and thioacetyl groups) or pyridine units as anchoring groups. Multipodal adsorption of the tripod is expected to provide self-standing wires on the surface for electron transport investigation at single molecule level without the influence or support of surrounding molecules. The variation of the organic structure, anchoring groups, metal ions and counter ions allows for comparative studies in the electron transport behaviour predefined by the respective targets. Preliminary studies by STM measurements on Au(111) of two of the series of metal complexes have been addressed by deposition in “sub-monolayer” concentrations and present the first results of these types of complexes at single molecule level.
The second class is based on homobimetallic helical complexes considered as molecular metal wires, functionalized with sulphur-containing anchoring groups. The structures investigated so far can be envisioned as a connection of two tripodal structures with anchoring groups on both ends. The use of different metal ions offers a variation of magnetic behaviour by which the electron transport properties are expected to be modulated.
The third class of compounds reports new series of chiral ligands and their Zn(II)-complexes based on the optically active binaphthyl motif as potential chiral materials for optoelectronic devices. The synthetic introduction of different substituents in different positions on the Schiff base phenoxy moiety is designed in order to tune their properties and applications such as electropolymerization and surface attachment for electron transport studies.
The fourth class concentrates on the synthesis of molecules containing charged moieties which are equipped with thioketal functional groups. The structural variation of the charged molecule and the corresponding neutral analogues allow for a comparative study on a metallic surface. The thioketal functionality is expected to offer a more stable anchoring facility to the surface by the two sulphur atoms. Thus it is proposed as new anchoring group for electronic transport investigation on gold surfaces.