Functional optimization by control of the electronic and structural properties of organic molecules on surfaces studied by scanning tunnelling microscopy

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The electronic and optical properties of molecular devices such as Organic Field Effect Transistors (OFETs), Solar Cells and molecular switches critically depend on the intermolecular interaction with their direct neighbors as well as the molecule-substrate interaction occurring in surface assisted thin organic film systems. The optimization of the different types of interplay occurring in complex functional molecular systems requires detailed theoretical understanding and rational design of the molecular structure. A systematic approach of the investigation of hierarchical systems starts from single molecules on solid substrates, and will include 2D molecular self-assemblies with controllable van der Waals- and coordination bonding, and finally covalent bonding, the latter allowing to generate stable systems under ambient conditions. Here, we will focus on the functional optimization by control of the electronic and structural properties of selected molecular systems. On the single molecule level we will study the functionality of single molecules such as metal coordinated macrocycles by LT-STM/STS. In this context phenantrene derivatives will be investigated with respect to their pinning capabilities for light chemical elements (H) and new metal coordination bond formation capabilities. With respect to complex pattern formation of monomeric systems we will investigate close packed layers in particular with respect to their orientation order-disorder behavior as discovered recently in our STM lab at WWU by controlling systematically the interplay of the intermolecular (e.g. van der Waals) interaction and the competing molecule-substrate interaction. Finally, covalent 2D-molecular network forming layers based on six-fold multidentate molecules will be investigated in view of their potential for the generation of thermoelectric and photo-responsive systems. Complementary to these experimental studies, systematic theoretical investigations will be performed to understand in detail the influence of molecule-substrate and intermolecular interactions as well as the electronic and optical properties of the studied systems as a basis for optimization and developing new control schemes for functional molecular self-assemblies.