Self-assembly of molecules on surfaces directed by different supramolecular interactions has been widely explored. There are striking examples of molecular surface structures, whose formation is driven by dipolar coupling, metal coordination or hydrogen bonding. The latter two interactions are relevant for the self-assembled structures of the two perylene derivatives we analysed. Both were prepared on Cu(111) and analysed by STM and LEED.
The first perylene derivative (DPDI) is modified on the Cu-surface in order to achieve self-assemblies. This modification is thermally activated, thus providing an additional feature to the control of self-assemblies in contrast to usual approaches that make use of molecular properties already inherent to the molecules. Depending on the coverage before annealing, different H-bond assemblies can be generated, the most stable one being an open hexagonal network which is commensurate to the Cu(111) surface. [1]
For the second perylene derivative (TAPP) an open rectangular assembly is found on Cu(111). As well as for the first molecule (DPDI) LEED measurements show a commensurate unit cell. However, the assembly of TAPP differs from the one of DPDI in two aspects: An annealing step after the deposition of the molecule is not necessary for the formation of the network. Furthermore, the bonding mechanism is now based on a coordination bonding between the nitrogen atoms of TAPP and the copper atoms of the surface. For the analysis of the latter aspect TAPP was evaporated at sample temperatures below room temperature and the sample was stepwise annealed at different temperatures in order to study the formation of the open network in detail.
The evaporation of both molecules on the same sample and subsequent annealing leads to the separated formation of the networks mentioned above. This effect allows the creation of two templates that differ in form and dimension on the same sample only by means of self-assembly.
[1] M. Stöhr et al., Angew. Chem. Int. Ed., 44, 7394 (2005)
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