Influence of molecular–substrate interaction on the self-assembly of discotic liquid crystals

We compare by scanning tunnelling microscopy the structure of hexakis-2,3,6,7,10,11-alkyloxytriphenylene self-assembled at the liquid–solid interface with either gold (1 1 1) or graphite (HOPG) as the substrate. The symmetry-breaking transition previously observed on graphite, when the length of the side-chains is increased, is observed to take place also on gold. However, it corresponds to a more drastic reduction of symmetry and is associated to a decrease of the molecular area. We interpret this change in terms of a variation in the adsorption energy of the conjugated core with the substrate.