We describe a STM investigation of the structure and dynamics of alkylated thiotriphenylene monolayers at the solid–liquid interface. This discotic system was found to pack into two coexisting structural motifs on the basal plane of graphite. The interpretation of the intra-molecular contrast in the STM images showed a large contribution of electronic levels localized on the sulfur atoms bridging the conjugated core with the aliphatic side-chains. The temporal evolution of domain boundaries in a polycrystalline monolayer, explored by recording series of subsequent STM images, revealed an Ostwald ripening phenomenon, namely coarsening in two-dimensional molecular polycrystals.