We described the two-dimensional (2D) assemblies of N,N'-dialkyl-substituted quinacridone derivatives on highly orientated pyrolytic graphite (HOPG) observed by scanning tunneling microscopy (STM), and focused on how minor structural variations can influence the supramolecular organization of the compounds. For quinacridone derivatives with or without methyl groups only the same enantiotopic faces of the quinacridone cores are observed with high resolution depending on the length of the substituted alkyl chains. For coadsorptions of quinacridone derivatives and fatty acids at the liquid/graphite interface, we have found interestingly that quinacridone derivatives with rnethyl groups form chiral racemates, whereas the quinacridone derivative without methyl groups forms chiral domains. The chiral 2D structures formed at the interface are only observed when fatty acids are present as guest molecules and for quinacridone derivatives substituted with long alkyl chains, -C22H45. These findings suggest that the 2D nanopatterned structure of quinacridone derivatives with light-emitting properties can be adjusted by controlling intermolecular interaction through tailor-made molecular building blocks and coadsorption.