In Situ Scanning Tunneling Microscopic Investigation of the Two-Dimensional Ordering of Different Alkyl Chain-Substituted Quinacridone Derivatives at Highly Oriented Pyrolytic Graphite/Solution Interface

Adlayers of N-alkyl-substituted quinacridone derivatives have been imaged at highly oriented pyrolytic graphite (HOPG)/solution interfaces by scanning tunneling microscopy (STM). The quinacridone derivatives bearing long alkyl chains form stripe patterns, which are attributed to the physisorption induced by the HOPG surface. The well-resolved alkyl chains suggest relatively high stability and ideal packing of the long chains on the graphite surface. For derivatives bearing short alkyl chains, a grainlike structure is formed, but alkyl chains are not resolved. When quinacridone derivatives bearing long and short alkyl chains are mixed, a hexagon honeycomb structure is observed as a transition state. However, this transition state is not stable and it separates out spontaneously to form the two above-mentioned stable domain structures for long and short alkyl chains.