Self-Assembly of Benzodithiophene Derivatives on Graphite: Effects of Substitution Alkoxy Chain Number and Location

Self-assembling of polycyclic benzodithiophene derivatives (PBDs), a family of important optoelectronic organic molecules, at highly oriented pyrolytic graphite was studied with scanning tunneling microscopy. The experimental results showed that variation of the attached alkoxy chain number caused drastic structural changes of the corresponding assemblies. The competitions between the pi-conjugated cores and the alkoxy chains led to the structural transformations from relatively compact core-induced line patterns to more open chain-induced networks. Furthermore, the substitution location of the attached alkoxy chain in the PBD molecules also played an important role in tuning the molecular conformations in the two-dimensional self-assembled monolayers. Thermally induced transformation from energetically unfavorable structures to thermodynamically favorable ones was also observed. The changes of the self-assembling structures of the PBDs due to the variation of the attached alkoxy chain number may help in understanding the optoelectronic properties of the organic field-effect transistors made of the alkoxylated PBD molecules.