Substrate-Induced Varied Conformation and Molecular Assemblies: In Situ STM Observation of β-Substituted Oligothiophene Adlayers on Au(111)

The adsorption of 3,3′′′-dihexyl-2,2′:5′,2′′:5′′,2′′′-quaterthiophene (4T) molecules on an Au(111) electrode was examined by using in situ scanning tunneling microscopy in 0.10 M HClO4, revealing internal molecular structures of the tetrathiophene backbones and the hexyl side chains. The 4T admolecules were packed in lamellae with their molecular axis aligned along the main axis of the Au(111) substrate and their hexyl side chains interdigitated to enhance intermolecular interaction. Dynamics of molecular organization incurred by the shifting of potential was also observed in this study. By examining and comparing the adsorption of 4T on HOPG and Au(111), we address the role of the substrate in understanding the arrangement of 4T admolecules.