Structural and Electronic Properties of Thiophene-Based Supramolecular Architectures: Influence of the Underlying Metal Surfaces

Dicyanovinyl (DCV)-substituted oligothiophenes consist of both electron donor and acceptor ligands, which makes them promising materials for organic electronics. Here, we studied the structural and electronic properties of methyl-substituted dicyanovinyl-quinquethiophenes (DCV5T-Me₂) adsorbed on different metal surfaces, namely Au(111), Ag(111), and Cu(111), by using low-temperature scanning tunneling microscopy/spectroscopy (STM/STS). It is found that the assembled structures of DCV5T-Me₂ and the corresponding electronic properties vary depending on the underlying substrates. On Au(111) and Ag(111), compact organic islands are formed through intermolecular hydrogen bonding and electrostatic interactions. The lowest unoccupied molecular orbital (LUMO) and LUMO+1 of DCV5T-Me₂ are lower in energy on Ag(111) than those on Au(111), due to the stronger molecule-surface interaction when adsorbed on Ag(111). Moreover, orbital distributions of the LUMO and LUMO+1 in dI/dV maps on Au(111) and Ag(111) are the same as the DFT-calculated orbital distributions in gas phase, which indicates physisorption. In contrast, chemisorption dominates on Cu(111), where no ordered assemblies of DCV5T-Me₂ could be formed and resonances from the LUMO and LUMO+1 vanish. The present study highlights the key role of molecule-substrate interactions in determining the properties of organic nanostructures and provides valuable insights for designing next-generation organic electronics.