Self-assembled nanostructures of a series of linear oligothiophene derivatives adsorbed on surfaces

Abstract

Many previous studies have shown that the molecular structures of oligothiophene derivatives including molecular skeleton and alkyl chains have a significant effect on their self-assemblies on the surface. In this work, a series of linear oligothiophene derivatives (DCV-nT-Hex, n = 3∼11) modified with terminal dicyanovinyls and alkyl chains were adopted to further investigate the different assembly behaviors at liquid-solid interface by scanning tunneling microscopy (STM). Interestingly, via the hydrogen bonding and van der Waals interactions, DCV-3T-Hex formed zigzag and flower structures while DCV-nT-Hex (n = 4∼11) formed lamellar structures. Density functional theory (DFT) calculations show that for the most energetically favorable configurations of DCV-nT-Hex, the different distribution of alkyl chains affected intermolecular interactions, and ultimately led to the different assembled structures. The zigzag and flower structures of DCV-3T-Hex had preferential thermodynamic stability compared to other structures of DCV-nT-Hex (n = 4∼11). In addition, self-assembled nanostructures of DCV-nT-Hex molecules with even numbers (n = 4, 6, 8, 10) were overall more stable than those with odd numbers (n = 5, 7, 9, 11), and the stability of the self-assembled structure was weakened with the extension of the molecular backbone, individually. The orientation of molecular alkyl chains was found to greatly affect the intermolecular interactions and thus leading to various self-assembly structures of DCV-nT-Hex (n = 3∼11). The self-assembly behaviors of linear oligothiophene derivatives DCV-nT-Hex (n = 3∼11) driven by hydrogen bond and van der Waals force were investigated by STM and DFT calculations, and the orientation of molecular alkyl chains was found to greatly affect the intermolecular interactions.