H-Bonding Tuned Self-Assembly of Phenylene-Thiophene-Thiophene-Phenylene Derivatives at Surfaces: Structural and Electrical Studies

Several physicochemical properties of molecular ensembles can be modulated by controlling intermolecular interactions. The design and synthesis of pi-conjugated rodlike molecules exposing groups that can undergo H-bondings was exploited to develop materials featuring tunable 2D self-assembly at surfaces, thermal stability, order in micrometer-thick films, and electrical characteristics in organic field-effect transistors (OFETs). As a model system, we have chosen phenylene thiophene thiophene phenylene derivatives with side groups exposing either COOH or COOMe moieties. The structure and dynamics within monolayers at the solid-liquid interface was explored by in-situ scanning tunneling microscopy (STM) experiments. The thermal behavior of the materials was investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The order in micrometer-thick films was studied by grazing-incidence small-angle X-ray scattering (GISAXS), whereas the electrical characteristics of the different systems were studied when self-assembled in thin films in a bottom-gate and bottom-contact field-effect transistor.