Oligothiophenes substituted with the thionitrile group: synthesis, characterization, and thin-film formation on gold substrates

Thiol mimics are molecules that are less chemically reactive than thiols but that also attach to a metal surface through a metal-thiolate bond; thus, they give an alternative method of attaching organic semiconductors to a surface. The synthesis and molecular characterization of substituted bithiophenes and terthiophenes containing at least one thionitrile substituent (a "protected thiol") are presented. Photoluminescence spectroscopy shows that the nitrile groups are not in conjugation with the oligothiophene core. Single-crystal X-ray structures of two bithiophenes (T2SCN2 and BrT2SCN, where T = 2,5-thienylene) show that the thionitriles have extended intermolecular contacts and pi-stacking in the solid state. All the synthesized compounds form thin films on gold substrates, as shown by electrochemical capacitance measurements. Atomic force microscopy demonstrates uniform coverage and shows good crystallite overlap in the films, with crystallite size dependent on the number of intermolecular contacts in the solid-state structure.