Adlayer structures of thiophene and pyrrole derivatives on Au(1 1 1) probed by scanning tunneling microscopy

• The adlayers of four thiophene/pyrrole derivatives on Au(1 1 1) were investigated.
• HT and DT molecules form similar adsorption structure with S–S interaction stabilized dimer building block.
• The BDD compounds show the tetramer based monolayer structure.
• Every four ODP molecules form a tetramer with interdigitated alkyl chains in the adlayer.

The adsorption structures of three thiophene derivatives and one pyrrole derivative on Au(1 1 1) have been investigated by scanning tunneling microscopy (STM) and cyclic voltammetry in 0.1 M HClO4. The structural details and differences of four monolayers are examined by STM. All the four monomers arrange into ordered adlayers at E = 0.55 V. Two kinds of alkyl substituted thiophenes, 3-hexylthiophene (HT) and 3-decylthiophene (DT), show similar adsorption behavior. Molecules form dimer basic units through S–S bonding and arrange into the “U-shaped like” patterns. 2-((6-Bromohexyloxy)methyl)-2,3-dihydrothieno[3,4-b][1,4]dioxine (BDD) molecules with an 3,4-ethylenedioxythiophene (EDOT) as molecular skeleton assemble into liner structure with tetramers as building unit. 1-Octadecylpyrrole (ODP) with alkylated pyrrole ring form a lamella structure on Au(1 1 1) with interdigitated alkyl chains. The flat-lying configuration for the four monomers is beneficial to enhance the molecule–substrate interaction, which plays an important role to stabilize the organic thin film.

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