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

Abstract

The adsorption structures of three thiophene derivatives and one pyrrole derivative on Au(111) 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=0.55V. 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(111) 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.