The adsorption of hexahexylduodecithiophene (12T) on a Au(111) electrode was investigated by using cyclic voltammetry (CV) and in situ electrochemical, scanning tunneling microscopy (EC-STM.) in 0.10 M HCIO 4. Potential control at 0.20 V (vs RHE) revealed adlayer structures of mostly folded and rarely angular (oblique) and extended conformations on a reconstructed Au(111)-(√3×22) surface. The angular and extended conformations predominate when the electrode potential is increased to 0.35 and 0.60 V. Folded structures are still evident, but dynamic STM, studies showed, unfolding of this conformation. With molecular STM. imaging of 12T adlayers, we address the packing arrangement and conformational changes of 12T admolecules on the reconstructed Au(111) electrode surface.