Unveiling the Interplay between a Au(100) Electrode, Adsorbed TTMAPP Porphyrin Cations, and Iodide Anions: An EC-STM and CV Study

The self-assembly of TTMAPP porphyrin molecules on a Au(100) electrode has been studied through combined cyclic voltammetry (CV) and in situ scanning tunneling microscopy (STM) investigations. In total, up to 11 different long-range ordered phases of TTMAPP molecules were found to exist, with the electrode potential acting as the only driving force for the observed phase transitions between the structures. The results also show that TTMAPP molecules, on the one hand, adsorbed on the I-free (1 x 1) Au(100) surface hinder the readsorption of iodine, while on the other hand, adsorbed on the I-modified Au(100) surface, hinder the desorption of iodine from the surface, respectively. The study revealed that the readsorption of iodine on the TTMAPP-covered Au(100) surface can be controlled by the scan rate of the electrode potential. This work highlights the potential-induced modification of the noncovalent interactions, namely, van der Waals and electrostatic forces, between the TTMAPP molecules and the substrate, which play a crucial role in determining the structural self-assembly of the TTMAPP molecules on the surface.