Abstract
The modelling of long-range ordered nanostructures is still a major issue for the scientific community. In this work, the self-assembly of redox-active tetra(N-methyl-4-pyridyl)-porphyrin cations (H2TMPyP) on an iodine-modified Au(100) electrode surface has been studied by means of Cyclic Voltammetry (CV) and in-situ Electrochemical Scanning Tunneling Microscopy (EC-STM) with submolecular resolution. While the CV measurements enable conclusions about the charge state of the organic species, in particular, the potentio-dynamic in situ STM results provide new insights into the self-assembly phenomena at the solid-liquid interface. In this work, we concentrate on the regime of positive electrode potentials in which the adsorbed molecules are not reduced yet. In this potential regime, the spontaneous adsorption of the H2TMPyP molecules on the anion precovered surface yields the formation of up to five different potential-dependent long-range ordered porphyrin phases. Potentio-dynamic STM measurements, as a function of the applied electrode potential, show that the existing ordered phases are the result of a combination of van der Waals and electrostatic interactions.
Highlights
One of the major challenges in the development of supramolecular nanoarchitectures is to find effective and flexible methods in order to create nanostructures with long range order [1,2]
Supramolecular self-assembly attracted much attention by the scientific community: as a well-known bottom-up method, molecular self-assembly on surfaces is a simple and fast tool to build nanoscale structures, which can be readily tuned by the on-purpose synthesis of appropriate molecular building blocks, and, thereby, the design of the noncovalent interactions between the molecules and the substrate and the molecules themselves [3,4,5,6,7]
The first surface reduction/re-oxidation step of the molecules is indicated by the peak couple Pred /Pox, as verified by the following Electrochemical Scanning Tunneling Microscopy (EC-Scanning Tunneling Microscopy (STM)) measurements
Summary
One of the major challenges in the development of supramolecular nanoarchitectures is to find effective and flexible methods in order to create nanostructures with long range order [1,2]. To direct the ordering process of the supramolecular nanoarchitectures, one can take advantage of well-defined single crystal surfaces, which can serve as electronic and/or geometric templates due to the operation of specific adsorbate-substrate interactions. Porphyrins, due to the wide range of potential applications of this class prototypical systems for the fabrication and design of supramolecular nanoarchitectures and the of molecules, e.g., in cancer therapy [16,17], catalysis [18,19], and sensing [20,21], have become characterization of their formation mechanism [22,23]. Waals iodine type [26,27,28]
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