“Naked” Iron-5,10,15-triphenylcorrole on Cu(111): Observation of Chirality on a Surface and Manipulation of Multiple Conformational States by STM Stefan Kuck, † Germar Hoffmann,* ,† Martin Bro ¨ ring, ‡ Martin Fechtel, ‡ Markus Funk, ‡ and Roland Wiesendanger † Institute of Applied Physics, UniVersity of Hamburg, Germany, and Fachbereich Chemie, Philipps-UniVersita ¨t Marburg, Germany Received August 5, 2008; E-mail: ghoffman@physnet.uni-hamburg.de The observation and manipulation of nanoobjects on metallic surfaces by scanning tunneling microscopy (STM) have reached an amazing level of sophistication. 1 Among the different classes of molecules studied as individuals on surfaces, metalloporphyrins and phthalocyanines have proven the most successful due to their nanoscale size and peripheral as well as electronic variability. 2 Properties like mobility, magnetism, conformation, and intramo- lecular interaction can be imprinted on the molecular level by synthetic means and then used directly in nanoscience. In particular, molecular sensors and actuators, conformational switches, self- assembled nanostructures, and artificial aggregates have successfully been built by design from metalloporphyrins and could be investigated and modeled down to atomic resolution. 3 In addition, the high stability and easy accessibility of metalloporphyrins and phthalocyanines have contributed significantly to the success of this class of functional molecules. A new member of the metalloporphyrinoid class, the one-carbon short corrole, has been developed in the past decade to be a very accessible, easily tunable compound with many potential applica- tions in material science and catalysis. 4 Corroles differ from the parent porphyrin mainly by their lower inherent symmetry and the smaller cavity. In addition, the fully deprotonated macrocycle is formally trisanionic as opposed to only dianionic porphyrin ligands. The latter feature leads to more intense metal-ligand interactions in metal chelates and to interesting electronic structures. In a pilot study we have now established the suitability of the simple iron complexes of 5,10,15-triphenylcorrole (FeTPC) 5 for vapor deposi- tion under ultrahigh vacuum conditions and were able to study individual iron triarylcorrole molecules on a Cu(111) surface by low-temperature STM. Other than for the structurally related Fe II porphyrins, 6 all attempts to prepare and study “naked” FeTPC molecules, i.e., without attached axial ligands, in bulk have failed. Here, we demonstrate the stabilization of FeTPC as adsorbates on a surface. Figure 1 shows STM images of isolated FeTPC molecules adsorbed on Cu(111) as sublimed from different starting materials. The appearances of the molecules vary slightly with the (unknown) tip shape, but indications for variations of molecular structures were not observed. Instead, when molecules from different starting materials were prepared in parallel on the same surface, molecules were indistinguishable. We interpret these molecules as intact “naked” FeTPC molecules. Therefore, in the following we will simply denote molecules as FeTPC molecules independent of the originating source. Figure 2a presents a high-resolution image of an isolated FeTPC molecule on a Cu(111) surface. FeTPC appears without any symmetry. Each molecule has three dominant outer and elongated protrusions at its opposite ends which represent the phenyl legs and one unoccupied end which breaks mirror symmetry. For the corrole center, we find an accentuated backbone in a cigar shape with one side highlighted (see also blue/green sketch in Figure 3). This side is located between two outer protrusions. The interpreta- tion of the adsorption geometry follows in a natural way the observed symmetry. The corrole macrocycle is deformed into a saddle conformation, and all three phenyl legs are twisted relative to the surface normal. The accentuated backbone reflects the upward bend pyrrolic units of the corrole macrocycle, whereas the other pyrrolic units show toward the surface plane. Additionally, the macrocycle is slightly tilted relative to the plane of the substrate due to the asymmetry of the phenyl legs with one side lifted by the supporting phenyl legs. This interpretation is demonstrated by the overlaid structure of FeTPC and is in line with the interpretation † University of Hamburg. ‡ Philipps-Universita ¨t Marburg. Figure 1. Iron(III) triphenylcorroles with different axial ligands employed in this study along with their appearances in STM images (all, 3 × 3 nm 2 , -1000 mV, 100 pA). Figure 2. (a) High resolution topographic image of an individual FeTPC molecule adsorbed on a Cu(111) surface. The overlaid model is scaled to the image size and illustrates the proposed saddle conformation of the corrole macrocycle with twisted phenyl legs (2 × 2 nm 2 , -1000 mV, 100 pA). (b) FeTPC and FeTPP molecules on Cu(111) (6 × 6 nm 2 , -1000 mV, 300 pA). (c) After manipulation with the STM tip, the FeTPC molecule in (b) turned by 60° clockwise. (d) Another manipulation step led to a turn of only 30° and exchange of upward and downward bend axes, a change of chirality. (e and f) Manipulation of an FeTPC molecule into a mirror symmetric conformation (3 × 3 nm 2 , -1000 mV, 300 pA). Published on Web 10/04/2008 10.1021/ja8059478 CCC: $40.75  2008 American Chemical Society 14072 9 J. AM. CHEM. SOC. 2008, 130, 14072–14073