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Tuning the Electronic and Dynamical Properties of a Molecule by Atom Trapping Chemistry Van Dong Pham, Vincent Repain, Cyril Chacon, Amandine Bellec, Yann Girard, Sylvie Rousset, Enrique Abad, Yannick J. Dappe, Alexander Smogunov, and Jérôme Lagoute ACS Nano, Just Accepted Manuscript • DOI: 10.1021/acsnano.7b05235 • Publication Date (Web): 29 Sep 2017 Downloaded from http://pubs.acs.org on September 30, 2017

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Tuning the Electronic and Dynamical Properties of a Molecule by Atom Trapping Chemistry Van Dong Pham,†,§ Vincent Repain,† Cyril Chacon,† Amandine Bellec,† Yann Girard,† Sylvie Rousset,† Enrique Abad,‡ Yannick J. Dappe,¶ Alexander Smogunov,¶ and Jérôme Lagoute∗,† †Laboratoire Matériaux et Phénomènes Quantiques, UMR7162, Université Paris Diderot Paris 7, Sorbonne Paris Cité, CNRS, UMR 7162 case courrier 7021, 75205 Paris 13, France ‡Departamento F´ısica Teórica de la Materia Condensada, Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, E-28049, Madrid, Spain ¶SPEC, CEA, CNRS, Université Paris-Saclay, CEA Saclay, 91191 Gif-sur-Yvette Cedex, France §Current address: Department of Physics, Friedrich-Alexander University of Erlangen-N¨ urnberg, Erwin-Rommel-Strasse 1, 91058 Erlangen, Germany E-mail: [email protected]

Abstract The ability to trap adatoms with an organic molecule on a surface has been used to obtain a range of molecular functionalities controlled by the choice of the molecular trapping site and local deprotonation. The tetraphenylporphyrin molecule used in this study contains three types of trapping site: two carbon rings (phenyl and pyrrole) and the center of a macrocycle. Catching a gold adatom on the carbon rings leads to an electronic doping of the molecule 1 ACS Paragon Plus Environment

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while trapping the adatom at the macrocycle center with single deprotonation leads to a molecular rotor and a second deprotonation leads to a molecular jumper. We call ’atom trapping chemistry’ the control of the structure, electronic and dynamical properties of a molecule achieved by trapping metallic atoms with a molecule on a surface. In addition to the examples previously described, we show that more complex structures can be envisaged.

Keywords scanning tunneling microscopy, single-molecule manipulation, molecular rotor, density functional theory Nanotechnology aims at controlling the matter at the atomic level in order to build nanometer scale functional components. It is conceivable to build-up atomically controlled nano-objects with desired functions and performances by manipulating individual atoms and molecules with a scanning tunneling microscope (STM). Using this technique, it has been shown that organic molecules can be used to trap single adatoms on a surface allowing to control the electronic spectrum of a molecule by doping 1 or bond formation, 2 to trap and drive atoms 3,4 or to confine a molecular motion to rotation during manipulation. 5 A particular attention has been given to the manipulation of macrocyclic molecules such as porphyrin 6 or phtalocyanine. It has been shown that an electronic doping of individual molecules with individual atoms at different binding sites can be achieved. 7 Metallation can also be obtained by exchanging the center hydrogens to a metal atom. 8–12 Dehydrogenation was also studied by STM, 13–15 and lastly, it was shown that molecules can be pinned on a surface by neighboring adatoms. 16 Here we go one step further, we show that all the functionalities previously mentioned can be achieved in a single system. This is achieved by manipulating a single molecule with a single metallic atom, the functionality is tuned only by changing the location of the metallic atom in combination with controlled dehydrogenation. This demonstrates the large potential

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of tunability of a single molecule by ’atom trapping chemistry’ which refers to the ability to change the molecular functionality by attaching an adatom to a specific site (depending on the desired function) of a molecule and eventually inducing a chemical bond promoted by tipinduced deprotonation. We illustrate this by combining a gold adatom on a Au(111) surface with a tetraphenylporphyrin molecule (H2 TPP) that contains three types of trapping sites: phenyl groups, pyrrole groups, and the center of the macrocycle pointed by four nitrogen atoms (two of them being hydrogenated). The structures and properties that can be obtained are illustrated in Fig. 1 with the principle of the manipulation process. As will be shown, atom trapping on a phenyl or pyrrole group leads to an electronic doping of the molecule, atom trapping at the center of the macrocycle combined with single deprotonation leads to a molecular rotor (rotation under voltage pulse excitation), while a second deprotonation leads to a molecular jumper (translation and rotation under voltage pulse excitation).

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Figure 1: Atom trapping chemistry of a H2 TPP porphyrin molecule with an Au adatom. (a) Illustration of the different porphyrin-adatom molecules and properties obtained by trapping an Au adatom (orange dot) below a H2 TPP molecule on a Au(111) surface. (b) 3D view of the Au(111) surface covered by H2 TPP single molecules and Au single adatoms, and schematic representation of the manipulation of a molecule to an adatom allowing to trap the adatom below the molecule.


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Results and Discussion In order to obtain single molecules and adatoms on the surface we have deposited H2 TPP followed by the extraction of Au adatoms from the Au(111) substrate (see Supplementary Section 1). As shown in Fig. 2a, an individual H2 TPP molecule appears with four lobes corresponding to the phenyl groups and an inner ring corresponding to the macrocycle. 17 Individual Au adatoms appear as single dots with a typical height of 1.3 ˚ A at a tunneling condition of U =+1 V, I=100 pA. dI/dV spectra measured above these adatoms show a broad resonance peak at +3.1 V (see Supplementary Section 1), which is typical of monatomic single adatom on a surface exhibiting a Shockley state (as it was shown on Cu adatoms on Cu(111) 18 ). Using lateral manipulation (see methods), we moved a H2 TPP molecule toward an adatom that we attached either to a phenyl group (this species will be noted Auϕ -H2 TPP) or to a pyrrole group (noted Auπ -H2 TPP) as shown in Fig. 2a,b. In both cases, the height of the group connected increases, which allows to identify where the adatom is located. The molecule-adatom contact shifts the HOMO and LUMO states to lower energy respectively by 0.08±0.01 eV and 0.10±0.02 eV for Auϕ -H2 TPP and by 0.10±0.02 eV and 0.14±0.03 eV for Auπ -H2 TPP (see Fig. 2c). We have verified that this is due to the contact with the adatom and not to a possible conformational change of the molecule during the manipulation (see Supplementary Section 2). These shifts indicate a charge transfer, leading to an n-doping of the molecule. The shapes of the HOMO and LUMO states are revealed by the dI/dV maps that are shown with the topographic images in Fig. 2d,e. The HOMO state allows to identify the conformation of the molecule. The molecule-surface interaction induces a rotation of the pyrrole and phenyl groups, in particular two opposite pyrrole groups are pointing upward (i.e., carbon atoms higher than nitrogen with respect to the surface), while the two others are pointing downward. 17 Despite the decrease of local density of states observed at the location of the trapped adatom, a line can be seen in the center of the HOMO state that is 4 ACS Paragon Plus Environment

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aligned with the pyrrole groups pointing upward. 17 This allows to identify the pyrrole groups pointing upward and downward, and reveals that in all Auπ -H2 TPP that we have built, the Au adatom is attached to the pyrrole groups pointing upward. Indeed, inserting an adatom below a pyrrole pointing downward may involve a rotation of the pyrrole or a lifting of the molecule which is not favorable for adatom insertion. Note that the two tautomer forms of the molecules can also be observed and controlled experimentally (see Supplementary Section 3).

In order to interpret the experimental observations, we have modeled the Auϕ -H2 TPP and Auπ -H2 TPP systems theoretically using Density Functional Theory (DFT) (see Methods). We have optimized the structures and calculated the corresponding Density of States (DOS), as shown in Fig. 2f. The result is in good agreement with the experiment as we can observe a shift of the curve toward negative energy. This shift can be interpreted as a weak doping of the molecular system due to the specific interaction with the gold adatom, leading to a small charge transfer from the surface to the molecule. In agreement with the experimental data, the shift is larger on Auπ -H2 TPP than on Auϕ -H2 TPP, which might be attributed to the closer proximity of the pyrrole group to the nitrogen core of the molecule, yielding a more effective charge transfer. Indeed, as determined by the calculations, the nitrogen-gold adatom distance is shorter in the case of pyrrole than in the case of phenyl (see Table 1 in Supplementary Section 4), which implies a bigger overlap between electronic densities. This is characteristic of a stronger interaction with the gold adatom in the pyrrole case, which leads to the stronger charge transfer. This behaviour is also corroborated in the case of pyrrole by a larger binding energy of the H2 TPP molecule to the system adatom + surface and a lower binding energy of the system H2 TPP molecule + adatom to the surface (see Table 2 in Supplementary Section 4). This picture is further supported by the results reported by Mielke et al. 19 on a third configuration where the Au adatom is located inside the macrocycle, close to the center, without deprotonation. The authors measured a rigid downshift of the HOMO and LUMO states of


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Figure 2: Doping of a porphyrin molecule with an Au adatom. (a) (left) Image of a H2 TPP molecule and an Au adatom. (Right) Image measured after moving the molecule toward the adatom by lateral manipulation to form a Auϕ -H2 TPP species (5×5 nm2 , U =1 V, I=100 pA). (b) Same measurements as in (a) for a Auπ -H2 TPP molecule. The structures above (a) and (b) are top views of the DFT calculated optimized structures for both species adsorbed on Au(111). (c) dI/dV spectra recorded above a pyrrole group on a molecule before (black curve) and after (red curve) attaching an Au adatom to a phenyl group. The blue curve shows the dI/dV spectrum of a molecule after attaching an Au adatom to a pyrrole group. The dashed vertical line indicates the energy of the HOMO and LUMO states of H2 TPP for better visualization of the energy shift after attaching an adatom. The insets show the distribution of HOMO and LUMO energies measured on H2 TPP before manipulation (black), on Auϕ -H2 TPP (red) and on Auπ -H2 TPP (blue). (d) Topographic images (left) and dI/dV maps (right) measured close to the LUMO energy at +1.5 V (top) and close to the HOMO energy at -0.8 V (bottom) of a Auϕ -H2 TPP molecule (3.5×3.5 nm2 ). (e) Topographic images (left) and dI/dV maps (right) measured close to the LUMO energy at +1.4 V (top) and close to the HOMO energy at -0.8 V (bottom) of a Auπ -H2 TPP molecule (3.5×3.5 nm2 ). (f) Calculated DOS of H2 TPP (black), Auϕ -H2 TPP (red) and Auπ -H2 TPP on Au(111).


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about 0.5 eV. This larger value is in line with the previous discussion.

The Au-porphyrin molecules discussed above can be moved by lateral manipulation as a single unit on the surface meaning that the adatom has been trapped by the molecule to form a stable entity. However cumulative lateral manipulations can lead to the formation of another state, probably due to transitory conformations coupled with the molecule-tip/surface interactions during the manipulation process. This molecular state is described hereafter. In Fig. 3, we show another structure obtained after a series of lateral manipulations of a Auϕ -H2 TPP (we obtained that species four times starting from Auϕ -H2 TPP and two times starting from Auπ -H2 TPP). In contrast with the previous cases, the electronic structure of that species reveals a large shift of the molecular orbitals to higher energy. As shown in the dI/dV spectra of Fig. 3a (red curve), HOMO-1, HOMO and LUMO states appear at -1.1 V, -0.4 V and 1.7 V, respectively. The corresponding topographic images and dI/dV maps are displayed in Fig. 3b. The HOMO state reveals a central protrusion that is slightly off-centered, indicating that the adatom is located inside the macrocycle and slightly shifted toward a pyrrole group pointing downward.

In sharp contrast with previous cases, this molecule exhibits a dynamical response to a voltage pulse, applied above any part of the molecule, that induces a rotation. Such a dynamical behaviour has been used for the manipulation of molecules on surfaces 20–24 and attributed to an inelastic tunneling excitation. In Fig. 3c we show the STM images revealing the three possible orientations that can be reached by this molecule when applying a voltage pulse at +2 V during 6 s. These orientations correspond to an alignment of the axis between the upward pyrrole groups (dashed lines in Fig. 3c) with the close-packed atomic row directions of Au(111). We show in the Supplementary Movie 1 a more extensive series of such images where a pulse of +2 V was applied during 6 s at the same position between each image above the center of the


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Figure 3: Molecular rotor. (a), dI/dV spectrum of a bare H2 TPP molecule before manipulation (black curve) and the same molecule functionalized with an Au adatom at the center forming a molecular rotor (red curve). The HOMO and LUMO states shift to higher energy after functionalization. The topography of the molecular rotor is shown in the inset (10×10 nm2 , U =+1 V, I=100 pA). (b) Topography (top) and dI/dV maps (bottom) of the molecular rotor at bias voltages corresponding to the HOMO-1 (-1.1 V), HOMO (-0.4 V), and LUMO (+1.7 V) states (3.5×3.5 nm2 ). (c) Images of the three orientations that the molecular rotor can reach after excitation by a voltage pulse of +2 V (7×7 nm2 , U =+1 V, I=100 pA). The inset indicates the atomic lattice orientation of the Au(111) substrate deduced from the orientation of the reconstruction lines in the topographic images. (d) Current versus time recorded when the tip is above the molecule, slightly off-centered, during a voltage pulse. (e) Side view (top) of the optimized structure of the molecular rotor on Au(111), and top view of the same structure (bottom, substrate atoms not shown). (f) Calculated DOS of a H2 TPP (black) and of a rotor (red) on Au(111).


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molecule. We have also performed measurements with a control molecule of H2 TPP where the same pulse (+2.1 V during 1 s) was applied above the center of the rotor and the control molecule between each image. The resulting movie (see Supplementary Movie 2) shows that only the rotor is rotating and the H2 TPP does not move. However one can clearly see the reversible random switching of the reference molecule between its two tautomer forms. The tunneling current recorded during the voltage pulse of 120 s reveals a three level telegraph signal corresponding to three orientations of the molecule (Fig. 3d). Sharp spikes in the current can also be seen in the signal that we attribute to the rotation or to an intermediate positions with a short lifetime. Our series of data also reveal that the rotation direction is random. The molecular rotor described here was located on a fcc area of the reconstruction of the Au(111) surface. In order to investigate the effect of the adsorption site, we also created a molecular rotor close to an elbow site of the herringbone reconstruction. In that case, seven different orientations were measured, which we attribute to a change of local symmetry at the elbow of the reconstruction (see Supplementary Section 5). The rotational motion is only triggered above a certain threshold energy. When we used a series of different voltage pulses (with a duration of 50 s) from +0.5 V to +2.1 V, with a voltage step of 0.1 V, the molecule only started to rotate at a threshold energy of +1.7 eV. At negative bias, down to -2V, the molecules did not undergo any rotation. Although further investigation is needed to fully understand the physical process leading to the rotation, our data suggest that the rotation is due to a vibronic transition similar to previous reports. 20,23 In order to understand the structure and properties of rotor species, we have performed DFT calculations. We have optimized the configuration after removing one hydrogen atom in the molecule (see Fig. 3e). The reasons for the hydrogen removal is twofold : firstly, the dI/dV curve shown in Fig. 3a exhibits an important shift to positive energies, which can be interpreted as an important loss of charges from molecule. Secondly, the DFT optimization is performed at 0 K, meaning that the potential barrier to be overcome for removing a hydrogen


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atom is too high to observe this removal process in the present calculation. The calculated binding energy of a hydrogen atom in the center of the molecule is -5.8 eV for H2 TPP and reduces to -4.77 eV for the rotor configuration. Note also that calculations performed on the molecule where we keep the two inner hydrogen atoms do not reproduce the experimental observations. The calculated DOS, of the configuration with one hydrogen, is presented in Fig. 3f, and as expected, we can observe a strong shift toward positive energies, which confirms the removal of the hydrogen atom. The HOMO peak is now located at -0.55 eV, which is in good agreement with the experimental measurements at -0.4 V. Also, since the gold adatom remains strongly attached to the gold surface (see Supplementary Section 4), as in the phenyl and pyrrole cases, it is easily understandable that the gold doping is comparable to those two previous cases and cannot compensate the loss of one electron due to the hydrogen removal. The present case is then summarized as a molecular p-doping due to hydrogen removal that overcomes the slight n-doping due to the interaction with gold. The system can be further tuned by increasing the atom-molecule interaction and decreasing the atom-surface interaction. Two manipulation paths allow to reach the same state that is described in Fig. 4: a cumulative lateral manipulation of a rotor, or a series of voltage pulses at +2 V (see in Fig. 4c the transition measured in the tunnel current signal when a pulse of 180 s is applied). The topography image is close to the initial H2 TPP molecule, however the apparent height is larger (1.97±0.02 ˚ A) than that of a bare H2 TPP (1.55±0.02 ˚ A). A larger difference is observed in the dI/dV spectroscopy. The HOMO and LUMO resonances are now located at -1.7 V and +1 V, respectively, and are therefore both shifted to lower energy as compared to H2 TPP. To understand more in detail the electronic properties of this molecule, we performed dI/dV maps that are shown in Fig. 4b. The symmetry of these maps and of the topographic images suggests that the Au adatom is now exactly at the center of the molecule. The structure of this molecule will be determined below with the support of theoretical calculations. Concerning the dynamic behaviour, this molecule acts as a molecular jumper, a voltage pulse


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Figure 4: Molecular jumper. (a) dI/dV spectrum of a bare H2 TPP molecule before manipulation (black curve) and the same molecule functionalized with an Au adatom below the center forming a molecular jumper (red curve) (inset: topographic image, 4×4 nm2 , U =+1 V, I=100 pA). (b) Topographic images (top) and dI/dV maps (bottom) of a molecular jumper recorded at its HOMO (-1 V) and LUMO (+1.7 V) energies (3.5×3.5 nm2 ). (c) Tunneling current recorded when the tip is placed above a rotor molecule during a voltage pulse, showing the transition between a molecular rotor and a molecular jumper. (d) Topographic image (4×4 nm2 , U =+1 V, I=100 pA) of a jumper molecule with marks indicating the position and orientation of the molecule after applying bias pulses at +1.5 V during 6 s always at the same position indicated by the white cross. (e) Topographic images before and after applying a voltage pulse at +2 V during 3 s with the tip located 1.5 nm away from the molecule center as indicated by the white cross (10×10 nm2 , U =-0.8 V, I=100 pA). (f) Side view (left) of the calculated relaxed structure of the molecular jumper on Au(111). Top view (right) of the molecule (atoms of the substrate not shown). (g) Calculated DOS of H2 TPP (black) and of the molecular jumper (red) on Au(111). (h) Calculated energy of a molecular jumper (red) and a rotor (black) as a function of lateral displacement. The energy barrier for diffusion is much higher for the rotor (15 eV) than for the molecular jumper (1.7 eV).


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of typically 6 s now induces both rotation and translation, with a translational distance that can be more than 10 ˚ A (Fig. 4d) and a position of the molecule that stays in an area centered around the tip position. A larger sequence of images is shown in the Supplementary Movie 3 (where a pulse of +1.5 V was applied during 6 s between each image) that clearly marks the difference with the behaviour of the rotor. This difference is further confirmed by the time trace of the tunneling current recorded during the voltage pulse (with a duration of 180 s) that is very complex, exhibiting many levels (Fig. 4c). We have studied the ability of moving the molecule as a function of the lateral tip-molecule distance, and found that a motion can be induced even if the tip is beside the molecule and not on top of it, at a distance of 1.5 nm from the molecule center (Fig. 4e). This suggests that the motion is induced by the electric field applied with the STM tip. Note that this is different from the case of the rotor, where we only could induce a rotation when the tip was above the molecule and not beside it. In addition we observed that the motion of the molecule could only be induced with positive bias pulse and not with negative bias pulse. This indicates that the direction of the electric field plays a role in the excitation of the molecular motion. The strong shift of molecular levels observed in Fig. 4a could be reproduced in our calculation only by establishing a strong connection between the gold adatom and the molecule, by decoupling the adatom from the surface, and removing the second hydrogen atom. We have consequently simulated this configuration (displayed in Fig. 4f) and the result of the DOS calculation is presented in Fig. 4g. As expected, the HOMO and LUMO states are now shifted to lower energy as they appear at -1.75 eV +0.7 eV respectively, in good agreement with the experimental observations. Overall, the explanation of the peaks positions is indeed related to the interaction between the gold adatom and the molecule, since the molecular jumper can now be seen as a full gold porphyrin. This is also confirmed by the calculated distances and binding energies (see Table 1 and 2 in Supplementary Section 4) where the gold adatom is found to be strongly bonded to the porphyrin and decoupled from the surface. In that respect, the gold adatom is not connected anymore to the gold surface, which


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is reflected in the ability of ”easy motion” of the molecule on the surface with respect to the molecular rotor. This aspect has been probed theoretically by calculating the successive ¯ direction of the surface, energies of a molecular rotor and jumper displaced along the [21¯1] without optimization. This gives an approximation of the potential barrier that has to be overcome by the molecule to slide on the surface. The result of this calculation is presented in Fig. 4h, as the energy variation versus the molecular displacement on the surface. One can immediately notice the important potential barrier for the molecular rotor at around 15 eV, when the energy variation is rather constant at around 1.7 eV for the molecular jumper.

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Figure 5: Off-centered rotor obtained by trapping a second adatom with a molecular jumper. (a)-(d), Rotation around a second adatom attached to a phenyl group of a molecular jumper. The rotation is induced by a voltage pulse at +2 V during 6 s applied above the second adatom that constitute the rotation axis of this molecular rotor. The number of pulses needed to induce a rotation after images a, b and c was 2, 10 and 3, respectively. (10×10 nm2 , U =+1 V, I=100 pA). The H2 TPP molecule on the right does not rotate when the same voltage is applied. (e) dI/dV spectrum of the molecular jumper before connection to the second adatom (black curve) and after connection (red curve). The vertical dashed lines are guide to the eye of the position of the peaks for the two species. The concept of atom trapping chemistry brings opportunities to achieve eventually more functionalities by designing complex structures on demand. Incorporating two atoms in a molecule can be used to attain a structure that combines the functionality of two activated trapping sites. Coupling a series of molecular rotor may allow to achieve a molecular gearing and make a primitive molecular motor. To illustrate the case of functionalisation by two adatoms, we fabricated a molecular rotor with off-centered rotational axis by combining a


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molecular jumper with a second adatom trapped at a phenyl group. We manipulated a jumper molecule toward a second Au adatom until it is attached to the phenyl group. Using a bias voltage pulse at +2 V during 6 s, the molecule rotates around the adatom as can be seen in Fig. 5a-d. In that structure, the atom trapped in the center allows to activate the rotation and translation under excitation with the STM tip. The second atom allows to fix the position of one phenyl group, leading to the overall property of off-centered rotor. Our study of the Auϕ -H2 TPP species suggest that the contact of the Au adatom to the phenyl group should induce a n-doping of the molecule. Our measurements confirm that this expected properties is observed on this species. This is revealed by the comparison of the dI/dV spectra measured on a jumper molecule before and after connecting the second adatom to a phenyl group (see Fig. 5e). We observe a slight shift of the HOMO and LUMO states to lower energies, in full agreement with the effect of Au adatom contact to a phenyl group reported for the Auϕ -H2 TPP molecule.

Conclusions In conclusion, using STM and DFT calculations we have shown that the manipulation of a single porphyrin molecule with a single gold adatom allows to reach different functionalities. Trapping the adatom below a carbon ring (phenyl or pyrrole) leads to an electron doping of the molecule. Trapping the adatom at the center of the molecule together with a single hydrogen removal leads to a molecular rotor, and a second hydrogen removal leads to a molecular jumper. More sophisticated combinations can be envisaged as we have illustrated by combining a jumper molecule with a second adatom allowing us to design a second type of rotor with off-centered axis. A full sequence starting from a single H2 TPP molecule and going through the different species is shown in the Supplementary Movie 4. These results allow to envisage bottom-up strategies in the design of functional molecules by the fabrication of


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more complex structures using atom trapping chemistry.

Methods All the experiments were performed using a STM (Scienta Omicron) operating in ultra high vacuum (UHV) at a pressure below 1×10−10 mbar and at a temperature of 5 K. The substrate consists in an initially 200 nm thick Au(111) layer grown on mica (Phasis) which was cleaned by repeatedly Ar+ sputtering (900 eV) and annealing (600 K) under UHV conditions to obtain an atomically clean surface. 5,10,15,20-Tetraphenyl-21H,23H-Porphyrin (H2 TPP) molecules (Aldrich, purity > 99.9 %) were deposited using a low temperature effusion cell (Dr. Eberl MBE-Komponenten GmbH) at 525 K on a Au(111) surface kept at 5 K . All the STM images were recorded in constant-current mode with an electrochemically etched tungsten tip. The dI/dV spectra were acquired using a lock-in detector at a frequency of ca. 670 Hz and a modulation amplitude of 35 mV. Lateral manipulation of molecules were typically achieved in constant height mode with a the tip-sample distance reduced by about 3.5 ˚ A starting from the imaging conditions. Calculations were performed using the DFT localized orbital molecular dynamics technique Fireball. 25,26 For the different molecular configurations, we have used a 8×8 slab of gold atoms in the xy plane, made of five atomic layersin z direction. The molecule has then be placed in the different specific configurations above the gold adatom (or the surface in the case without adatom) and the system has been optimized at 0 K until the atomic forces went below 0.1 eV/˚ A. Standard optimized basis set for H, C, N and Au have been used, as already considered in previous works. 27,28 Due to standard electronic level misalignment as well as underestimated value of the molecular electronic gap within the localized orbital basis set DFT method, we have used a scissor operator to correct the molecular electronic level alignment. 29–31 In that respect, we have defined the scissor potential to recover the experimentally observed molecular gap and HOMO and LUMO positions of H2 TPP on gold


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without adatom. This potential has then been used for all the configurations involving the gold adatom.

acknowledgement ANR (Agence Nationale de la Recherche) and CGI/PIA (Commissariat Général à l’Investissement /Programme d’Investissement d’Avenir) ANR-11-IDEX-0005-02 are gratefully acknowledged for their financial support of this work through the Labex SEAM (Science and Engineering for Advanced Materials and devices) ANR 11 LABX 086.

Supporting Information Available Additional data on: Production of Au adatoms on the Au(111) surface; Spectrum of H2 TPP during lateral manipulation; Tautomerisation of Au-H2 TPP; Rotor at the elbow of the herringbone reconstruction of Au(111); Movie 1: series of consecutive images of a rotor molecule where a pulse of +2 V was applied during 6 s at the center of the molecule between each image. Movie 2: Series of consecutive images where a pulse of +2.1 V was applied during 1 s above the center of a rotor and a reference H2 TPP molecule between each image. Movie 3: Series of images of a jumper molecule where a pulse of +1.5 V was applied during 6 s at the same position between each image. Movie 4: Serie of manipulations starting from a H2 TPP molecule moved by lateral manipulation toward a Au adatom to obtain a Auϕ -H2 TPP and a rotor. Voltage pulses allow to induce a rotation of the rotor and to achieve a jumper molecule that is then moved by voltage pulses until attaching to a second adatom. Further voltage pulses above the second adatom induce a rotation around that adatom. This material is available free of charge via the Internet at http://pubs.acs.org/.


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Graphical TOC Entry Doping

Au Rotor

H2TPP

Jumper

Au(111)


Tuning the Electronic and Dynamical Properties of ... - ACS Publications

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