Template-controlled on-surface synthesis of a lanthanide supernaphthalocyanine and its open-chain polycyanine counterpart

Phthalocyanines possess unique optical and electronic properties and thus are widely used in (opto)electronic devices, coatings, photodynamic therapy, etc. Extension of their π-electron systems could produce molecular materials with red-shifted absorption for a broader range of applications. However, access to expanded phthalocyanine analogues with more than four isoindoline units is challenging due to the limited synthetic possibilities. Here, we report the controlled on-surface synthesis of a gadolinium-supernaphthalocyanine macrocycle and its open-chain counterpart poly(benzodiiminoisoindoline) on a silver surface from a naphthalene dicarbonitrile precursor. Their formation is controlled by the on-surface high-dilution principle and steered by different metal templates, i.e., gadolinium atoms and the bare silver surface, which also act as oligomerization catalysts. By using scanning tunneling microscopy, photoemission spectroscopy, and density functional theory calculations, the chemical structures along with the mechanical and electronic properties of these phthalocyanine analogues with extended π-conjugation are investigated in detail.


Supplementary Discussion. 1) X-Ray Photoelectron Spectra
Supplementary Figure 1 shows the C 1s and N 1s X-ray photoelectron spectra of the different samples studied by STM. Noteworthy, the XPS data where always recorded exactly at the same samples as were used for the STM data shown in the paper and the Supplementary Discussion. This is possible because the used UHV setup contains both a scanning tunneling microscope and an XPS spectrometer connected with a fast transfer system. The deconvolution of the C 1s monolayer spectrum of the ADN monolayer shows a major and a minor component with BEs of 285.0 eV and 286.6 eV, respectively. Due to a higher electronegativity of nitrogen compared to hydrogen and carbon, the C 1s signal of the -C≡N group has a higher BE than that of the tetramethyl-tetrahydroanthracene backbone. Therefore, the major and minor components are related to the carbon atoms in tetramethyl-tetrahydroanthracene and carbonitrile (-C≡N) groups of ADN, respectively. The N 1s spectrum shows a single peak at 399.6 eV, which is a typical value for nitrogen in a -C≡N…H hydrogen bonding situation. The C 1s XP spectrum of Fe-NPc (sample in Figure 2c) shows only one peak located at 284.7 eV. Comparing to the C 1s XP spectrum of intact AND, the disappearance of the minor component (related to -C≡N) with a BE of 286.6 eV supports the transformation from the carbonitrile groups in ADN to the pyrrole and aza groups in Fe-NPc. Further evidence is provided by the related changes of the N 1s peak, which shifts towards lower BE by 1.7 eV upon formation of Fe-NPc. This result is consistent with the oxidation of iron to Fe(II) and a related gain of negative charge at the N atoms. Note that the BE (397.9 eV) of N 1s here is somewhat lower than that reported for the planar iron-phthalocyanine (398.7 eV) on Ag(111) surface. This is explained by the additional gain of electron density from the Ag(111) surface due to the stronger nitrogen-Ag(111) interaction of Fe-NPc than Fe-Pc. The underlying reason for this effect is the tilted adsorption configuration of the lobes (diiminobenzoisoindoline units) of the Fe-NPc molecule, which make the nitrogen atoms pointing down and position them closer to the Ag(111) surface. In addition, a work function change due to the deposition a slight excess of Fe atoms may play a role. The C 1s XPS signal of Gd-SNPc (sample in Figure 2e) consists of a single peak located at a BE of 285.1 eV, similar to that for Fe-NPc (284.7 eV) and thus indicating the transformation of the carbonitrile groups to the pyrrole and aza groups. The corresponding N 1s peak appears at a BE of 398.2 eV, which is close to that of Fe-NPc (397.9 eV) and indicates a 1.4 eV shift towards lower BE relative to the -C≡N related N 1s peak (399.6 eV). For the polycyanine chains, the absence of -C≡N groups is supported by the C 1s and N 1s spectra of the sample in Figure 3a. Both spectra show single peaks located at BEs of 284.8 eV and 398.1 eV, respectively, shifted toward lower BE compared to the C 1s (286.6 eV) and N 1s (399.6 eV) peaks related to the -C≡N group.

2) Structure Confirmation of Fe-NPc by Size Comparison
According to high-resolution AFM images of naphthalocyanine reported previously, 1 the distance (green line, Supplementary Figure 2a) between the centers of two oppositely positioned benzene rings in a naphthalocyanine is measured to be 16.2 ± 0.5 Å as illustrated by Supplementary Figure  2a. The distance (red line, Supplementary Figure 2a) between two adjacent benzene rings is measured to be 2.5 ± 0.5 Å. The corresponding distances of Fe-naphthalocyanine is similar as shown by the Supplementary Figure 2b. Assuming that this distance is close to the distance (red line, Supplementary Figure 2c) between the cyclohexane ring and its adjacent benzene ring, the distance between the centers of two oppositely positioned tetramethyl-cyclohexane units in Fe-NPc is then derived to be 21. . The light red ovals in panels (c) and (d) highlight the tetramethylcyclohexane moieties, which appear as bright lobes in Fe-NPc and Gd-SNPc. Black spheres represent carbon atoms; blue, nitrogen; white, hydrogen; red, iron.

3) Lateral Distance Uncertainties
The uncertainty of 0.5 Å of the measured distance in Supplementary Figure 2e is derived as show by Supplementary Figure 3 and as discussed in the following. Supplementary Figure 3 shows the apparent height profiles along the green lines overlaid on the STM images. The lobe-to-lobe distances (20.72 Å, 20.45 Å, 20.95 Å, and 20.62 Å) of four cross-shaped species, which are located at different parts of the image, have been measured. Therefore, the average value of these distances is 20.685 Å (20.7 Å), and the error bar is derived as 20.95 -20.685 Å = 0.265 Å (0.3 Å). The intrinsic uncertainty from the size of the STM image pixels accounts for another part of the final uncertainty. It is defined as the size of two pixels due to the determination of two peak maxima (2 × 100 Å/512 pixel = 0.4 Å). On this basis, the final maximum uncertainty is estimated to be 0.5 Å. This procedure for the derivation of uncertainties has also been applied to other distance measurements in the main text. Figure 3. Derivation of the uncertainties of the measured lateral distances. (a-d) Apparent height profiles (right part) along the green lines overlaid on different cross-shaped species in the STM images (left part). The three blue dotted lines are given as reference to find the full width at half maximum (FWHM) (the center dotted lines) of the peak. The peak position is defined as the center of the FWHM (black vertical lines).

4) Structure Confirmation of Gd-SNPc by Size Comparison
According to the distance (21.2 ± 0.2 Å, green line, Supplementary Figure 4a) between two opposite tetramethyl-cyclohexane moieties of the Fe-NPc molecule, the distances between the Fe center and the tetramethyl-cyclohexane is derived to be 10.6 ± 0.1 Å. Considering that the N-Gd bond length (2.7 ± 0.5 Å) 2 is about 0.6 Å larger than the N-Fe bond length (2.1 ± 0.5 Å), 3 the distance between Gd and the tetramethyl-cyclohexane moiety in Gd-SNPc is calculated to be 11.2 ± 0.1 Å (Supplementary Figure 4b, red lines). Therefore, the distance between two farthest tetramethyl-cyclohexane moieties in the five-fold symmetric Gd-SNPc molecule is derived to be 21. . Black spheres represent carbon atoms; blue, nitrogen; white, hydrogen; red, iron; pink, gadolinium.

6) Orientation of a Polycyanine Chain with Respect to the Ag(111) Surface Lattice
The chains extend along the high-symmetry directions of the substrate and have a periodicity of three times the Ag(111) surface lattice constant, i.e., they are commensurate with respect to the substrate. Direct evidence for this is the high-resolution STM image (Supplementary Figure 6)      Bonding analysis was performed at PBE-D3(BJ)/DZP with different k space samplings, using pEDA. 4 The pEDA method allows to dissect the interaction energy between two fragments (here: molecule and surface) into well-defined quantities that allow to interpret the bonding in a system in a chemically meaningful way. The interaction energy (E int ) is first divided into a dispersion term (Edisp) and an electronic term (Eelec). The actual pEDA procedure then decomposes E elec into contributions from Pauli repulsion (EPauli), electrostatics (Eelstat) and orbital interaction (Eorb): This enables a quantitative analysis of the surface-adsorbate bonding. is calculated with a projection of plane waves 5 onto an atom-centered def2-TZVP basis set. 6 Averaged positions for distance of the N atoms in the ring (Nring) and the aza-bridging N atoms (N bridge ) with respect to the non-corrugated surface plane are shown. The adsorption energy term (E ads ) is dominated by dispersion interactions (E disp = -412 kJ mol -1 ) and shows repulsive electronic interactions (Eelec = +34 kJ mol -1 ). The butterfly angle  is defined as an inter-plane angle between the planes spanned by the atoms highlighted in yellow of the two pyrrole rings A and B, respectively.
Supplementary Table 2. Structural parameters of the polycyanine chain free-standing and adsorbed on Ag(111). Definition of angle γ and inter-plane angle α as shown in Supplementary  Figure 11, lattice parameter in chain direction. [a] the lattice mismatch amounts to 0.4%. S12

12) Origin of the Unusual Bending Angle of the Polycyanine Chain
The polycyanine chain is not planar, but has an intrinsic bending angle, which is also present in the gas phase calculations. In the following, we will elucidate whether this bending angle is of electronic origin, steric origin, or both. This will be done by using a range of model systems (M1-M8 in Supplementary Figure 12, Supplementary Figures 13 and 14) in which the -electronic structure and the amount of steric hindrance are systematically varied by substitution or exchange of groups. Saturation of half of the N atoms in the pyrrole rings (Nring) (M2) reduces bending to 126.62°. The steric repulsion of the N lone pair and -CH in the six-membered "open" ring of M1 is apparently not causing the bending. Instead, it may be of electronic origin. This is indicated by the model system (M3), in which all N atoms in the pyrrole rings (N ring ) are saturated. As a result, the bending angle further decreases. Some H-H repulsion prevents an angle of 180°. Removing the H-H repulsion (M4) leads to a perfectly coplanar arrangement. The same is achieved with an all carbon chain (M5). Since isoelectronic substitution does not change the number of π-electrons, another electronic effect must be present. Similarly, saturation of the periphery (M6) only increases the angle to 133.8°. Therefore, the bending effect must be an intrinsic property of the backbone chain. Saturation of the aza-bridging nitrogen (N bridge ) (M7) also results in coplanar arrangement. This is also the case for a larger model system based on M7 (Supplementary Figure 13) containing an additional annulated benzene ring in order to include possible steric repulsion (or, alternatively, CH … N hydrogen bonding) effects between hydrogen on this benzene ring and the lone pair on the N atom in the pyrrole ring (Nring). However, this extended model system also shows coplanar arrangement. Therefore, steric repulsion is ultimately ruled out as the cause of bending. Instead, the conjugation of the N lone pairs with the π-systems of the chain and the periphery, which emerges as a consequence of the specific arrangement of N and C atoms found in the polycyanine chain, remains as the most probable explanation. Furthermore, adding another imine to the periphery (M8) decreases the angle to 106.9°, the most bent structure in this set. The larger the electron deficiency is in the π-system, the larger is the stabilization by conjugation. For this reason, saturation with H decreases the bending angle, while adding more electronwithdrawing N atoms increases it. Supplementary Figure 15 shows a magnified version of the frontier orbitals HOCO-2 and HOCO-3 of polycyanine from Figure 5. The conjugation of the N-lone pairs with the π-system of the backbone and the periphery is clearly visible. Even for a very small model system (M9, Supplementary Figure 14), the bending is found. In the case of this model, we use the dihedral angle  <(N-C-N-C) to describe the bending since a second ring is not available for the definition of  in the same way as done in the original system. For this model system, we can set up a Walsh diagram (Supplementary Figure 16) showing the orbital shape and energies for different dihedral angles . In can be clearly seen that upon increasing the dihedral angle from 0° to the structural minimum of 46° the HOMO-3 representing non-bonding electron pair conjugation is strongly stabilized while the conjugation (orbitals HOMO, HOMO-1, HOMO-4) is decreased by a similar but slightly smaller amount. This intrinsic bending thus stems mostly from the increased conjugation of the non-bonding electron pair at nitrogen. Noteworthy, to achieve more accuracy of the models in Supplementary Figure 12 and Supplementary Figure 13, we reproduced the GGA results with a range-separated hybrid functional (HSE06) and see the same trends (see the comparisons in Supplementary Figure 12

14) Optimized Structures in VASP Format
The optimized atomic structures can be found in the NOMAD repositories