Chiral Organization and Charge Redistribution in Chloroaluminum Phthalocyanine on Au(111) Beyond the Monolayer

Abstract

The non-trivial effect of molecular dipoles on the surface work function of metals is explored for the unidirectional ordered arrays forming the first and second layers of chloroaluminum phthalocyanine (ClAlPc) on Au(111). This phthalocyanine is a non-planar molecule with permanent electric dipole perpendicular to its molecular π-plane that can adopt two distinct configurations (Cl-up and Cl-down) when adsorbed on surfaces. The ordered array forming the first layer is known to consist of all Cl-up molecules, while the less studied second layer is formed by molecules in the Cl-down configuration. The inverted orientation of the molecules in these two layers constitutes our benchmark system to investigate the influence of the dipole array orientation on the surface work function. The present study includes an 2 experimental and theoretical approach that combines diverse imaging and spectroscopic scanning probe microscopies, in ultra-high vacuum, with first-principles DFT-based atomistic simulations.Experiment and theory show a chiral organization transferred from the first layer to the growing film that is reflected in the electronic structure. We demonstrate that the obtained surface work function changes are smaller in magnitude than expected from a dipolar approximation due to charge rearrangement at and beyond the monolayer. We provide understanding of the crucial interplay between the inter-layer and organic-metal interactions and quantify their effect on the electron density distribution and on the work function changes.

Submolecular Imaging of Parallel Offset π–π Stacking in Nonplanar Phthalocyanine Bilayers

“…The most stable stacking geometry is depicted in Figure 3d, in which the yellow molecule represents the face-down adsorbed second-layer ClAlPc. The calculated interlayer distance (h) is 2.9 Å, matching well with the measured line-profile of ClAlPc on Au(111) (Figure S3), and is also consistent with the previously reported height of second-layer nonplanar Pc on graphite, 23 Au(111), 22 and Ag(111), 26 thus validating the reliability of the model. The inset in Figure 3e distinctly reveals the stacking geometry of the outmost benzene rings in the two layers, with rotation angles of 0, 15, and 30°, respectively.…”

“…In this work, we employ two typical nonplanar phthalocyanine (Pc) molecules, vanadyl phthalocyanine (VOPc) and chloroaluminum phthalocyanine (ClAlPc) with central O−V and Cl−Al lying orthogonal to the molecular plane, 15,30 main advantages. First, the hollow site among four Pc molecules in the densely packed first layer provides the only anchoring site for the second-layer molecules with face-down configuration (O or Cl atom pointing towards the substrate), 22 so that interlayer stacking (rotation angle) is solely dominated by the π−π interaction between the outmost benzene rings in the two layers, in addition to the intermolecular dipole−dipole interaction. This feature is of vital importance to precisely define the arrangement of benzene rings compared with other aromatic molecules, such as planar Pc or porphyrins 11,31 with parallel offsets varying from each other.…”

Probing the Properties of Quasi‐Isolated ClAlPc by Using Polycrystalline h‐BN on Pt(111) as a Testbed

“…It is generally accepted in the literature that the ClAlPc molecules with a Cl-up configuration are imaged having a central protruding dot, which is related to the chlorine atom, whereas such feature is absent when the molecules adsorb with a Cl-down configuration. [8,10,12,[14][15][16]18,[22][23][24] Based on this argument, the submolecular features observed at the bottom part of Figure 3b could be ascribed to ClAlPc units in a Cl-up configuration, and these at the upper part, to molecules with the Cl atom pointing down. Then, the apparent height differences between molecules with these two orientational configurations (see Figure 3c) point toward that ClAlPc molecules deposited on h-BN/Pt(111) at RT form primarily bilayer structures, where the molecules in the first and second layer adopt a Cl-up and Cl-down configuration, respectively (see the insets in Figure 3c).…”

“…A particular system is Gr/Pt(111), [16] where the as-grown samples form preferentially MLs in which all the molecules always adopt a Cl-up configuration. In contrast, on noble metal substrates, [14,[17][18][19][20][21][22][23][24] ClAlPc molecules interact stronger with the support, and molecules with Cl-up or Cl-down configuration are commonly found to coexist within the as-grown MLs, although upon annealing, single layers with molecules in a Cl-up configuration can be obtained. The interaction with the substrate also influences the electronic structure of ClAlPc.…”

Binding and Electronic Level Alignment of $\boldsymbolπ$-Conjugated Systems on Metals

“…Similar symmetry reductions have been observed also for other Pcs on different substrates, e.g., for CuPc on Cu(111) 526 and on Ag(100) 527 , for FePc on Cu(111) 528 and for PtPc as well as PdPc on Ag(111) 529 . In general, both orientations (Cl-up or Cl-down) have been observed for vacuum-sublimed ClAlPc on the (111)surfaces of noble metals 505,506,523,530 . Moreover, the orientation can be changed by, e.g., the deposition rate 506 , post-deposition annealing 505 or by pulsing using an STM tip 531 and can thus act as molecular switches 531,532 .…”