## 2 Computational Methodology  
The structural and electronic properties of the metal-SAM interfaces were simulated by density functional theory (DFT) employing the all-electron, full potential FHI-aims code (version 190715 [91; 92; 93; 94; 95] (see also aimsclub.fhi-berlin.mpg.de) and periodic boundary conditions. The Perdew-Burke-Ernzerhof (PBE) [96; 97] functional was used for describing exchange and correlation. Furthermore, long-range van der Waals interactions were accounted for by employing the surface version [98] of the Tkatchenko-Scheffler dispersion correction [99], which was specifically parameterized for treating adsorbing molecules on metal substrates. The dispersion correction between the Au atoms of the metal slab was turned off. All calculations were done with the so-called tight basis set for all atomic species (as supplied by FHI-aims). A thorough description of the corresponding basis functions is included in the Supplementary Materials. Reciprocal space was sampled by a converged \(\Gamma\)-centered \(15\times 10\times 1\) grid for the full coverage systems and by accordingly smaller sized grids for larger super cells. The change of the volume-integrated electron density was converged to \(10^{-5}\) e\({}^{-}\) and the total energy to \(10^{-6}\) eV. Interfaces were modeled employing the repeated-slab approach with the Au(111) substrate represented by five metal layers. The bottom three Au layers were kept fixed in all calculations to avoid spurious relaxations at the bottom surface. The periodic replicas of the slabs were quantum-mechanically and electrostatically decoupled by a vacuum gap of more than 20 A and a self-consistent dipole correction [100; 101]. The geometries of the adsorbate molecules and the top two Au-layers in the full coverage unit cells were fully relaxed until the remaining forces on each atom were below \(10^{-3}\) eV/A. The geometries of the other supercells considered here were directly derived from the full coverage unit cell by replicating it in \(x\)- and \(y\)-directions and removing all but one molecule from the resulting cell (see Supplementary Materials). These supercells were considered as model systems to study the impact of diluting the interfacial dipoles. Thus, we fixed the remaining molecule in the geometry it adopts in the densely packed layer to prevent it from falling over [102]. The change of the work function was obtained from the difference of the calculated work functions at the bottom side of the Au(111)-slab (\(\Phi_{\text{Au}}=5.10\) eV for all systems) and above the self-assembled monolayer. Furthermore, the work function change of the nominally non-interacting system, i.e., the SAM without a docking group moved 1 A away from the substrate compared to its equilibrium adsorption distance (see Section 3.2), was defined as a reference point relative to which the work function changes (\(\Delta\Phi\)) for all other systems are reported. The difference between lower and upper slab work function for the reference system amounts to \(\delta\Phi_{\text{ref}}=-0.11\) eV. The core level binding energies were calculated using the initial state approach, relying on the Kohn-Sham eigenvalues of the respective orbitals. This approach does not provide absolute values of the core level binding energies, but yields relative shifts between different systems [65; 68; 103; 104; 105; 106; 107; 108]. We have also found it to provide a very good description of core level shifts in SAMs [21; 22; 48; 49; 63; 64]. In fact, when modeling the X-ray photoelectron (XP) spectra of (partially) aromatic hydrocarbon SAMs bonded to Au substrates, we typically find that shifting the calculated spectra to higher binding energies by between 18.9 to 19.0 eV [22; 49; 90; 109] yields an excellent correlation with experimental data.