Following the optimized route P3, AuNP-3 and AuNP-4 were synthesized using precursors 1' and azide containing 2'. The absence of the imidazolium proton (C 2 H) in the 1 H-NMR spectra in combination with the appearance of the C 2 signal at 184.0 ppm in C NMR indicated the successful carbene formation (Figure ). All other NMR signals can be assigned to the remaining structure of the NHC anchor. Subsequently, FT-IR measurements of thin films of AuNP-3 and AuNP-4 show the absence of the imidazolium ring stretch (N 1 -C 2 -N 3 ) signal at 1570 cm -1 , underlining the successful installation of NHCs on the AuNPs surface. In the case of AuNP-4 the IR band associated with the terminal azido groupwhile compared to the employed 2' precursorremained intact (for comparison see ESI, Figure ). XPS analysis of obtained AuNPs confirms the structural features identified in previous analyses and is consistent with previously reported data by Nazemi, Crudden, and coworkers. C 1s scans show contributions of C-C/C-H as well as the PEG-associated C-O-C ether bonds at 284.8 eV and 286.4 eV, respectively (see ESI for XPS spectra, Figure -14). Comparing XPS spectra of PEGylated AuNPs and their precursor OAm@AuNP, distinct differences in the N 1s and Au 4f scans are observable, indicating successful NHC anchoring to the AuNP surface. The observed peak in the N 1s scan of AuNP-3 and AuNP-4 can be separated in the N-C 2 structure associated with the NHC(C 2 )-AuNP bond and the quaternary N (N 1/3 =C) contributions from the nitrogen connecting the NHC wingtips at 400.4 and 399.1 eV. Distinct contributions of the azido group at ~405 eV in AuNP-4 were not detectable due to the lability of the azide groups during XPS measurements (Figure ). High-resolution Au 4f scans show Au(0) and Au(I) contributions (see Figure ), similar to previously reported XPS data obtained from bottom-up synthesized NHC@AuNPs. Observed peaks at 88.3 and 84.6 eV in the case of AuNP-3 suggest the presence of Au(I), as they are shifted by ∆BE = 1.2 eV compared to Au(0) components (Au 4f5/2 87.1 eV and Au 4f7/2 83.4 eV; see ESI for detailed comparisons, Figure ). Interestingly, the presence of Au(I) suggests that during ligand exchange, the NHC coordinates onto the Au surface oxidatively, generating partially oxidized Au surface atoms or Au ad-atoms like that observed during the coordination of NHC-CO2 adducts to Au(111) surfaces in previous reports. Such an 'oxidative' ligand exchange on AuNPs is -to the best of our knowledge -not reported for commonly used surface chemistry (e.g. amine or thiol based ligands).