To better understand the coupling between PS and POM-PtCl and its effects on the electronic properties of the system, first principles simulations using spin-polarized density functional theory (DFT) calculations within the ORCA program package. Initial geometry optimization used the PBEh-3c composite method followed by geometry optimizations with the PBE0 hybrid functional and a def2-TZVP basis set. For molybdenum and iridium, effective core potentials were used to replace the core electrons. Dispersion interactions were accounted for by atom-pairwise correction with the Becke-Johnson damping scheme [D3(BJ)]. The conductor-like polarizable continuum model (CPCM) was used to implicitly include the DMF solvent (𝜀=38.30 and 𝑛=1.43). Electron densities were analyzed by Hirshfeld population analysis to determine atomic charges. To gain insights into the energetics and binding behavior of PS and POM-PtX, we used DFT calculations to assess the interaction energies between both species. As model systems, we focused on PS (charge: 1+) and POM-PtCl (charge: 3-), see Figure . As references, we studied [Pt(bpy)Cl2] (charge-neutral) and the TRIS-functionalized prototype Anderson anion [MnMo6O18{(CH2O)3CNH2}2] 3-(POM-Ref, charge: 3-, SI, Figure ). Initial studies gave interaction energies of -48 kJ/mol (PS / [Pt(bpy)Cl2]) and -76 kJ/mol (PS / POM-ref) and -77 kJ/mol (PS / POM-PtCl), respectively. This highlights, that supramolecular aggregation in solution between photosensitizer and POM is thermodynamically favored. For the PS / POM-PtCl system, we observe that in the energetically most favored system, PS is located next to the metal oxo cluster (Figure ), highlighting the importance of the POM for PS-binding. Note that quantitatively virtually identical results were obtained for POM-PtI; these are shown in the SI, Section 8). The iso-surfaces correspond to electron-accepting regions where an additional added electron will be located (as indicated by the 𝑓 + Fukui function). Regions with higher values are marked in darker shades of green. Molecular colour scheme, see Figure .