Fine‐Tunable Electronic Energy Levels of Mixed‐Metal Prussian‐Blue Alloy Nanoparticles

Abstract A specific electronic interaction among metal ions emerges in solution‐processed films of coordination polymer (CP) nanoparticles (NPs). The most classic CP, Prussian blue (PB), is alloyed with Ni to form Fe_xNi_3−x[Fe(CN)₆]₂ showing an identical X‐ray crystallographic phase in all composition ratios of 0≤x≤3. By surface modification using [Fe(CN)₆]⁴⁻, the PB alloy NPs are dispersed into water, and spin‐coated films of the NPs adhere to indium‐tin‐oxide substrates via a low‐temperature heating process at 100 °C. It is revealed that systematic fine tuning of the electronic energy levels is optically and electrochemically possible in the films by controlling the composition ratios. This is possible due to the d(t_2g)–π*(C≡N⁻) electronic conjugation among three redox‐active iron species, Fe^II−C≡N, Fe^III−C≡N, and Fe^III−N≡C, which coexist by alloying with Ni. The heating process conducts the restoration of discontinued d–π* bonding networks among the NPs.