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

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 x Ni 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.