Synthesis of Novel Ruthenium‐Polymetallaynes and Their Application in Multistate Electrochromic Memory

Multilevel (or multistate) electrochromic devices have the potential to achieve highly compact memory capacity while instantaneously transferring data between memory and processing units. In this article, three novel solution‐processable ruthenium‐polymetallaynes (i.e., P1, P2, and P3), in which the redox‐addressable Ru center is covalently embedded into a conjugated organic polymer, are discussed. In pursuit of higher functionality (e.g., stable multistate behavior, low operating voltage), the organic ligand bridging the metal centers is systematically varied. The previously reported P1 has a bithiophene (BT) bridging ligand with a high degree of rotational freedom. By replacing BT with cyclopenta‐dithiophene in P2 and dithieno‐pyrrole (DTP) in P3, both of which are more planar than BT, the degree of freedom is decreased. By using DTP, redox‐matching is achieved between the metal center and organic ligand, leading to extra stability of the mixed‐valence (MV) state in P3. In‐depth experimental (i.e., in situ electron paramagnetic resonance and UV–vis–NIR spectroelectrochemistry) and theoretical studies (i.e., DFT calculations) are carried out on the polymer thin‐films, showing enhanced metal–metal (M–M) interaction in P2 and P3 and stable Robin–Day class III MV compound in P3. These polymers are also first time fabricated into solid‐state electrochromic devices and the stability of each oxidation state is characterized by tracing the change of transmittance over time, showing satisfactory cyclic stability and retention behavior (≈90% retention after 30 min). Three novel Ru‐polymetallaynes with different organic linkers are synthesized. By introducing bridging ligand rigidity and redox‐matching, mixed‐valence species are formed as suggested by experimental (SEC, in situ EPR) and theoretical (DFT) results. In electrochromic devices, the enhanced metal–metal interaction and resonance stabilization lead to significantly improved optical memory properties (i.e., cyclic stability and state retention).