Electrochromic metallo-supramolecular polymers showing visible and near-infrared light transmittance modulation
Metallo-supramolecular polymers (Fe-MEPEs) based on Fe2+ ions and bis(terpyridine) ligands exhibit outstanding optical and electrochromic properties. The intensive coloration of Fe-MEPEs is caused by the metal-to-ligand charge transfer (MLCT) transition in the visible region. Thin films with high optical quality can be produced on transparent conducting glass or plastic substrates by common wet-coating techniques, e.g. dip-coating or roll-to-roll (R2R) processes. By applying a low voltage, the Fe-MEPE films can be reversibly switched between the reduced (dark) state (Fe2+) and the oxidized (bright) state (Fe3+). A further color change is visible at negative voltages resulting from a strong absorption in the near-infrared (NIR) region. Visible light transmittance changes (Dtv) > 60%, fast response times, and cycle stabilities over 10,000 switching cycles are demonstrated, which makes these electrochromic Fe-MEPEs very attractive to be used in electrochromic devices for a number of applications, e.g. in wearables, labels, architectural glazing, appliances, vehicles, and aircraft.