Triple-Band Electrochromic Switching Among Visible (400–750 nm), NearIR-I (750–1000 nm), and NearIR-II (1000–1600 nm) Regions with Triple-Redox-Active Metallosupramolecular Polymers

Selective electrochromic (EC) switching in the wide range from visible (VIS) to near-infra-red (NIR) wavelengths was achieved using novel triple-redox-active metallosupramolecular polymers (MSPs), synthesized by 1:1 complexation of a transition metal salt and a bisterpyridine ligand containing a tetraphenylbenzidine (TPB) moiety. By tuning an oxidation potential in the range between 0 V and 1.2 V vs. Ag/Ag+, the MSPs (polyFeLTPB and polyRuLTPB) were capable of selective and reversible triple-band EC modulation in the visible (400–750 nm), NIR-I (750–1000 nm), and NIR-II (1000–1600 nm) regions. Interestingly, the polymers exhibited excellent EC properties with remarkably high optical contrast (98%), high coloration efficiency (CE) (851 cm2/C), and fast switching even in the NIR region. A made-to-order quasi-solidstate EC device exhibited exceptionally long cycle stability (>7000 cycles) from the visible to the NIR region at an incredibly low operational voltage (1.2 V). These two ECDs demonstrated that a significant amount of solar irradiance (about 33–36%) shielding in the NIR band at 750–1670 nm while allowing 46–53% of VIS transparency under low voltage. At dark mode at 0.8 V, they exhibit 59–63% of VIS and 45–47 % NIR blocking. Under full oxidation, ECDs screen 51–60% VIS and 36–41% NIR while using very small electrical energy (about 1.7–13.5 mJ cm–2). These findings signify a significant advancement in the design of large scalable dual-band EC devices.