Dual Redox-Responsive Os/Ru-Based Alternated Heterobimetallic Supramolecular Polymer as a Multicolor Electrochromic Material for Camouflage Devices

Abstract

Materials that show multicolor electrochromism, including yellow and green, are highly applicable for various smart applications including voltage-tunable multicolor electrochromic (EC) displays and camouflage devices. Although metallo-supramolecular polymers (MSPs) show excellent EC color variability with attractive EC properties, the generation of multicolor electrochromism from one MSP is still difficult. Moreover, an MSP-based multicolor EC device (ECD) that also exhibits yellow and green EC colors has not been realized to date. Herein, we report the synthesis of a dual redox-responsive heterobimetallic supramolecular polymer (PolyOsRu) as a multicolor EC material that can also be used for camouflage applications. PolyOsRu was synthesized by stepwise homoleptic complexation of Os2+ and Ru2+ ions using a 2,2′:6′,2″-terpyridine-based ligand and characterized by various analytical and spectroscopic techniques. The polymer shows broad absorption (312–671 nm) and well-separated dual redox potentials of Os2+/Os3+ (E1/2 = 0.59 V) and Ru2+/Ru3+ (E1/2 = 0.93 V) pairs. A thin film of PolyOsRu on ITO displays reversible multicolor (brown–red ↔ yellow ↔ green) electrochromism with a maximum optical contrast of ∼58%, fast EC color switching (<1 s), a good coloration efficiency of 404.39 cm2/C, and a more than 2400 EC cycling stability. Finally, the fabrication of a solid-state ECD and a prototype EC camouflage display with the polymer film is demonstrated to represent its potentiality as a multicolor EC material for display and camouflage applications.