Dual Redox-Responsive Os/Ru-Based Alternated Heterobimetallic Supramolecular Polymer as a Multicolor Electrochromic Material for Camouflage Devices
Sanjib Sarmah, Siddhartha Shankar Kashyap, Manas Kumar Bera
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 Os 2+ and Ru 2+ 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 Os 2+ /Os 3+ ( E 1/2 = 0.59 V) and Ru 2+ /Ru 3+ ( E 1/2 = 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 cm 2 /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.