Near‐Infrared Electrochromism Based on Intervalence Charge Transfer

Near-infrared (NIR) electrochromic materials (ECMs) are specific ECMs featuring in the modulation of NIR (750–2500 nm) light absorptions and are potentially useful in civil and military products, such as “smart windows” for thermal control, NIR photodetectors, bioimaging, fiber optic communications, and military camouflage. In addition, ECMs have been applied to optical memory storage and molecular logic operation, taking advantage of their optical memory effect. Some transition metal oxides, organic small molecules, metal complexes, conducting polymers, and emerging covalence-organic framework materials with redox properties or electron “donor-bridge-acceptor” structures are potential NIR ECMs. Generally, the NIR electrochromic properties come from the intramolecular intervalence charge transfer of these materials in the singly oxidized or reduced state. NIR ECMs cover inorganic, organic, and organic–inorganic hybrid materials. In this chapter, the emerging NIR ECMs and their electrochromic properties and mechanism are surveyed.