Multicolor electrochromic ultrathin films based on neutral red and polyoxometalate

Electrochromic ultrathin films composed of the polyoxometalate cluster K₁₀P₂W₁₇O₆₁]·17H₂O (P₂W₁₇), polyallylamine hydrochloride (PAH) and Neutral Red (NR) were fabricated on quartz, silicon wafer and indium-tin oxide substrates by the layer-by-layer self-assembly method. The multilayer P₂W₁₇/PAH/P₂W₁₇/NR]_n films were characterized by UV-vis spectroscopy, scanning electron microscopy, cyclic voltammetry and chronoamperometry and in-situ spectral electrochemical measurements, which exhibited suitable response time, high optical contrast and low operation potential. The monolacunary polyoxometalate-based electrochromic film displays adjustable colors and undergoes transitions from deep pink to light purple, then to dark purple-blue over the potential range from +0.2 V to − 1.0 V. Furthermore, two types of data storage using optical changes of the P₂W₁₇/PAH/P₂W₁₇/NR]₃₅ film are proposed. The results provide valuable information for exploring applications in tunable-color electrochromic devices and data-storage devices.