Multicolor electrochromic ultrathin films based on neutral red and polyoxometalate

Electrochromic ultrathin films composed of the polyoxometalate cluster K10[P2W17O61]·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.