Electrochromic multilayer films of tunable color by combination of copper or iron complex and monolacunary dawson-type polyoxometalate

Electrochromic multilayer films consisting of polyoxometalate (POM) cluster α-K₁₀[P₂W₁₇O₆₁] ·17H₂O (P₂W₁₇), copper(II) complex [Cu^II(phen)₂](NO₃)₂ (phen = 1,10-phenithroline), and iron complex [Fe^II(phen)₃] (ClO₄)₂ were fabricated on silicon, quartz and ITO substrates by layer-by-layer self-assembly method. The multilayer films, PSS/Cu^II(phen)₂/[(P₂W₁₇/Cu ^II(phen)₂)]_n and PSS/Fe^II(phen) ₃)]_n were characterized by UV - vis spectra, X-ray photoelectron spectra, cyclic voltammetry (CV), chronoamperometric (CA) and in-situ spectral electrochemical measurements. The interesting feature of the electrochromic film is its adjustable color by reduction of both transition metal complex and polyoxometalate at different potentials. The multilayer films also exhibit high optical contrast, suitable response time and low operation potential due to the presence of mono-lacunary-substituted polyoxometalate and transition metal complex. This is the first example that the color of electrochromic film can be adjustable, which gives valuable information for exploring new electrochromic materials with tunable colors.