Layer-by-layer assembly of multilayer films of polyoxometalates and tris(phenanthrolinedione) complexes of transition metals

A series of organic–inorganic composite films were prepared by the layer-by-layer self-assembly method containing the phendione complexes of transition metals [M(phendione)3]2+ (M=Fe2+, Co2+, phendione=1,10-phenanthroline-5,6-dione) and the polyoxometalates (POMs). UV–vis spectroscopy was used to follow the fabrication process of (BW12/[M(phendione)3]2+)n (BW12=BW12O405−, M=Fe2+, Co2+) and (Co4(PW9)2/[M(phendione)3]2+)n (Co4(PW9)2=Co4(H2O)2(PW9O34)210−, M=Fe2+, Co2+) multilayer films. Electrochemical studies on the films illustrate that the POM species exhibit well-defined redox peaks and the phendione species show pH-dependent electrochemical behavior. The photoluminescent properties were investigated to show the (BW12/[Fe(phendione)3]2+)n film with low-energey red photoluminescence at 672 nm.