Four photoelectroactive composite films based on [BW11O39M(H2O)]7− (M = Zn, Cu) and bipolar hemicyanines

Abstract

Four composite films consisting of Zn(II) and Cu(II) substituted tungstoborates K7[BW11O39M(H2O)] (BW11M, M=Zn, Cu) and two bipolar hemicyanines of (E)-1,1′-(propane-1,3-diyl)bis(4-(4-(dimethylamino)styryl)pyridinium) bromide (H3Br2) and (E)-1,1′-(decane-1,10-diyl)bis(4-(4-(dimethylamino)styryl)pyridinium) bromide (H10Br2), were prepared by electrostatic layer-by-layer self-assembly technique. These films of (BW11M/Ha)n (M=Zn, Cu; a=3, 10) exhibited ultraviolet-visible characteristic absorption bands of BW11M and HaBr2 with their absorption intensities increasing linearly with increasing the layer number n, indicating that the composite films were successfully and uniformly deposited. With respect to the H3Br2 and H10Br2 aqueous solutions, the intramolecular charge transfer absorption bands of H3Br2 and H10Br2 in the films exhibited bathochromic shifts to different extents depending on the hemicyanines and BW11M in the films. These films could generate stable, cathodic photocurrents with photocurrent action spectra being consistent with corresponding absorption spectra of the hemicyanines in the films, when illuminated with 100mW/cm2 polychromatic light (730nm>λ>325nm). The effects of the alkyl chain length, BW11M, layer number of the (BW11M/Ha)n films, and applied bias potential and electron acceptor in the electrolyte solution on the photocurrent densities are discussed.