Photoelectrochemical properties of three inorganic/organic hybrid films formed from sandwich-type tetrazinc(II) tungstophosphorate and hemicyanines with varied alkyl chain lengths

Three inorganic/organic hybrid films consisting of sandwich-type tetrazinc(II) tungstophosphorate [P2W18Zn4(H2O)2O68]10− (P2W18Zn4) and three hemicyanines of (E)-1,1′-(propane-1,3-diyl) bis (4-((E)-2-(4-(dimethylamino) naphthalen-1-yl) vinyl)-pyridinium) bromide (N3), (E)-1,1′-(hexane-1,6-diyl) bis (4-((E)-2-(4-(dimethylamino) naphthalen-1-yl) vinyl) pyridinium) bromide (N6), and (E)-1,1′-(decane-1,10-diyl) bis (4-((E)-2-4-(dimethylamino) naphthalen-1-yl) vinyl) pyridinium) bromide (N10), were prepared by electrostatic self-assembly technique. The UV–visible spectra showed that three inorganic–organic hybrid films of P2W18Zn4/Na (a = 3, 6, 10) were uniformly deposited and the hemicyanine molecules formed J-aggregations in the films. The monolayer (P2W18Zn4/N3,6,10)1 films exhibited stable, large cathodic photocurrent densities of 1.41–4.62 μA/cm2 that strongly depended on the alkyl chain lengths, while irradiated with 100 mW/cm2 polychromatic light of 730 nm > λ > 325 nm at an applied potential of −0.3 V vs. saturated calomel electrode. The photocurrent action spectra indicated that the cathodic photocurrents were generated by the charge transfer excitation of the hemicyanines in the films. The effects of applied bias voltages, electron acceptor added into the electrolyte solution, and layer numbers of the (P2W18Zn4/Na)n films on photocurrent generation of (P2W18Zn4/Na)n film were also examined.