Langmuir-Blodgett films of heteropolyoxometalate/organomercury acetylide hybrid composites: Characterization and photoelectric properties

A new family of organometallic/inorganic nanohybrid Langmuir-Blodgett (LB) films consisting of rigid-rod organomercury acetylide complex (OMA-C-16 or OMA-C-8) as the pi-conjugated organometallic molecule, tungsto(molybdo)phosphoric heteropolyacids HPA (HPA = H3PMo12O40, H3PW12O40, H6P2Mo18O62, or H6As2W18O62) of the Keggin and Dawson structures as the inorganic component, and octadecylamine (ODA) as the auxiliary film-forming agent were prepared and characterized by pi-A isotherms, UV-vis absorption spectra, fluorescence spectra, atomic force microscopy imaging, scanning tunneling microscopy, surface photovoltage spectroscopy, and low-angle X-ray diffraction. Our experimental results indicate that steady, even, and ordered Langmuir and LB films are formed in pure water and heteropolyacid subphase. They typically have a highly organized lamellar structure in which a monolayer of HPA is arranged alternately with well-ordered layers of OMA (and also ODA for OMA-C-16) and the periodicity of the layered structure for the OMA-C-16/ODA/H3PMo12O40 LB film is ca. 3.7 nm. Luminescence spectra of hybrid LB films show that HPA can quench the emission of OMA-C-16 and OMA-C-8 to some extent. These LB composites show good photovoltage responses and a photovoltage of 103 mu V can be obtained for the OMA-C-16/ODA/H3PMo12O40 system when it is excited by light at 330 nm. The monolayer LB films on silica wafer can also display interesting electrical conductivity behavior.