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-C₈) as the π-conjugated organometallic molecule, tungsto(molybdo)phosphoric heteropolyacids HPA (HPA = H ₃PMo₁₂O₄₀, H₃PW₁₂O ₄₀, H₆P₂:-Mo₁₈O₆₂, 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 π-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-C₁₆) and the periodicity of the layered structure for the OMA-C₁₆/ODA/H₃PMo ₁₂O₄₀ LB film is ca. 3.7 nm. Luminescence spectra of hybrid LB films show that HPA can quench the emission of OMA-C₁₆ and OMA-C₈ to some extent. These LB composites show good photovoltage responses and a photovoltage of 103 μV 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.