Preparation, luminescence and photoelectric properties of Langmuir-Blodgett films of alkynylplatinum(II)-zinc(II) porphyrinate/heteropolyoxometalate hybrid composites

A new class of organometallic/inorganic hybrid Langmuir-Blodgett (LB) films, consisting of rigid-rod alkynylplatinum(II)-zinc(II) porphyrinate complex (OMA) as the π-conjugated donor-acceptor-type molecule and tungsto(molybdo)phosphoric heteropolyacids (HPA) (HPA = H₃PMo ₁₂O₄₀ and H₃PW₁₂O₄₀, abbreviated as HPMo₁₂ and HPW₁₂, respectively) of the Keggin structure as the inorganic component, were prepared and characterized by π-A isotherms, UV-vis absorption and luminescence spectra, low-angle X-ray diffraction, scanning tunneling microscopy and surface photovoltage spectroscopy. Our experimental results indicate that stable, well-defined and well-organized Langmuir and LB films have been formed in pure water and heteropolyacid subphase. They typically have a highly organized lamellar structure in which a monolayer of HPA is most likely embedded inside the OMA molecular space formed by long chains of PBu₃. Luminescence spectra of these hybrid LB films show that HPMo₁₂ and HPW₁₂ can enhance the emission of OMA to some extent. These LB composites show good photovoltage responses and a photovoltage of 79 μV can be obtained for the OMA/HPMo₁₂ system when it is excited by light. The monolayer LB films on ITO wafer can also display interesting electrical conductivity.