Hybrid organized molecular films composed of a polyoxometalate, decatungsteuropate (EuW(10)), and amphiphiles such as hexadecyltrimethylammonium bromide (CTAB), n-octadecylamine (ODA) and 4-hexadecylaniline (HDA) were fabricated by Langmuir-Blodgett (LB) technique and their photoluminescent properties were investigated. The hybrid films, which were formed through in situ complex formation at the air/water interface and subsequently transferred onto the solid substrate, were characterized by UV-vis, FT-IR, fluorescence, and AFM measurements. The transferred hybrid films showed red emission characteristic of the Eu(III) ion upon UV irradiation. The photoluminescence of the hybrid films was sensitive to the acid and base gases. When ODA/EuW(10) and HDA/EuW(10) hybrid films were exposed to HCl gas, their photoluminescence disappeared completely. Interestingly, the photoluminescence was recovered upon subsequent exposing the same film to NH(3) gas. Such process could be repeated many times and a switch based on these hybrid films was proposed. On the other hand, the photoluminescent intensity of CTAB/EuW(10) film decreased but never disappeared upon exposing to HCl gas. Similarly, the photoluminescence could also be partially recovered upon exposing to NH(3) gas. Detailed investigation on the spectral changes of the films revealed that the interaction between EuW(10) and CTAB and was different from EuW(10) with ODA or HDA, and protonation of amine group in ODA or HDA induced by HCl gas played an important role in realizing the "on" and "off" photoluminescence switch of the hybrid films.
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