Complexation of Metal Ions with Amphiphilic o,o'-Dihydroxyazobenzene Derivatives at the Air/Water Interface

The effect of metal salts (FeCl3, FeCl2, CuCl2, CoCl2, and [Co(NH3)5Cl]Cl2) on the surface pressure-area isotherm of an o,o'-dihydroxyazobenzene-containing amphiphile was investigated. The isotherm of the amphiphile was little affected in the presence of CuCl2 and [Co(NH3)5Cl]Cl2, but the isotherm was greatly affected by the presence of FeCl3, FeCl2, and CoCl2, implying the formation of certain complexes at the air/water interface. In the presence of salts in the water subphase, Y-type Langmuir-Blodgett (LB) multilayers could be readily assembled on the arachidic acid precoated solid substrates. From UV/Vis and ATR-IR spectroscopy, the coordinative polymerization of the azobenzene moieties was evidenced to occur when the Fe3+, Fe2+, Cu2+, and Co2+ ions were present in the water subphase. The long axis of the azobenzene moiety seemed in all LB films to assume a nearly perpendicular orientation with respect to the solid substrate, but the orientation of the C&dbond;O bond appeared obviously different between the films prepared in the presence of FeCl3 and CuCl2. The IR spectral data indicated further that the alkyl chains in the LB film prepared in the presence of CuCl2 assumed a more close-packed structure than those prepared in the presence of FeCl3, along with an orientation 10 degrees more tilted in the former than in the latter with respect to the surface normal. Copyright 1999 Academic Press.