Infrared spectroscopic study of the molecular orientation in LB-multilayers of an amphiphilic oxadiazole

The molecular orientation present in a LB-multilayer of 2-[4-(N-dodecanoylamino) phenyl]-5-(4-nitrophenyl)-1,3,4-oxadiazole and its changes in the temperature region 22-210 8C are investigated by evaluating the polarized infrared transmission and reflection spectra, respectively, of the multilayers. Temperature-induced orientation changes of characteristic groups are qualitatively discussed in detail. For temperatures with uniaxial sample structure (22-90 8C, 210 8C) orientation angles are calculated using band intensity enhancement factors mx and mz determined for the experimental parameters chosen. At low temperatures the sample structure is stabilized by H-bridges, but above 90 8C comprehensive structural changes start and the molecules are straightening up considerably.