Molecular Orientation and Structure in LB Films of a Liquid Crystal MPUOPM Investigated by UV-Vis and IR Spectroscopy

"?Langmuir monolayers and LB films of 4-((s)-2-methylbutoxy)phenyl-(4'-(10-undecen-1-oyloxy)phenyl) methylenimine (MPUOPM) were investigated by ultraviolet-visible, polarized infrared spectroscopy. ?-A isotherms showed well-defined Langmuir monolayers were formed at an air/water interface for the MPUOPM and their mixture with SA. An inflection point at 13 mN/m appeared on the isotherm, which was due to the transition from the monolayer to multilayer. The polarized IR spectra of LB films of MPUOPM had provided new insight into the molecular orientation and structure. In LB films, the tilted angle between the alkyl chain and the normal line of the substrate was 48ffi, the tilted angle between the dipole moment of C=N and the normal line of the substrate was 51ffi. The alkyl chains assumed a trans-zigzag conformation but it included a few gauche conformers. The C=N groups were almost in one plane in the LB films. "