POLARIZED SPECTROSCOPIC STUDIES OF FERROCENYL LANGMUIR-BLODGETT ASSEMBLIES

Langmuir-Blodgett (LB) assemblies of a novel electron donor, 16-ferrocenylhexadecanoic acid [eta5-(C5H5)Fe(eta5-C5H4))(CH2)15COOH], have been prepared on a solid substrate. The structures of these LB assemblies have been characterized by polarized infrared (FT-IR) spectroscopy, ellipsometry, small-angle X-ray scattering, and UV-vis spectroscopy. The polarized FT-IR experimental results show that the LB assemblies are densely packed into microcrystalline structures with a triclinic or pseudohexagonal subcell packing form. A detailed analysis of the FT-IR dichroism suggests that the axis of the all-trans hydrocarbon chains of the functionalized ferrocene fatty acid is tilted approximately 27-degrees from the surface normal and the cyclopentadienyl ring of the ferrocene chromophore in the LB assembly has a tilt angle of 53-degrees with respect to the substrate surface normal. It is also shown that these terminal ferrocene chromophores have a preferential orientation perpendicular to the film transfer direction. This is presumably due to the formation of aggregates between ferrocene chromophores in the LB assembly; aggregate formation is detectable from shifts of the UV-vis absorption in the films compared with the spectrum in solution.