LANGMUIR-BLODGETT-FILM OF AMPHIPHILIC C-60 CARBOXYLIC-ACID

An amphiphilic C-60 molecule with a substituent having a hydrophilic carboxylic group at the end was found to form a monolayer at the air-water interface and the structure of the Langmuir-Blodgett (LB) film (Z-type) was elucidated. The shortest distance between the C-60 was estimated to be 0.95 nm using a limiting area per molecule of 0.78 nm(2) at the air-water interface, assuming the close packing of the C-60 moiety in two dimensions. Adjacent C-60 moieties have an electronic interaction which was shown in the red-shift of the characteristic bands in the UV/vis absorption spectrum of the LB film compared with that of a solution spectrum. Several lines of evidence suggested that the molecule has an oblique orientation in the LB film and exists in a pairwise manner due to the dimer formation of the carboxylic groups within a monolayer, not between the adjacent monolayers. The AFM observations revealed that the surface of a single-layer LB film, which consists of domains of ca. 0.1 mu m in diameter, is rather smooth and that the undulation is +/-1 nm for most of the surface except for defects such as vacancy and bilayer regions. The area fractions of the monolayer, the vacancy, and the bilayer regions were estimated to be 88 +/- 7, 7 +/- 5, 5 +/- 3%, respectively. The layer structure was also confirmed using X-ray diffraction analyses which indicate the repeat distance of ca. 2.6 nm along the surface normal of the multilayer LB film.