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

An amphiphilic C-60 molecule with a substituent having a hydrophilic c arboxylic group at the end was found to form a monolayer at the air-wa ter interface and the structure of the Langmuir-Blodgett (LB) film (Z- type) was elucidated. The shortest distance between the C-60 was estim ated 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 moiet y in two dimensions. Adjacent C-60 moieties have an electronic interac tion which was shown in the red-shift of the characteristic bands in t he UV/vis absorption spectrum of the LB film compared with that of a s olution spectrum. Several lines of evidence suggested that the molecul e has an oblique orientation in the LB film and exists in a pairwise m anner due to the dimer formation of the carboxylic groups within a mon olayer, not between the adjacent monolayers. The AFM observations reve aled that the surface of a single-layer LB film, which consists of dom ains of ca. 0.1 mu m in diameter, is rather smooth and that the undula tion is +/-1 nm for most of the surface except for defects such as vac ancy and bilayer regions. The area fractions of the monolayer, the vac ancy, 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.