Synthesis and characterization of amphiphilic fullerenes and their Langmuir-Blodgett films

We report here the synthesis and characterization of three amphiphilic fullerene derivatives and their Langmuir-Blodgett thin films. Two of the C-60 amphiphiles are mono-derivatives with a long alkyl chain terminated with either -COOH (2) or NH2 (3) as the hydrophilic headgroup, and the third one (5) is designed to bear the same NH2 group as 3 but with 10 additional hydrophobic alkyl chains grafted on the C-60 sphere (Scheme 1). These amphiphiles form stable, ordered monolayers at the air-water interface. The molecular packing at the air-water interface and the mean area per molecule are determined by pressure isotherms at room temperature. Hysteresis of pressure isotherms of side chain C-60 (5) shows complete reversibility upon compression and decompression, which suggests that side chains on the C-60 sphere inhibit formation of aggregates at the air-water interface. Comparative studies of all three amphiphiles allow us to better determine the interaction between C-60's and their self-assembly kinetics at the air-water interface. Monolayers of monoderivatized amphiphiles (2 and 3) were transferred successfully onto quartz substrates as Z-type multilayered Langmuir-Blodgett films, and monolayers of 5 were transferred as Y-type films. Detailed characterization of the multilayer films (Z-type deposition) prepared from amine-terminated C-60 (3) using X-ray and neutron reflectometry reveals staggering Of C-60 spheres and a head-to-head (Y-type) structure presumably due to flipping and reattaching of C-60 amphiphiles to the previous underlying C-60 layer.