Study of the electrochemical and optical properties of fullerene and methano[60]fullerenediphosphonate derivatives in solution and as self-assembled structures

Four methanofullerenes with phosphonate groups attached to a C-60 core were synthesized to probe their electrochemical and optical properties both in solution and as self-assembled monolayer structures (SAMs). As the methano[60]fullerenediphosphonate is a water soluble derivative of the fullerene it has high potential as an imaging molecule in biological applications and in optoelectronics. For the processing of fullerene based SAMs different electrode substrates (ITO, Au and Si) with specific anchoring groups (zirconium, cysteamine and amino-silane) were used. The formation of the C-60-SAMs to the surfaces were investigated by atomic force microscopy (AFM), infrared spectroscopy, contact angle measurements and cyclic voltammetry. Using cyclic voltammetry it was shown that the reduction potentials of substituted methanofullerenes, both in solution and as SAMs, were slightly higher as compared with formal potentials of the redox reactions of C-60. The AFM results show that the fullerene molecules produce surface features with an apparent height of similar to 2 nm. The self-assembly strategy aims towards fabrication of electronic devices with improved interfacial contact, a prerequisite in order to obtain enhanced electron transfer between acceptor-donor materials.