Synthesis of oligofluorene modified C60 derivatives for organic solar cell applications

New oligofluorene modified C60 derivatives were designed and synthesized viarhodium complex catalyzed direct coupling between C60 and oligofluorene boronic acids in H2O/1,2-dichlorobenzene (1 : 4). The product was first purified by silica gel column chromatography and then further purified by semipreparative HPLC equipped with a Buckyprep column using toluene as an eluent. The strong deep-blue fluorescence of the oligofluorene bridge was completely quenched after end-capped with C60, indicating an efficient energy and/or charge transfer between the π-conjugated bridge and the C60 cages. Cyclic voltammetric measurements show that the HOMO and LUMO energy levels of the synthesized C60 derivatives are similar to those of widely used PC61BM. This means that the energy levels of the C60 derivatives mainly depend on the π electron system of the C60 cage. However, the substituents have huge impacts on the other physical properties of the resulting C60 derivatives, such as solubility, crystallinity, and electron mobility.