Synthesis of oligofluorene modified C60 derivatives for organic solar cell applications

Abstract

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.