Sensitization of fullerenes by covalent attachment of a diketopyrrolopyrrole chromophore

In an effort to develop new materials for organic solar cell applications, we have synthesized triads of 3,6-dithien-2-yl-2,5-dialkylpyrrolo[3,4-c]pyrrole-1,4-dione (DTDPP) covalently linked at the nitrogen positions to two [6,6]-phenyl-C61-butyric acid ester (PCB) units via alkyl chains of different lengths. We present here the excited-state properties of the compounds in solution, as investigated by (time-resolved) spectroscopy. The absorption spectra of the triads are the composite of the ones recorded with the separate fullerene and DTDPP parent molecules, indicating weak electronic coupling between the sub-units. However, the fluorescence quantum yield drops from 74% in pure DTDPP to