Photochemical Transformation of Fullerenes

Experimental findings and associated theoretical insights regarding the photochemical transformation of fullerenes are reported, which challenge the conventional wisdom in the field and point out a viable path towards improved fullerene-based electronic devices. It is shown that the efficiency of the photochemical monomer-to-dimer transformation of the fullerene [6,6]-phenyl-C-61-butyric acid methyl ester (PCBM) is strongly dependent on the light intensity, and this is utilized to demonstrate that direct patterning of an electroactive PCBM film can be effectuated by sub-second UV-light exposure followed by development in a tuned developer solution. By straightforward analytical reasoning, it is demonstrated that the observed intensity-dependent monomer-to-dimer transformation dictates that a significant back-reaction to the ground state must be in effect, which presumably originates from the excited-triplet state. By a combination of numerical modeling and analytical argumentation, it is further shown that the final dimer formation must constitute a bi-excited reaction between two neighboring monomers photo-excited to the triplet state.