The Mechanism of the Photodimerization of 60Fullerene Derivatives: It is Still a Charge Separation Followed by a Back Transfer!

摘要

Herein, we present a systematic study of the photochemical behavior of a setof fullerene compounds bearing various organic addends attached to thefullerene cage. It has been shown that the yield of photodimerization productsstrongly depends on the structure and electronic properties of the material,primarily the electron affinity (acceptor strength) of the modified fullerenecore. This finding being inconsistent with the conventional 2+2cycloadditionmechanism and pointed to an alternative pathway. This proposed pathwayinvolves photoinduced charge separation followed by back charge transferevents leading to the efficient generation of triplet excitons, which areresponsible for the formation of dimerized species. The light-induced chargeseparation pathway was confirmed by electron spin resonance spectroscopyand was supported by theoretical calculations. The revealed mechanismallows one to control the photochemical behavior of the fullerene derivativesvia rational structural engineering: some of the compounds were shown to befully resistant to photodimerization, which makes them promising candidatesin the development of stable organic photovoltaics. Furthermore, thisapproach could be used to suppress back charge transfer in donor-acceptorblends and hinder the formation of triplet excitons which represents one amajor energy loss channel in the current generation of organic solarcells.