Direct Investigation of Excited C₆₀ Dianion and Its Intramolecular Electron Transfer Behaviors

For the first time, the dynamics of excited fullerene dianions and associated intramolecular electron transfer (ET) were directly investigated by using femtosecond pump-probe laser flash photolysis on selectively reduced C₆₀, pyrrolidino[60]fullerene (C₆₀H), and dyads including C₆₀-naphthalenediimide (NDI) and C₆₀-pyromellitimide (PI). Upon near-infrared laser excitation, the excited dianion of C₆₀ or C₆₀H displayed two states with lifetimes of less than one and several tens of ps, attributed to prompt internal conversion from the theoretically predicted S_n state. Furthermore, the ET processes from the excited C₆₀^2- in dyad molecules, including C₆₀^2--NDI^•- and C₆₀^2--PI^•-, were confirmed with varied ET rate constants due to the difference in the driving force for ET. The current findings provide a clear description of the hitherto uncharted excited-state and photoinduced ET characteristics of fullerene dianions, paving the way for photochemical studies of excited multi-ions (excited multi-polarons) and their application in organic semiconducting materials.