Perfluorocubane as a σ* orbital-based electron acceptor beyond classical electron-transfer models.

Perfluorocubane is an unconventional electron acceptor whose lowest unoccupied molecular orbital is composed entirely of σ* orbitals. In contrast to conventional acceptors that stabilize excess charge through π*-orbital delocalization, perfluorocubane confines an electron with its compact cubic scaffold, giving rise to an almost point-charge-like electronic structure. Such an electronic configuration is expected to produce electron-transfer (ET) behavior beyond established donor-acceptor models. Here we investigate intramolecular photoinduced ET in a donor-acceptor molecule combining dimethylfluorene and perfluorocubane. Picosecond time-resolved transient absorption spectroscopy directly reveals charge separation and recombination in polar solvents. Analysis of the ET kinetics within the semiclassical Marcus framework yields an unusually large electronic coupling together with a substantial reorganization energy, an uncommon combination in π-conjugated donor-acceptor systems. These distinctive ET characteristics are attributed to the σ*-derived LUMO and the compact cubic architecture of perfluorocubane, establishing this molecule as a platform for accessing previously unexplored regimes of molecular electron-transfer chemistry.