We describe a metal-free, photocatalytic hydrodefluorination (HDF) of polyfluoroarenes (FA) using pyrene-based photocatalysts (Py). The weak "pi-Hole-pi" interaction between Py and FA promotes the electron transfer against unfavorable energetics (Delta G(ET) up to 0.63 eV) and initiates the subsequent HDF. The steric hindrance of Py and FA largely dictates the HDF reaction rate, pointing to an inner-sphere electron transfer pathway. This work highlights the importance of the size and shape of the photocatalyst and the substrate in controlling the electron transfer mechanism and rates as well as the overall photo catalytic processes.