The original experimental data (solid points) and the QED-ET theory (diagonal stripes) have a similar trend: the ET rates increase as the energy gap increases in the Marcus inverted region, as presented in Figure . The ranges of the theoretical ET rates (upper and lower bounds of the diagonal stripes) are primarily related to the magnitudes of the transition dipole moments |μDA,D+A-|; for example, for the estrone derivatives (molecules 1 and 2), |μDA,D+A-| ranges from 0.43 to 1.07 Debye (Tables S1 and S2). Quantitatively, the discrepancies between the experiment and theory may result from nonradiative processes such as internal conversion or intersystem crossing, which is not considered in the QED-ET theory. As a result, we estimate the experimental radiative ET rates by multiplying the photoluminescence quantum yield (PLQY) with the original rates (Tables ). The PLQYs for the estrone derivatives (Figure ) and the Ru complexes (Figure and) are derived from relevant studies; for example, the PLQYs of the estrone derivatives are set as 0.5%. We emphasize that the reported non-zero PLQYs indicate the existence of QED-driven radiative ET. After this correction, the theoretical ET rates for the three molecular systems are roughly bounded by the original and corrected experimental data, indicating that the theoretical and experimental ET rates are in good agreement. The protein structure in (c) is adapted from the Protein Data Bank code 2GIW. Although the available experimental data qualitatively support the QED-ET theory, this is not sufficient to fully validate the theory due to the following problems. First, the estrone derivatives in Figure undergo intersystem crossing from the first singlet excited state (S1) to the triplet state, resulting in a low PLQY (<0.01). To identify the reason for this low PLQY, we calculated the corresponding intersystem crossing rates based on Lin's method (Table ); 55 they had a similar order of magnitude to the decay rates observed in experiments, which makes it difficult to obtain the accurate radiative ET rates. The computational methods are presented in SI Section 5. Second, the ET processes in the Ru systems (Figure and) involve multiple electronic transitions, which are beyond the scope of the QED-ET theory. Third, even with state-of-the-art theoretical methods, performing accurate computational simulations for large molecules, such as the systems in Figure and, is still non-trivial. Fourth, the nonadiabatic effects and the contributions of high-frequency modes are not involved in the QED-ET theory. The interplay between these effects and the infinite-mode QED effects on ET rates is an important issue. We believe that this issue deserves further investigations. Despite these deficiencies, the reported non-zero PLQYs support the mechanism of QED-driven radiative ET, and this comparison between theory and experiments reveals a promising avenue for investigating cavity-free QED-ET reactions. QED-induced Barrier-Free ET Reaction. QED effects may cause a barrier-free ET reaction. To demonstrate this phenomenon, we choose the Ru complexes on TiO2 thin film (the system in Figure ) as a reference system due to its reported activationless ET behaviour. In Figure , an Arrhenius plot is presented for analyzing the temperature dependence of ET rates in the QED region. The QED-ET theory demonstrates the weak temperature dependence of ET rates, showing that the activation energy Ea = 5.1 meV evaluated by the QED-ET theory is far smaller than Ea = 220 meV predicted by Marcus theory.