Maciej Krzeszewski, Eli M. Espinoza, Ctirad Červinka, James B. Derr, John A. Clark, Dan Borchardt, Gregory J. O. Beran, Daniel T. Gryko, Valentine I. Vullev

Electric dipoles are everywhere, and the importance of understanding how they affect chemical, physical and biological processes cannot be overstated. Electron transfer (ET) is essential for sustaining life and for making energy conversion possible. Molecular dipoles present important, but underutilized, paradigms for guiding ET processes. While dipoles generate fields of Gigavolts per meter in their vicinity, reported differences between rates of ET along vs. against dipoles are often small or undetectable. Here we show unprecedentedly large dipole effects on ET. Depending on their orientation, dipoles either ensure picosecond ET, or turn ET completely off. Furthermore, favourable dipole orientation makes ET possible even in lipophilic medium, which appears counterintuitive for non-charged donor-acceptor systems. Our analysis reveals that dipoles can substantially alter the ET driving force for low solvent polarity, which accounts for these unique trends. This discovery opens doors for guiding forward ET processes, while suppressing undesired backward electron transduction, which is one of the holy grails of photophysics and energy science.