PhD defense - Ratkovec (Reid/Rumbles group)

About this event

Title: Electron Spin Polarization through Upside-Down Charge Transfer

Abstract:

While classical photoinduced electron transfer (PET) excites neutral molecules to generate charged ions, this work explores a powerful thermodynamic alternative: photoinduced charge neutralization (PCN). By exciting pre-associated, ground-state ion pairs, PCN generates an “upside-down" charge transfer state composed of highly energetic neutral molecules. This inverse pathway rigorously eliminates diffusion-controlled rate limits and allows the resulting neutral species to separate efficiently, storing captured photon energy for downstream chemical transformations.

Building upon this foundation, this work investigates how low-dielectric media favorably alters reaction thermodynamics. Rigorously factoring in classical electrostatic corrections reveals that non-polar environments can fundamentally invert reaction spontaneity. This energetic inversion transforms the photooxidation of routinely assumed "inert" counterions into a predictable, thermodynamically favorable tool for driving previously inaccessible chemistry.

Beyond thermodynamics, we demonstrate that the intense electrostatic confinement inherent to these ionically paired molecules directs unique spin dynamics. By studying stable, ground-state contact radical ion pairs, we show that optical excitation drives non-equilibrium spin populations, generating long-lived electron spin polarization at cryogenic temperatures. Furthermore, targeted synthetic extensions of the acceptor molecule serve as a precise spatial ruler. This structural control allows for the predictable attenuation of both exchange and dipolar couplings, establishing a novel molecular framework designed to optically pump electron spin polarization.