MPS/CHE-EPSRC: Quantum Coherence and Correlations in Condensed Phase Photochemical Reaction Dynamics

With support from the Division of Chemistry, Professor Stephen Bradforth of the University of Southern California, along with his collaborators from the University of Bristol in the United Kingdom, is studying light-driven reactions that generate two molecules with unpaired electrons, called radical ion pairs. In some cases, the electron spin states on the two radicals can become entangled, resulting in correlated behavior even when they are well separated. Professor Bradforth and his UK collaborators are developing ultrafast spectroscopies to read out the entanglement of the molecular spin states as the products are formed, on femtosecond timescales. Their discoveries could advance our fundamental understanding of the role that quantum entanglement plays in chemical reactions. The project will also provide research opportunities for graduate and undergraduate students in advanced quantum information science and thus contribute to the creation of a quantum-enabled STEM workforce in the US. This award is made under the NSF-UKRI lead agency opportunity. Photoinduced ligand-ligand charge-transfer and photoionization reactions -- critical underlying processes in photocatalysis, protein damage and drug design -- initially form charge-transfer products composed of spin-correlated ion-radical pairs. Each ion has an unpaired electron, and the two can adopt two different spin states (singlet or triplet). In the initial stages of the chemical reaction, the two ions are generated in a spatially confined manner. Their proximity drives time-dependent spin-exchange, generating entanglement within the ion-radical pair. This key quantum property dictates parasitic reverse reactions that regenerate the parent species and therefore filter forward reaction pathways, for example by generating triplet states capable of inducing photodamage or useful long-lived charge-separation for catalysis. Multidimensional femtosecond spectroscopies, which incorporate a next generation broadband deep-ultraviolet (DUV) laser source, will be used to correlate spin with both electronic and vibrational degrees of freedom. These experiments will clarify the underlying quantum correlations between the photoprepared reactants and products, potentially revealing non-statistical spin branching occurrences that provide insight into the effects of quantum entanglement in chemical reactions. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.