Dr. Shahnawaz Rather, The University of Kentucky

Title: From Coherence to Correlation: Electron-Nuclear Dynamics in Photoinduced Processes

Abstract: Researchers have long pondered whether quantum mechanics might be relevant to the functioning of chemical and biological systems. This idea has fascinated scientists and the public alike, yet it has proven difficult to move beyond speculation and address the central question of functionally relevant quantum effects unequivocally. The challenge has been that realistic chemical or biological systems exhibit enormous energetic disorder, preventing quantum coherence effects from surviving over functionally relevant timescales. However, recent work has indicated that coherence phenomena can appear differently from what researchers initially expected. Rather than manifesting or functioning as quantum bits, coherence effects in molecular systems appear to involve electron-nuclear correlations that can be robust and functionally relevant.

I will present the state of recent discoveries that extend beyond the extensively studied photosynthetic systems. I argue that electron transfer reactions occurring on ultrafast timescales provide a profound basis for understanding electron–nuclear correlations and demonstrate how vibrations can dictate reaction outcomes. I will discuss electron-nuclear correlations through the spin-vibronic effect and how it regulates singlet–triplet conversion in binuclear transition-metal complexes. I will also describe how electron-nuclear interactions can drive energy flow in photocatalysts from a light-harvesting site to a reaction site by bridging the two entities via vibronic delocalization. Toward the end, I will share some of our recent results on shifting vibronic resonances in singlet fission. I will conclude with a forecast that order on the quantum-mechanical scale, even in energetically disordered systems, can emerge from robust electron-nuclear correlations. This understanding could ultimately enable the design of structural control elements for enhanced functioning of energy-conversion systems.