Interplay Between Symmetry and Function in Coherent Electronic Dynamics

Abstract

In this dissertation, I tackle problems that fundamentally probe symmetry aspects of electronic dynamics in molecules and materials with functionalities in light harvesting and information processing. In Chapter 1, I briefly introduce third-order nonlinear spectroscopy to an audience initiated in the subject of physical chemistry up to the undergraduate level, with a basic understanding in quantum and statistical mechanics. I conclude the first chapter with details on the spectrometers used in answering the research problems in this dissertation. We observe, for the first time, suppression of exciton-exciton annihilation in a strongly coupled molecular H-aggregate, and we detail our findings in Chapter 2. In Chapter 3, I report the observation of chiral rate constants of exciton relaxation in a helical J-aggregate nanotube. I move on from molecular aggregates as chromophores to color centers in solid-state systems as lattice defects in Chapter 4, and use ultrafast spectroscopy to reveal the local lattice environment of nitrogen vacancy centers in diamond and explain their electronic spin dynamics observed with optically detected magnetic resonance spectroscopy. Chapter 5 takes us into the world of conical intersections, a specific topology of adiabatic potential energy surfaces in the nuclear coordinate space. We show, for the first time, that the same nuclear wave packet when launched from different points on the excited potential energy surface, can undertake drastically different trajectories despite having the same rate of relaxation through a conical intersection. These trajectories are projected on to different nuclear normal modes appearing as quantum beats in our ultrafast measurement. Lastly, I conduct a theoretical investigation to how opening a gap at a conical intersection with different topologies can influence dynamics of nuclear wave packets, and I report my findings in Chapter 6. I discuss future directions of the different projects undertaken in Chapter 7.