Investigating Nonadiabatic Dynamics in Phytochromes with Ultrafast Spectroscopy

Improving our understanding of nonadiabatic processes is essential for informed development of photoelectric technologies. Nonadiabatic dynamics arise due to nuclear motion on coupled potential energy surfaces. These nonadiabatic couplings are high in the regions of avoided crossings, where potential energy surfaces approach each other, and near infinity at conical intersections, where two potential energy surfaces are degenerate. Regions of high nonadiabatic coupling play an important role in the electronic dynamics of a system because of their ability to create very rapid (on the order of tens of femtoseconds) radiationless transitions between potential energy surfaces. Recent computational work has shown conical intersections to be prevalent in photochemical reactions; however, there are very few experimental investigations of conical intersections in condensed phase reactions. This is due to the extreme difficulty of detecting their subtle signatures experimentally. In biophysical chemistry, the only system that has been investigated is rhodopsin. In this photoisomerization reaction, the conical intersection produces a very rapid photoproduct formation with a quantum yield of approximately 85%. This led to the idea that the mere presence of a conical intersection in a biophysical system results in photoproducts formed with high quantum yields. In contrast, computational work shows conical intersections to be ubiquitous in all types of photoisomerization reactions. In this thesis I provide experimental evidence of conical intersections in a system with a quantum yield of