The Solvent Cage Effect: Using Microviscosity to Predict the Recombination Efficiency of Geminate Radicals Formed by the Photolysis of the Mo-Mo Bond of Cpʹ2Mo2(CO)6

• Main Author: Barry, Justin
• Other Authors: Pluth, Mike
• Language: en_US
• Published: University of Oregon 2018
• Subjects: Radical Polymerizations; Radical Rebound; Radicals; Solvent Cage Effect; Solvent Effects; Viscosity Effects
• Online Access: http://hdl.handle.net/1794/23713

Radicals are core reactive species that occur in almost every subfield of chemistry. In particular, solution phase radicals find their way into biochemistry (e.g. vitamin B12), and in polymer chemistry (e.g. radical polymerizations) just to name a few. Yet, given the proliferation of radical chemistry, there are still fundamental aspects of it that are poorly understood. This dissertation probed factors that influence the solvent cage effect. The solvent cage effect is where two radicals are held in close proximity to one another and prevented from easily escaping (to form free radicals) by a cage of solvent molecules. A convenient metric of the solvent cage effect is the radical recombination efficiency (FcP). Typically, FcP correlates with the bulk viscosity of the solution, however, this parameter only produces qualitative assessments. This dissertation outlines a method to quantitatively predict FcP using the microviscosity. This microviscosity dependence holds for non polar, aromatic, polar, and hydrogen-bonding solvents, along with solutions that contain polymers. Microviscosity is a great metric because it addresses an underlying reason for the solvent cage effect, the strength of the cage. Not only does the strength of the solvent cage around the radical pair affect FcP, but so does the identity of the radicals themselves. That is, the strength of the solvent cage is one piece to forming a total predictive model. FcP for the Cp'2Mo2(CO)6 dimer also varies with the wavelength of irradiation. Identifying the mechanism by which this wavelength dependence occurs may also provide another factor to include in an overall model of the solvent cage effect. Also, an attempt at synthesizing an asymmetric molybdenum dimer was performed. This asymmetric dimer would allow the study of solvent caged radical pairs that are different from each other. Predicting the photochemical cage pair recombination efficiency (FcP) is the major topic of this dissertation. However, there is also the collisional cage recombination efficiency (Fcʹ). This is where free radicals come together in what is called a collisional solvent cage pair. A method and values of Fcʹ are detailed later in this dissertation. This dissertation contains previously published and unpublished co-authored material.