Solvent-Initiated Photochemistry of Transition Metal Complexes

帕特里克·霍加德博士，圣克拉拉大学化学系，由化学部无机、生物无机和有机金属计划支持，研究溶液中通过溶剂吸收光而引发的自由基链式反应。具体地说，他将确定氯仿溶剂引发的反应中的初始氧化剂是过氧基还是过氧化氢。在氯化溶剂中，我们将使用Os、钼和钯的二核和三核物种来探索金属基量子产额随照射波长的减小而增加的反应。Ru-联吡啶反应将在氧气不受限制的条件下进行探索，试图发现光可逆的、温度敏感的体系。这些现象的潜在应用包括在辐射下定期改变组成的系统，在高于给定温度的辐射下变暗的智能玻璃，以及用于破坏水中卤代烃的光催化系统。吸收光能通常被用来引发化学反应。当这些反应在氯化溶剂中进行时，对于是反应物本身吸收能量，还是溶剂分子首先吸收能量，然后将其传递给反应物，存在一些模糊的问题。这是一个重要的机械问题，因为对这些过程的清楚理解和相应的操纵能力可能导致潜在的应用。霍加德博士将研究一系列具有不同还原电位的金属络合物底物，并寻找新的溶剂引发的光反应。他还将从事氯烃在水介质中降解的光催化研究，以及对温度高度敏感的反应。这些类型的光反应可以具有高的量子产率，并可能对环境顽固的氯代烃的降解有影响。

Dr. Patrick Hoggard, Department of Chemistry, Santa Clara University, is supported by the Inorganic, Bioinorganic, and Organometallic Program of the Chemistry Division to perform studies of radical chain reactions in solution which are initiated through the absorption of light by the solvent. Specifically, he will determine whether the initial oxidizing agent in chloroform solvent-initiated reactions is a peroxy radical or a hydroperoxide. Reactions in which the metal-based quantum yield increases with decreasing irradiation wavelength will be explored using osmium, molybdenum and palladium di- and tri-nuclear species in chlorinated solvents. Ruthenium bipyridine reactions will be probed under conditions where oxygen is not limiting in an attempt to discover photoreversible, temperature-hypersensitive systems. Examples of potential applications of these phenomena include systems that periodically change composition under irradiation, `smart` glasses that darken under irradiation above a given temperature, and photocatalytic systems for the destruction of halogenated hydrocarbons in water. The absorption of light energy is commonly used to initiate chemical reactions. When these reactions take place in chlorinated solvents, there is some ambiguity as to whether the reactants themselves absorb the energy, or whether the solvent molecules absorb the energy first and then transfer it to the reactants. This is an important mechanistic question because of the potential applications which can result from a clear understanding of these processes and the corresponding ability to manipulate them. Dr. Hoggard will examine a series of metal complex substrates with differing reduction potentials and search for new solvent-initiated photoreactions. He will also pursue photocatalysis studies of chlorohydrocarbon degradation in aqueous media as well as reactions which are hypersensitive to temperature. These types of photoreactions can have high quantum yields, and may have implications for the degradation of environmentally recalcitrant chlorinated hydrocarbons.