This grant in Organic and Macromolecular Chemistry provides support for the research of Dr. Charles Doubleday, Columbia University. The work is focused on understanding the behavior of species generated during photochemical reactions, an understanding of which is essential for solar energy conversion. In many organic reactions, discrete, highly energetic, intermediate molecules are formed which then are transformed to final products. Biradicals are an example of reactive intermediates which are highly energetic molecules formed in a variety of reactions. The ultimate fate of such reactions, the identity of the products and their rates of formation, depends on the properties of the biradical intermediates. To understand reactions proceeding via biradicals, one must understand the properties of the biradicals. Their short lifetimes make this a challenging task. Both an experimental and theoretical study of biradicals will be carried out. The experiments involve nanosecond transient UV absorption in both the gas and condensed phase. Measurement of biradical lifetimes in the gas phase will supply the biradical dynamics in the absence of solvent interactions. Two sets of calculations will be applied to biradicals. One will focus on the role of entropy in controlling the dynamics of biradicals in the singlet electronic spin state. The other will examine singlet-triplet crossings by calculating the singlet-triplet energy separations and spin-orbit couplings in biradicals and radical pairs.
