|M.Sc Student||Tal Marina|
|Subject||Monitoring Photochemical Reactions in Solid Inclusion|
|Department||Department of Chemistry||Supervisor||Professor Emeritus Menahem Kaftory|
|Full Thesis text|
The principal difference between solids and liquids with respect to their behavior in reactions is that the liquid phase molecules are free to adopt many conformations and different orientations with respect to each other, while in the solids they are fixed and therefore, their reactivity is structure dependent.
In many cases solid-state reactions are highly specific and may afford selectively, products that cannot otherwise be obtained. Solid-state synthesis also has the potential to become very popular because it is an environmentally favorable process.
Solid state reactions are therefore an area where crystal structure studies are essential. The basic idea behind such studies was stated ~50 years ago in the introduction to the pioneering series of investigations of solid state photochemical reactions held by Schmidt and his collaborators (Schmidt et al., 1964)
Homogeneous photochemical reactions are reactions in which the single crystallinity nature of the sample remains unchanged throughout the whole conversion range and therefore enables the determination of its crystal structure by X-ray diffraction methods in any stage of the conversion.
In inclusion compounds, the guest molecules occupy space formed by the host molecules. If the host molecules provide topochemical conditions required for bimolecular reactions and the guest molecules are photochemically active, regio- and stereo-selective reactions are anticipated.
This research was focused on finding new inclusion compounds of light sensitive guest molecules, in particular pyridone derivatives, and exploring the factors that are responsible for their undergoing a homogeneous photodimerization reaction.
It was shown that in some systems of inclusion compounds due to the dimerization of pyridone derivatives, the volume of the product decreased in respect to the reactant’s volume, and consequently, channels were formed. These channels were occupied by water molecules that penetrate the crystal from the surroundings (Lavy & Kaftory, 2007). An additional interest of this work was to find more systems in which this remarkable phenomenon might repeat.
The crystal structures of some inclusion compounds were determined. Their crystal structure and photochemical behavior were thoroughly investigated and compared with other previously investigated inclusion compounds. On the basis of comparing groups of inclusion compounds with the same guest molecules and different host molecules, the requirements that the crystal structure must provide for successful bimolecular reaction is discussed.