Single-Crystal to Single-Crystal Solid-State Photochemistry

Understanding the mechanism of a chemical reaction is fundamental for the understanding of chemistry. Determining the structure of reacting molecules during a reaction is a major factor in exploring the mechanism of a process. There are, however, two drawbacks in the study of the structures of the reacting species during a chemical reaction when it is carried out in solution. The first is the absence of a method for determining the structure to the level of atomic resolution, and the second is the short time a reaction may take to go to completion. The best method for structure determination is X-ray diffraction, however, the limitation is that it is being used for crystalline materials and the time for data collection is few orders of magnitude longer than the reaction time for the majority of chemical processes. In order to overcome these obstacles one is limited to the study of reactions that take place in the solid and to shorten the time of measurements. While many reactions are known to take place in the solid-state the time of measurements are still longer than is needed to follow structural changes during reaction processes. Much progress was achieved in recent years to shorten the time of data collection and I leave this subject to the experts in the field. I would like to describe examples of structurally monitoring photochemical solid-state reactions which hopefully will be reinvestigated in years to come when the goal of very fast data collection has been achieved.