Monitoring Structural Transformations in Crystals. Part 15. Structural Changes in Crystals Caused by UV Radiation Despite the Lack of a Photochemical Reaction

Abstract

Crystals of 3-benzoylbicyclo[2.2.1]heptane-2-carboxylic acid (C 15 H 16 O 3 ) do not undergo the photochemical reaction, namely the Yang photocyclization, but they undergo UV radiation damage. The initial stages of this process were monitored by X-ray diffraction and structure analysis. The results show that the process is smooth and accompanied by the decrease of the overall scale factor, the certain increase of width of reflections, the increase of the cell parameters, intermolecular distances, atomic displacement parameters and the small changes in orientation of molecular fragments.

Monitoring Photochemical Reactions in Single Crystals by X-ray Diffraction: Practical Aspects

“…Hydrogen atoms were omitted for clarity of the photochemical reaction (connected with the time of UV-vis irradiation and the content of product molecules in a crystal). This illustration can be compared with the crystal behavior observed by us for two other compounds, which did not give the product of a photochemical reaction [1,3]. In their cases, the decrease of crystal diffracting power was observed during the whole UV-vis irradiation process until the total loss of reflections.…”

“…To the best of our knowledge, there are only three papers in which relationships between the decrease of crystal diffracting power and crystal structures were analyzed [1][2][3], but each of the compounds presented in these papers were studied for only one set of external conditions. In the research presented in this paper, we induced a photochemical reaction in crystals of one compound applying different conditions of photochemical induction, namely, various energies of a UV-vis beam and various temperatures.…”