Photoinduced Structural Changes as the Factor Influencing the Direction of the Photochemical Reaction in the Crystal

The path of the Norrish–Yang reaction of methylammonium 4-(2,4,6-triisopropylbenzoyl)benzoate was studied by means of X-ray structure analysis. The following parameters influenced by this photochemical reaction were monitored: (a) intramolecular distances and angles in the reaction center, (b) the size of the free space near the reactive atoms, (c) the mutual orientation of molecular fragments, (d) the cell parameters, and (e) the product content. Product molecules were created in two modes, namely, by the reaction of the 2-isopropyl or 6-isopropyl group, which has not been revealed previously for other 2,4,6-triisopropylbenzophenones. The 2-isopropyl group took part in the photochemical reaction during the whole crystal transformation, whereas the reaction of the 6-isopropyl group started with a delay and ceased before the total crystal conversion. The reason for such behavior was explained by the analysis of changes in the free space near both o -isopropyl groups with the crystal phototransformation.