Abstract
The influence of external stimuli on the decrease of crystal diffracting power and hence the quality of diffraction patterns and determined structures was studied in the case of the Norrish-Yang photochemical reaction of methyl 2-{[4-(2,4,6-triisopropylbenzoyl)benzoyl]amino}-3-phenylpropanoate, compound 1. The reaction was conducted in a single-crystal-to-single-crystal homogeneous manner. The calculated rate constant at 75 °C was 1.6 × 10−3 s−1. In a quantitative way we illustrated a relationship between the reduction of the crystal diffracting power and the content of reactant molecules in the crystal and quantitatively showed that reactant molecules are responsible for this reduction. We observed that there is no correlation between the energy of UV–vis radiation applied to induce the photochemical reaction and the degree of the decrease of crystal diffracting power. We also showed in the case of the studied crystals that some change in temperature does not influence the degree of the decrease of the crystal diffracting power under the influence of UV–vis radiation. The unknown structures of the crystals containing pure reactant and product for compound 1 were also presented. The influence of different external stimuli on the reduction of diffracting power of crystals was monitored quantitatively during and after the Norrish-Yang photochemical reaction.
Highlights
The influence of external stimuli on the decrease of crystal diffracting power and the quality of diffraction patterns and determined structures was studied in the case of the Norrish-Yang photochemical reaction of methyl 2-{[4-(2,4,6-triisopropylbenzoyl)benzoyl]amino}-3-phenylpropanoate, compound 1
When photochemical reactions in single crystals and structural transformations brought about by such reactions are monitored by X-ray diffraction, it is crucial to have crystal structures of high quality which depends on the quality and intensity of reflections collected for crystals
On the grounds of the results described in the present paper, some advice on how to conduct photochemical reactions in crystals monitored by X-ray diffraction will be given
Summary
When photochemical reactions in single crystals and structural transformations brought about by such reactions are monitored by X-ray diffraction, it is crucial to have crystal structures of high quality which depends on the quality and intensity of reflections collected for crystals. When we analyzed our X-ray data and data available in scientific literature, we noticed that for many compounds the common feature is a certain decrease of a number of observed reflections, i.e. reflections of intensity I [ 2r(I), with time of irradiation of crystals by a UV–vis beam and with the progress of a photochemical reaction. Such a decrease indicates that crystal diffracting power and translational order decreases along with the progress. It should be emphasized that the crystals did not change their external appearance, i.e. transparency, color, shape and size and they did not crack during irradiation
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