Capturing molecular structures during photochemical reactions of bismuth triiodide using time-resolved X-ray solution scattering

Abstract

In this dissertation, the structural changes of reaction intermediates during photoreactions were studied using time-resolved X-ray solution scattering. The target compound is bismuth triiodide (BiI$_3$), which is known to dissociate iodine radicals upon photoexcitation based on previous spectroscopic studies. In this study, through time-resolved X-ray solution scattering using a 3$^{rd}$ generation synchrotron accelerator, it was revealed that bismuth triiodide forms reaction intermediates through photoisomerization, which has not been observed before, as well as photodissociation, and the detailed structural dynamics of the reaction intermediates involved in each reaction pathway were investigated. Furthermore, by using the 4$^{th}$ generation light source, X-ray free electron laser (XFEL), which enables time-resolved X-ray solution scattering experiment with much better temporal resolution than synchrotron-based experiments, atomic movements at the onset of the reaction were traced in real time and it was found that the photoisomerization of bismuth triiodide occurs via roaming mechanism which is defined as an ultrafast intramolecular rearrangement in the van der Waals region. By synthesizing the results of the two experiments, a complete reaction scheme from the beginning to the end of the photoreaction of bismuth triiodide is presented.