The importance of knowing the structure of a material to atomic resolution, the number and nature of the connectivities between the atoms, is fundamental in understanding the properties of the material. X-ray crystallography is the best method of obtaining the detailed structure of solid materials, and provides a 3D picture of the structure. However, until now, it is a technique that only looks as molecules in their ground (unreactive) state. In this proposal, for the first time, we wish to introduce the dimension of time into the crystallographic experiment. By combining the X-ray experiment with a synchronised light source, that activates the molecules into an excited (reactive) state, we will look at the structures of species with lifetimes of microseconds or even nanoseconds. To achieve this we need to build protective molecular cages around these photoreactive molecules, and to compare their solid state behaviour with what occurs in solution using time resolved IR techniques.