Experimental requirements for light-induced reactions in powders investigated by time-resolved X-ray diffraction

Abstract

A general outline of how to perform a light-excited time-resolved diffraction experiment by applying the optical pump/X-ray probe technique is given. Owing to the difference in penetration depths between the optical light (laser) pump and the X-ray probe, only specific or specially designed crystalline systems can be investigated, so special requirements have to be fulfilled concerning the sample and its compartments. A summary of the experimental conditions of optical pump/X-ray probe experiments is presented, emphasizing why the use of powder diffraction is a useful and necessary X-ray technique for this kind of experiment. The possibilities and bottlenecks of time-resolved X-ray diffraction on the picosecond time scale will be demonstrated in the powder diffraction studies of N,N-dimethylaminobenzonitrile and N,N-diisopropylaminobenzonitrile, where the photo-induced structural changes of these molecular organic systems have been studied as a function of time.

Photocrystallography

“…3. An overview of the time scales of photochemical reactions in solids has been given by Davaasambuu et al (2004).…”

Non-equilibrium dynamics of lipid bilayers

“…The second constraint is a special concern in the case of laser excitation of powder like or highly absorbing samples [45] since the absorption / extinction length of laser light and x-ray radiation dier generally by orders of magnitude. These issues will be addressed in sections A.1.1, 2.1 and A.1.2.…”

“…After this introduction, basic concepts of time resolved x-ray scattering experiments along with basic experimental and technical considerations are reviewed in chapter 2. The purpose is to provide, in combination with the literature [45,37,34,46], the information necessary to understand and set up time resolved experiments in line with the experiments performed within the context of this thesis.…”

Current developments in time-resolved X-ray diffraction

“…The (ultra)fast pump light initiates the reaction in the NIR to UV range. After this photoinitiation, a cascade of structural relaxation and reorganisation processes follows which can be probed by an x-ray pulse applying various diffraction [1][2][3][4][5][6][7][8][9][10][11][12][13] or x-ray absorption [14,15] techniques.…”

“…Systems of investigation are organic materials with optical functionalities like dyes [3,4,7,8,9,13], sensor systems, opto-electronical materials [10] or chromophores [8,9,19,20] on the one hand, and enzymes on the other hand. In the following, special interest will be given to organic materials in the solid state.…”