Watching Photochemistry Happen: Recent Developments in Dynamic Single-Crystal X-Ray Diffraction Studies
Photoresponsive materials are an important contemporary research area with applications in, for example, energy and catalysis. Mechanistic information on solid-state photochemical reactions has traditionally come from spectroscopy and modelling, with crys
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Watching Photochemistry Happen: Recent Developments in Dynamic Single-Crystal X-Ray Diffraction Studies Lauren E. Hatcher, Mark R. Warren, Anuradha R. Pallipurath, Lucy K. Saunders, and Jonathan M. Skelton
Contents 1 Introduction 2 Linkage Isomer Systems 2.1 Nitrite (NO2) Systems 2.2 Nitrosyl (NO) Systems 2.3 Sulphur Dioxide (SO2) Systems 2.4 Dinitrogen (N2) Systems 2.5 Linkage Isomer Device Development 3 Steady-State and Pseudo-Steady-State Photocrystallographic Methodology 3.1 Experimental Setup 3.2 Static Ground and Excited States (Photostationary Structures) 3.3 Excitation Kinetics Measurements 3.4 Decay Kinetics Measurements 3.5 Pseudo-Steady-State Measurements 4 Considerations for Pump-Probe Photocrystallography 4.1 Pump-Probe Versus Pump-Multiprobe Measurements 4.2 Excitation Sources 4.3 X-Ray Sources 4.4 X-Ray Detectors 4.5 Sample Delivery
L. E. Hatcher School of Chemistry, Cardiff University, Cardiff, UK e-mail: [email protected] M. R. Warren and L. K. Saunders Diamond Light Source Ltd., Diamond House, Harwell Science and Innovation Campus, Didcot, UK A. R. Pallipurath School of Chemical and Process Engineering, University of Leeds, Leeds, UK J. M. Skelton (*) Department of Chemistry, University of Manchester, Manchester, UK e-mail: [email protected]
L. E. Hatcher et al. 4.6 Data Processing 4.7 Sub-second Linkage Isomer Studies 5 Conclusions References
Abstract Photoresponsive materials are an important contemporary research area with applications in, for example, energy and catalysis. Mechanistic information on solid-state photochemical reactions has traditionally come from spectroscopy and modelling, with crystallography limited to snapshots of endpoints and long-lived intermediates. Recent advances in X-ray sources and detectors have made it possible to follow solid-state reactions in situ with dynamic single-crystal X-ray diffraction (SCXRD) methods, allowing a full set of atomic positions to be determined over the course of the reaction. These experiments provide valuable structural information that can be used to interpret spectroscopic measurements and to inform materials design and optimisation. Solid-state linkage isomers, where small-molecule ligands such as NO, NO2, N2 and SO2 show photo-induced changes in binding to a transition metal centre, have played a leading role in the development of dynamic SCXRD methodology, since the movement of whole atoms and the predictable temperature dependence of the excited-state lifetimes make them ideal test systems. The field of “photocrystallography”, pioneered by Coppens in the late 1990s, has developed alongside advances in instrumentation and computing and can now provide the 3D structures of species with lifetimes down to femtoseconds. In this chapter, we will review the development of photocrystallography experiments against linkage isomer systems, from the early identification of metastable species under continuous illumination, through measuring kinetics at low temperature, to recent experiments studying species with sub-se
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