4.6 Data Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 232
4.7 Sub-second Linkage Isomer Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234
5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
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, NO 2
À , N 2
and SO 2 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-second lifetimes. We will
discuss the advances in X-ray sources and instrumentation that have made dynamic
SCXRD experiments possible, and we will highlight the role of kinetic modelling
and complementary spectroscopy in designing experiments. Finally, we will discuss
possible directions for future development and identify some of the outstanding
challenges that remain to be addressed.
Keywords Lasers · LEDs · Linkage isomers · Metastable states · Photochemistry ·
Photocrystallography · Reaction kinetics · Solid state · X-ray diffraction
Abbreviations
2D
Two-dimensional
3D
Three-dimensional
bipy
2,2
0 -Bipyridine
BPh 4
Tetraphenylborate
Bu 4 dien
N,N,N
0 ,N
0 -Tetrabutyldiethylenetriamine
CCD
Charge-coupled device
200
L. E. Hatcher et al.
4.7 Sub-second Linkage Isomer Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234
5 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 234
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 235
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, NO 2
À , N 2
and SO 2 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-second lifetimes. We will
discuss the advances in X-ray sources and instrumentation that have made dynamic
SCXRD experiments possible, and we will highlight the role of kinetic modelling
and complementary spectroscopy in designing experiments. Finally, we will discuss
possible directions for future development and identify some of the outstanding
challenges that remain to be addressed.
Keywords Lasers · LEDs · Linkage isomers · Metastable states · Photochemistry ·
Photocrystallography · Reaction kinetics · Solid state · X-ray diffraction
Abbreviations
2D
Two-dimensional
3D
Three-dimensional
bipy
2,2
0 -Bipyridine
BPh 4
Tetraphenylborate
Bu 4 dien
N,N,N
0 ,N
0 -Tetrabutyldiethylenetriamine
CCD
Charge-coupled device
200
L. E. Hatcher et al.