CMOS
Complementary metal-oxide-semiconductor
dcpe
1,2-Bis(dicyclohexylphosphino)ethane
dppe
1,2-Bis(diphenylphosphino)ethane
ES
Excited state
Et 4 dien
N,N,N
0 ,N
0 -Tetraethyldiethylenetriamine
GS
Ground state
JMAK
Johnson-Mehl-Avrami-Kolmogorov
LED
Light-emitting diode
MS 1
Metastable state 1
MS 2
Metastable state 2
MX
Macromolecular crystallography
OTf
Trifluoromethanesulfonate
SCXRD Single-crystal X-ray diffraction
SFX
Serial femtosecond crystallography
SNP
Sodium nitroprusside
TR
Time resolved
XFEL
X-ray free-electron laser
1 Introduction
Modern time-resolved (TR) spectroscopy with pulsed lasers can routinely access
nanosecond and femtosecond timescales. However, unless spectroscopic signatures
can be assigned to transient species, for example, using theoretical modelling,
interpreting the data from these studies can be challenging. Recent advances in
X-ray sources and detectors make possible an alternative: time-resolved singlecrystal X-ray diffraction (TR-SCXRD) [1]. A TR-SCXRD experiment yields a
sequence of snapshots of the full 3D structure of the crystal over the course of a
solid-state reaction. This allows for transient species or intermediates to be identified
to a high level of confidence without a priori knowledge, provided they are present at
more than a few % of the crystal volume. State-of-the-art serial crystallography
measurements pioneered by the macromolecular crystallography (MX) community
using X-ray free-electron laser (XFEL) sources can access femtosecond dynamics,
while experiments using synchrotron and laboratory X-ray light sources can be used
to study species with lifetimes from picoseconds to seconds and longer, allowing a
wide range of light-activated solid-state reactions to be visualised in 3D.
While TR-SCXRD methods were pioneered by the MX community [2], the
earliest in situ dynamic SCXRD studies on molecular crystals were performed in
the 1990s to investigate the unexpectedly long-lived metastable excited states in
transition metal linkage isomers [1], which have since served as model systems for
more recent developments.
Linkage isomerism is a phenomenon where a ligand can display two or more
distinct binding modes to a transition metal centre. The first reports of linkage
Watching Photochemistry Happen: Recent Developments in Dynamic Single-Crystal. . .
201
Complementary metal-oxide-semiconductor
dcpe
1,2-Bis(dicyclohexylphosphino)ethane
dppe
1,2-Bis(diphenylphosphino)ethane
ES
Excited state
Et 4 dien
N,N,N
0 ,N
0 -Tetraethyldiethylenetriamine
GS
Ground state
JMAK
Johnson-Mehl-Avrami-Kolmogorov
LED
Light-emitting diode
MS 1
Metastable state 1
MS 2
Metastable state 2
MX
Macromolecular crystallography
OTf
Trifluoromethanesulfonate
SCXRD Single-crystal X-ray diffraction
SFX
Serial femtosecond crystallography
SNP
Sodium nitroprusside
TR
Time resolved
XFEL
X-ray free-electron laser
1 Introduction
Modern time-resolved (TR) spectroscopy with pulsed lasers can routinely access
nanosecond and femtosecond timescales. However, unless spectroscopic signatures
can be assigned to transient species, for example, using theoretical modelling,
interpreting the data from these studies can be challenging. Recent advances in
X-ray sources and detectors make possible an alternative: time-resolved singlecrystal X-ray diffraction (TR-SCXRD) [1]. A TR-SCXRD experiment yields a
sequence of snapshots of the full 3D structure of the crystal over the course of a
solid-state reaction. This allows for transient species or intermediates to be identified
to a high level of confidence without a priori knowledge, provided they are present at
more than a few % of the crystal volume. State-of-the-art serial crystallography
measurements pioneered by the macromolecular crystallography (MX) community
using X-ray free-electron laser (XFEL) sources can access femtosecond dynamics,
while experiments using synchrotron and laboratory X-ray light sources can be used
to study species with lifetimes from picoseconds to seconds and longer, allowing a
wide range of light-activated solid-state reactions to be visualised in 3D.
While TR-SCXRD methods were pioneered by the MX community [2], the
earliest in situ dynamic SCXRD studies on molecular crystals were performed in
the 1990s to investigate the unexpectedly long-lived metastable excited states in
transition metal linkage isomers [1], which have since served as model systems for
more recent developments.
Linkage isomerism is a phenomenon where a ligand can display two or more
distinct binding modes to a transition metal centre. The first reports of linkage
Watching Photochemistry Happen: Recent Developments in Dynamic Single-Crystal. . .
201