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1.  Ultrafast spin-state photoswitching in a crystal and slower consecutive processes investigated by femtosecond optical spectroscopy and picosecond X-ray diffraction 
We report the spin state photo-switching dynamics in two polymorphs of a spin-crossover molecular complex triggered by a femtosecond laser flash, as determined by combining femtosecond optical pump-probe spectroscopy and picosecond X-ray diffraction techniques,. The light-driven transformations in the two polymorphs are compared. Combining both techniques and tracking how the X-ray data correlate with optical signals allows understanding of how electronic and structural degrees of freedom couple and play their role when the switchable molecules interact in the active crystalline medium. The study sheds light on crossing the border between femtochemistry at the molecular scale and femtoswitching at the material scale
doi:10.1039/c2cp23587k
PMCID: PMC3463002  PMID: 22294040
2.  Restricted Photochemistry in the Molecular Solid State: Structural changes on Photoexcitation of Cu(I) Phenanthroline metal-to-ligand-charge-transfer (MLCT) complexes by Time-Resolved Diffraction 
The journal of physical chemistry. A  2012;116(13):3359-3365.
The excited state structure of [Cu(1)[(1,10-phenanthroline-N,N’) bis(triphenylphosphine)] cations in their crystalline [BF4] salt has been determined at both 180 and 90K by single-pulse time-resolved synchrotron experiments with the modified polychromatic Laue method. The two independent molecules in the crystal show distortions on MLCT excitation which differ in magnitude and direction, a difference attributed to a pronounced difference in the molecular environment of the two complexes. As the excited states differ, the decay of the emission is bi-exponential with two strongly different lifetimes, the longer lifetime, assigned to the more restricted molecule, becoming more prevalent as the temperature increases. Standard deviations in the current Laue study are very much lower than those achieved in a previous monochromatic study of a Cu(I) 2,9 dimethyl-phenanthroline substituted complex (J. Am. Chem. Soc. 2009, 131, 6566), but the magnitude of the shifts on excitation is similar, indicating that lattice restrictions dominate over the steric effect of the methyl substitution. Above all the study illustrates emphatically that molecules in solids have physical properties different from those of isolated molecules and that their properties depend on the specific molecular environment. This conclusion is relevant for the understanding of the properties of molecular solid state devices which are increasingly used in current technology.
doi:10.1021/jp300313s
PMCID: PMC3545449  PMID: 22385365
3.  The development of Laue techniques for single-pulse diffraction of chemical complexes: time-resolved Laue diffraction on a binuclear rhodium metal-organic complex 
A modified Laue technique suitable for time-resolved diffraction is described in which profile-independent integration is used, the RATIO method is applied and multi-crystal data are normalized to a common scale. The method is applied in single-pulse pump–probe studies of a binuclear Rh complex, showing Rh—Rh bond shortening of 0.136 (8) Å on excitation.
A modified Laue method is shown to produce excited-state structures at atomic resolution of a quality competitive with those from monochromatic experiments. The much faster data collection allows the use of only one or a few X-ray pulses per data frame, which minimizes crystal damage caused by laser exposure of the samples and optimizes the attainable time resolution. The method has been applied to crystals of the α-modification of Rh2(μ-PNP)2(PNP)2 (BPh4)2 [PNP = CH3N(P(OCH3)2)2, Ph = phenyl]. The experimental results show a shortening of the Rh—Rh distance in the organometallic complex of 0.136 (8) Å on excitation and are quantitatively supported by quantum-mechanical (QM)/molecular-mechanics (MM) theoretical calculations which take into account the confining effect of the crystal environment, but not by theoretical results on the isolated complex, demonstrating the defining effect of the crystal matrix.
doi:10.1107/S0108767311011883
PMCID: PMC3121236  PMID: 21694470
Laue techniques; single-pulse diffraction; quantum-mechanical/molecular-mechanics calculations; QM/MM calculations; time-resolved X-ray crystallography
4.  Time-resolved Laue diffraction of excited species at atomic resolution: 100 ps single-pulse diffraction of the excited state of the organometallic complex Rh2(μ-PNP)2(PNP)2 ·BPh4 
The polychromatic Laue technique has been applied in 100 ps delay synchrotron pump–probe experiments of the triplet excited state of a Rh(I) dinuclear complex. The observed contraction of the Rh–Rh distance of 0.154 (13) Å is less than predicted by a series of theoretical calculations, a difference attributed to the constraining effect of the crystal lattice.
doi:10.1039/c0cc04997b
PMCID: PMC3129623  PMID: 21210070

Results 1-4 (4)