Zeitschrift für Kristallographie - Crystalline Materials

Published by De Gruyter (O)

Volume 223 Issue 4-5 - Photocrystallography

Issue of Zeitschrift für Kristallographie - Crystalline Materials

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Contents
Journal Overview

September 25, 2009

Preface: Photocrystallography

Page range: IV-IV

September 25, 2009

Out-of-equilibrium charge density distribution of spin crossover complexes from steady-state photocrystallographic measurements: experimental methodology and results

Sébastien Pillet, Vincent Legrand, Hans-Peter Weber, Mohamed Souhassou, Jean-François Létard, Philippe Guionneau, Claude Lecomte

Page range: 235-249

Abstract

The electron density distribution of a light-induced molecular excited state, i.e. the high spin metastable state of [Fe(phen) 2 (NCS) 2 ], was determined from steady-state photocrystallographic measurements. We defined the experimental conditions under which the accuracy of the measured diffraction data is compatible with an electron density analysis. These include: (i) a large structural and electronic contrast between high spin (HS) and low spin (LS) states, (ii) an efficient photoconversion under light irradiation and (iii) slow relaxation of the HS metastable state. Multipolar modeling of the electron density yielded a deformation density and 3 d -orbital populations for Fe(II) characteristic of a high spin ( t 2g 4 e g 2 ) electron configuration and support the assumption of significant σ-donation and π-backbonding of the Fe—N interactions. The electron density distribution in the intermolecular regions confirms anisotropic intermolecular interactions with possibly a layer topology parallel to the orthorhombic ( ab ) plane, related to the system cooperativity.

September 25, 2009

Light-induced phase separation (LIPS) into like-spin phases observed by Laue neutron diffraction on a single crystal of [Fe(ptz)₆](BF₄)₂

François Varret, Kamel Boukheddaden, Antoine Goujon, Béatrice Gillon, Garry J. McIntyre

Page range: 250-258

Abstract

We have followed the photo-transformation, the light-induced thermal hysteresis, and the light-induced phase separation (LIPS) into like-spin phases on a [Fe(ptz) 6 ](BF 4 ) 2 single crystal, in the quenched rhombohedral phase, through the analysis of neutron Laue diffraction patterns. In agreement with the analysis of previous magnetic measurements, phase separation was observed in the close vicinity of the static light-induced instability, but not otherwise. The positions of the Laue spots were analysed in terms of variation in the a / c lattice-parameter ratio which is well correlated with the variation of the high-spin fraction predicted by a simple homogeneous mean-field model. Using a mapped version of the same model, we analyzed the line shapes of the Laue spots during photo-excitation and relaxation experiments so as to determine the width of the distribution of irradiation intensities, a crucial parameter in phase separation. The predictions of the mapped model failed to reproduce the rapid initial kinetics of the phase separation process, but were in agreement with the further evolution. These features are attributed to a nucleation and growth process, for which the crossover from microscopic to macroscopic regimes has been observed.

September 25, 2009

Neutron photocrystallography: simulation and experiment

Jürg Schefer, Dominik Schaniel, Václav Petříček, Theo Woike

Page range: 259-264

Abstract

The investigation of light-induced structural changes by diffractive methods has improved significantly in the last two decades. We present here the case of neutron photocrystallography for which we have built a special experimental setup at the single crystal neutron diffractometer TriCS at the Swiss Spallation Neutron Source SINQ. We illustrate the progress of the method on the example of the structural determination of photoinduced nitrosyl linkage-isomers in Na 2 [Fe(CN) 5 NO] · 2 H 2 O. The in-situ determination of the population of the light-induced linkage isomers by optical transmission measurements enhances the reliability of such structural investigations considerably. Additionally we present a new simulation tool within the program package JANA2006 which allows to plan a photocrystallographic experiment thoroughly since the required q -range, the minimally needed population of the photoinduced species, as well as the necessary counting statistics for a successful single crystal diffraction experiment can be evaluated in advance.

September 25, 2009

Static and time-resolved photocrystallographic studies in supramolecular solids

Philip Coppens, Shao-Liang Zheng, Milan Gembicky

Page range: 265-271

Abstract

The supramolecular solid state is a medium par excellence for photochemical studies of molecules in a well-defined environment. If the photoactive molecule is embedded within a strong photochemically-inert framework, reactions can proceed without breakdown of the crystal lattice. A number of examples of trans-cis and cis-trans reactions are presented. A variable temperature study of Zn-coordinated tiglic acid shows that the reaction is energy-controlled with a small activation energy of approx. 2 kJ/mol, dependent on the size of the cavity in which the molecule is located. Time-resolved studies of the instantaneous dimer-formation of an organic and an inorganic species are presented. The Cu(I)(NH 3 ) 2 cation forms a dimeric species with a contracted Cu(I)—Cu(I) distance through promotion of an electron from an antibonding to a weakly bonding orbital, whereas xanthone forms an excimer with decrease interplanar spacing. The concept of the photodifference map is defined and used thoughout the article.

Open Access September 25, 2009

State of the art and opportunities in probing photoinduced phase transitions in molecular materials by conventional and picosecond X-ray diffraction

Eric Collet, Marylise Buron-Le Cointe, Maciej Lorenc, Hervé Cailleau

Page range: 272-282

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Abstract

The optical control of the macroscopic physical properties (magnetic, optical …) of a material by laser irradiation is gaining interest through the emerging field of photoinduced phase transitions. Light-induced changes of the macroscopic state of a material involves subtle coupling between the electronic and structural degrees of freedom, which are essential to stabilize the photo-excited state, different in nature from the stable state. Therefore the new experimental field of photocrystallography plays a key role. It goes far beyond simple structural analysis under laser excitation. By playing on different physical parameters and developing the techniques and analysis, one can investigate new out of equilibrium physics through light-driven cooperative dynamics and transformations in materials. This paper is reviewing different aspects of the use of photocrystallography to investigate the nature, the mechanisms and the dynamics of photoinduced phase transitions for photo-steady or long-lived states, as well as transformations driven by an ultra-short light pulse. We also give a brief overview on recent advances in time-resolved crystallography with 100 ps resolution.

September 25, 2009

Real-time studies of reversible lattice dynamics by femtosecond X-ray diffraction

Clemens v. Korff Schmising, Matias Bargheer, Michael Woerner, Thomas Elsaesser

Page range: 283-291

Abstract

Ultrafast X-ray diffraction allows for observing structural dynamics of condensed matter in real-time, in this way directly probing reversible and irreversible geometry changes on atomic length and time scales. This article reports recent progress in this rapidly developing field, focusing on experimental work performed with laser-driven X-ray sources. After an introduction into the state-of-the-art methods for generation and measurement, we discuss coherent lattice motions of ferroelectric nanolayered systems and structural dynamics related to polar dipole solvation in bulk molecular crystals.

September 25, 2009

Towards pump-probe resonant X-ray diffraction at femtosecond undulator sources

Gerhard Ingold, Rafael Abela, Paul Beaud, Steven Lee Johnson, Urs Staub

Page range: 292-306

Abstract

The first tunable undulator source for femtosecond hard X-rays in the range 4–12 keV is now in operation at the SLS storage ring. The source combines accelerator and laser technology relevant for future seeded free electron lasers. It provides inherently synchronized femtosecond laser ‘pump’ and X-ray ‘probe’ pulses to enable time-resolved diffraction and absorption experiments. By using X-ray diffraction to probe laser-induced coherent optical phonons in bulk bismuth, we estimate an X-ray pulse duration of 140 ± 30 fs FWHM with timing drifts below 30 fs rms measured over 5 days. The excellent spatial and temporal stability of the source allows quantitative measurement of ultrafast lattice dynamics and associated phase transitions in real space with atomic resolution and instrumental time resolution of 85 fs rms. Studying semimetals such as bismuth, we have demonstrated (i) grazing incidence femtosecond X-ray diffraction on single crystals that allows us to more completely characterize the ultrafast structural dynamics of solids, and (ii) optical control of real space coherent atomic motion. Both methods will be used to study the dynamics of photo-induced phase transitions in strongly correlated systems such as manganites. The time resolution of such measurements could be improved by one order of magnitude at future XFEL facilities at much higher flux. Femtosecond linear and non-linear resonant X-ray scattering employing full polarization control both in the soft (0.3–3 keV) and hard (4–15 keV) X-ray regime will become feasible which allows direct measurement of orbital degrees of freedom. However, a laser and hard X-ray cross-correlation technique with sufficient temporal resolution and signal-to-noise ratio appropriate for single shot operation has yet to be realized. Again, laser seeding using a phase stabilized few-cycle (5–7 fs) laser may be a viable option to generate <10 fs X-ray pulses.

September 25, 2009

Exploiting EXAFS and XANES for time-resolved molecular structures in liquids

Christian Bressler, Rafael Abela, Majed Chergui

Page range: 307-321

Abstract

Time-resolved X-ray absorption fine structure (XAFS) spectroscopy with picosecond temporal resolution is a new method to observe electronic and geometric structures of short-lived reaction intermediates. It combines an intense femtosecond laser source synchronized to the X-ray pulses delivered by a synchrotron Swiss light source (SLS). We present key experiments on charge transfer reactions as well as spin-crossover processes in coordination chemistry compounds next to solvation dynamics studies of photogenerated atomic radicals. These examples emphasize the observables at hand using ultrafast XAFS techniques, which include the density of states, full and even partial changes in oxidation state, and internuclear distances with milli-Angström accuracy. An outlook towards femtosecond studies and biologically relevant systems stresses the high potential of XAFS methods using new femtosecond X-ray sources like free electron lasers (XFELs).

September 25, 2009

Home-based time-resolved photo small angle X-ray diffraction and its applications

Wilson Quevedo, Marcel Petri, Simone Techert

Page range: 322-328

Abstract

An experimental outline will be given for home-based time-resolved photo small angle X-ray diffraction apparatus. Depending on the time-resolution of the optical laser excitation source, the readout time of the detector and their relative time jitter, time resolutions down to some hundred microseconds might be achieved. Even though the X-ray flux might be low, as expected for sealed tube kind of sources, experiments with a sufficient signal/noise ratio can be performed by applying a stroboscopic mode. The method of photo small angle X-ray scattering will be applied to photo-sensitized liquid crystal systems demonstrating the possibility of photo-inducing a phase transition between a liquid crystal and a microemulsion phase in this type of material.

September 25, 2009

DFT study of crystalline nitrosyl compounds

Bernard Delley

Page range: 329-333

Abstract

Nitrosyl linkage isomer compounds are investigated with density functional theory for realistic crystal structures. As compared to free anion models, significant differences are found for various properties. At the metastable state S1, a crystal environment contribution of 30–40 cm −1 to the red shift exists. The barrier against thermal decomposition of S1 in SNP is significantly lowered by 300 meV.

September 25, 2009

Theoretical study on the structure of the ground state and photo-induced metastable states of [M(CN)₅NO]²⁻ (M = Ru, Fe), and mechanism of the photo-rearrangement among them

Takeshi Ishikawa, Kiyoshi Tanaka

Page range: 334-342

Abstract

In this note, we reviewed theoretical investigations of the photo-induced metastable states and discussed possible photo-rearrangement paths in [M(CN) 5 NO] 2− (M = Fe and Ru). Using calculated results of ab initio multi-reference single and double excitation configuration interaction calculations with Davidson type quadruple correction (MRSDCI + Q) and those of density fuctional theory (DFT), we showed that the two metastable states (MS1 and MS2) were local minima of the electronic ground state potential surface. The theoretical calculations supported the experimental observation of the structure of the three isomers (GS, MS1 and MS2), relative stability of MS1 and MS2. We discussed the character of the lower electronic excited states and excitation energies of the three isomers of both compounds. Based on these results and excited state adiabatic potential energy surfaces, possible mechanism of photo-rearrangement among GS, MS1, and MS2 were discussed with the aid of our results on [Mn(CN) 5 NO] 3− of which no photo-rearrangement has been reported.

September 25, 2009

DFT study of metastable linkage isomers of six-coordinate ruthenium nitrosyl complexes

Olga V. Sizova, Olga O. Lubimova, Vladimir V. Sizov, Nina V. Ivanova

Page range: 343-355

Abstract

The linkage isomers of the [M(NO)(CN) 5 ] 2− (M = Fe, Ru, Os), [Ru(NO)Cl 5 ] 2− , trans-[Ru(NO)(NH 3 ) 4 (L)] q+ (L = NH 3 , H 2 O, nicotinamide, imidazole, pyridine, pyrazine, NO 2 − , OH − , Cl − ), and trans-[Ru(NO)L 4 (OH)] q (L = pyridine, NO 2 − ) ions are studied by density functional theory. DFT calculations show that the electronic ground-state potential surface of these nitrosyl complexes has the local minima corresponding to η 2 -NO and η 1 -O linkage isomers, of which the former is characterized by lower energy. The stationary points on the ground state potential energy surface along the GS → MS2 → MS1 path for the [M(NO)(CN) 5 ] 2− (M = Fe, Ru, Os) and [Ru(NO)Cl 5 ] 2− complexes were found. The calculations of infrared spectra of linkage isomers [Ru(NO)Cl 5 ] 2− and [Ru(NO)(CN) 5 ] 2− are carried out. The analysis of quantum chemical bond orders indicates a noticeable delocalization of π-electron density along the L trans —M—NO axis and a possibility of direct interactions between NO and equatorial ligands in the structures with the bent {MNO} group.

September 25, 2009

Excited state isomerization in photochromic ruthenium complexes

Jeffrey J. Rack

Page range: 356-362

Abstract

Photochromic ruthenium polypyridyl complexes whose action is based on an excited state linkage isomerization are discussed. Picosecond transient absoption spectroscopic data indicate that isomerization occurs along the charge-transfer manifold. These studies indicate that rotation about the Ru–S bond is an important vibration along this coordinate. These complexes are of interest in photonic molecular devices, specifically molecular information storage applications.

September 25, 2009

Applications of photocrystallography: a future perspective

Jacqueline M. Cole

Page range: 363-369

Abstract

The applied potential of photocrystallography is discussed herein. In particular, its ability to help realise new generation ‘smart’ materials for the opto-electronics industry, alternative photovoltaic solar cells, and health science, is discussed. Where relevant photocrystallographic studies have already been reported, examples are given and put into the context of potential device applicability. In certain areas of photonics research, there are no current photocrystallographic results specifically pertaining to the perceived application described. Here, the likely type of results is projected since this perspective is designed deliberately to look ahead as to what advances photo-crystallography could bring to the photonics research area that continues to develop so rapidly. Brief reference to global economic, environmental and health considerations are also made in relevant places in order to put the subject onto a world setting.

About this journal

Objective
Zeitschrift für Kristallographie – Crystalline Materials was founded in 1877 by Paul von Groth and is today one of the world’s oldest scientific journals. It offers a place for researchers to present results of their theoretical experimental crystallographic studies. The journal presents significant results on structures and on properties of organic/inorganic substances with crystalline character, periodically ordered, modulated or quasicrystalline on static and dynamic phenomena applying the various methods of diffraction, spectroscopy and microscopy.

Topics

General Aspects
Inorganic Crystal Structures
Organic and Metalorganic (including Biological)
Crystal Structures
Technological Aspects
Computer Programs
Instrumentation
Material Properties

Article formats
Letters, Reviews, Original Papers, Discussions, Book Reviews

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Volume 223 Issue 4-5 - Photocrystallography

Issue of Zeitschrift für Kristallographie - Crystalline Materials

Preface: Photocrystallography

Out-of-equilibrium charge density distribution of spin crossover complexes from steady-state photocrystallographic measurements: experimental methodology and results

Abstract

Light-induced phase separation (LIPS) into like-spin phases observed by Laue neutron diffraction on a single crystal of [Fe(ptz)6](BF4)2

Abstract

Neutron photocrystallography: simulation and experiment

Abstract

Static and time-resolved photocrystallographic studies in supramolecular solids

Abstract

State of the art and opportunities in probing photoinduced phase transitions in molecular materials by conventional and picosecond X-ray diffraction

Abstract

Real-time studies of reversible lattice dynamics by femtosecond X-ray diffraction

Abstract

Towards pump-probe resonant X-ray diffraction at femtosecond undulator sources

Abstract

Exploiting EXAFS and XANES for time-resolved molecular structures in liquids

Abstract

Home-based time-resolved photo small angle X-ray diffraction and its applications

Abstract

DFT study of crystalline nitrosyl compounds

Abstract

Theoretical study on the structure of the ground state and photo-induced metastable states of [M(CN)5NO]2− (M = Ru, Fe), and mechanism of the photo-rearrangement among them

Abstract

DFT study of metastable linkage isomers of six-coordinate ruthenium nitrosyl complexes

Abstract

Excited state isomerization in photochromic ruthenium complexes

Abstract

Applications of photocrystallography: a future perspective

Abstract

Light-induced phase separation (LIPS) into like-spin phases observed by Laue neutron diffraction on a single crystal of [Fe(ptz)₆](BF₄)₂

Theoretical study on the structure of the ground state and photo-induced metastable states of [M(CN)₅NO]²⁻ (M = Ru, Fe), and mechanism of the photo-rearrangement among them