Purely organic luminescent molecules with long-lived excited states gained a certain amount of interest, due to their wide range of optoelectronic applications.The environment friendliness, non-toxicity and low cost also brought favourable attention over their inorganic counterparts.However, the benefit of using organic phosphorescent materials have been limited by their extreme sensitivity towards the surrounding environment (humidity and temperature) and fast non-radiative quenching.Nonetheless, a number of recent studies on purely organic phosphorescent molecules with unusually short Br...Br intermolecular contact distances have been reported.[1] We have also recently reported the excited state geometry of a Br containing purely organic phosphorescent molecule, studied by means of In-House Time Resolved X-Ray Diffraction.[2] The molecule shows strong luminescence only in solid state when excited at 355nm and does not show any emission in dilute dichloromethane solution.Shi et al. claims the presence of several deactivation processes (non-radiative decay, collisional quenching by oxygen and other impurities) caused this lack of luminescence in solution.We also observed an increment in the Br…Br intermolecular contact distance from 3.29Å (GS) to 3.38Å (ES), in crystals upon light induced excitation at 90K (Figure 1a).It seems that short Br…Br intermolecular interactions may have an important role in causing these molecules to be luminescent in solid state.Recently a series of molecules with short Br…Br intermolecular contacts have been reported (Figure 1b).[3]But most of these studies do not go beyond the crystal structure determination.We are synthesizing some and measuring their photo-physical properties.As the rapid improvement in the brightness of X-ray sources and the sensitivity of detectors, enables the use of laboratory equipment to explore short-lived excited state geometries in molecular crystals, the importance of this technique for the above mentioned class of purely organic luminophores cannot be ignored.

A short description of some of the paradigm-changing developments of the study of light-induced structural changes in molecular crystals is presented. The review is by no means comprehensive. The extensive literature on the subject should be consulted for further information.

The structural changes accompanying the excitation of the luminescent dibromobenzene derivative, 1,4-dibromo-2,5-bis(octyloxy)benzene, have been measured by in-house monochromatic time-resolved (TR) diffraction at 90 K. Results show an increment of the very short intermolecular Br•••Br contact distance from 3.290 Å to 3.380 Å. Calculations show the Br…Br interaction to be strongly repulsive in both the Ground and Excited states but significantly relaxed by the lengthening of the contact distance on excitation. The stability of the crystals is attributed to the many weak C-H···Br and C-H···π intermolecular interactions. The study described is the first practical application of In-House Time-Resolved diffraction, made possible by the continuing increase in the brightness of X-ray sources and the sensitivity of our detectors.

In picosecond and slower pump–probe diffraction experiments, collection of response–ratio correlation sets prior to full data collection provides an invaluable confirmation of the existence of a light-induced signal prior to full data collection. If a response to light exposure is observed, the quality of the data being collected can be assessed. A number of such correlation plots both for synchrotron and in-house pump–probe data collection are presented.

Two methods for scaling of multicrystal data collected in time-resolved photocrystallography experiments are discussed. The WLS method is based on a weighted least-squares refinement of laser-ON/laser-OFF intensity ratios. The other, previously applied, is based on the average absolute system response to light exposure. A more advanced application of these methods for scaling within a data set, necessary because of frequent anisotropy of light absorption in crystalline samples, is proposed. The methods are applied to recently collected synchrotron data on the tetra-nuclear compound Ag2Cu2L4 with L = 2-diphenylphosphino-3-methylindole. A statistical analysis of the weighted least-squares refinement residual terms is performed to test the importance of the scaling procedure.

A summary of the evidence based on spectroscopy, calculated density of states (DOS) and photo-electrochemistry, for electron transfer from the occupied Fe(2+) (d)-β orbital located within the band gap of the [Ti4 O(OEt)15 (FeBr)] cluster, to its unoccupied Ti(d) orbitals is presented. The importance of the distinction between the concepts of band gap and HOMO-LUMO gap is emphasized.

Fast hole hopping in Til7cat4, a 1 nm diameter molecular polyoxotitanate cluster bearing four catechol ligands (Ti-17(mu(4)-O)(4)(mu(3)-O)(16)(mu(2)-O)(4)(cat)(4)(OPri)(16)), was investigated by ultrafast spectroscopy and quantum dynamics simulations. The catechol moieties coupled to the TiO2 core of the cluster give rise to a charge-transfer band, the excitation of which promotes an electron from the highest occupied molecular orbital of the ligand to the inorganic core, resulting in the formation of {cat(+center dot),Ti3+}, a vibrationally hot polaronic exciton. Dynamic depolarization measurements indicate that within less than 100 fs the Franck-Condon polaronic state formed at the interface evolves into a fully charge-separated state and the injected electron delocalizes over the quasi conduction band of the cluster. The positive charge (hole) resulting from the injection does not remain static either. The initial hole hopping between the catechol sites occurs with the rate of similar to 5 X 10(11) s(-1) or more and competes with the intramolecular vibrational relaxation. Upon thermalization, the hopping slows and continues at a rate of similar to 5 X 10(10) s(-1). The experimentally observed rate of hole hopping agrees well with the results of quantum dynamics modeling of the wavepacket propagation.

Recent studies have produced experimental triplet excited state structures with lifetimes of nanoseconds to microseconds. Photodifference maps, showing the total change on excitation, in principle include both the effect of the atomic shifts on excitation and that of the orbital transitions. The latter can be calculated theoretically thus achieving a formal deconvolution of the atomic and electronic shifts. In the three examples presented electronic shifts on excitation are orders of magnitude smaller than the effect of the atomic shifts and their electron shells and therefore not experimentally accessible at this time.

In the paper by Kamiński et al. [ J. Appl. Cryst. (2014), 47 , 1765–1768], Jason B. Benedict is missing from the list of authors. The complete list of authors should be Radosław Kamiński, Jason B. Benedict, Gary Nottingham and Philip Coppens.

Density functional theory calculations reveal that the previously unreported nitrosothiol MS1 and MS2 linkage isomers are metastable species with energies similar to those determined for other experimentally observed XNO linkage isomers. Nitrosation of protein cysteines to yield S-nitrosocysteine (cySNO) is an important component of nitric oxide biology. However, high-resolution structural data of cySNO in the absence of protein environment effects is lacking, as is information on cySNO linkage isomers. We report the ordered X-ray crystal structure of a cySNO compound. We employ density functional theory calculations to probe the ground-state and linkage isomers of cySNO, CH3SNO, and CF3SNO. The HOMO of CH3SNO contains an intramolecular CH···O interaction that helps rationalize the stability of the cis conformation; this interaction is absent in CF3SNO, which favors the trans conformation. We show that the isonitroso MS1 (RSON) and side-on MS2 (RS(η2-ON)) linkage isomers are metastable species, with MS1 and MS2 energies similar to those of other experimentally observed nitroso linkage isomers. GRAPHICAL ABSTRACT

Homodisperse doped polyoxotitanate nanoclusters with formulae Ti11 (MX)O14 (OiPr)17 (M=Mn, Fe or Co; X=Cl, Br or I, OiPr=isopropoxide) display strongly dopant-dependent properties. Spectroscopic solution and reflectance measurements backed up by density of states and time-dependent DFT calculations based on the determined structures, show the prominent effect of FeX substitution by decreasing the HOMO-LUMO gap of the particles. The effect is attributed to the presence of an occupied Fe β orbital halfway up the bandgap, leading to long-wavelength absorption with electron transfer to the titanium atoms of the cluster. Whereas the light absorption varies significantly with variation of the transition metal dopant, its dependency on the nature of the halogen atom or the change in dipole moment across the series is minor.

The need for data-scaling has become increasingly evident as time-resolved pump-probe photocrystallography is rapidly developing at high intensity X-ray sources. Several aspects of the scaling of data sets collected at synchrotrons, XFELs (X-ray Free Electron Lasers) and high-intensity pulsed electron sources are discussed. They include laser-ON/laser-OFF data scaling, inter- and intra-data set scaling.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Newly developed methods for time-resolved studies using the polychromatic and in particular the pink-Laue technique, suitable for medium and small-size unit cells typical in chemical crystallography, are reviewed. The order of the sections follows that of a typical study, starting with a description of the pink-Laue technique, followed by the strategy of data collection for analysis with the RATIO method. Novel procedures are described for spot integration, orientation matrix determination for relatively sparse diffraction patterns, scaling of multi-crystal data sets, use of Fourier maps for initial assessment and analysis of results, and least-squares refinement of photo-induced structural and thermal changes. In the calculation of Fourier maps a ground-state structure model, typically based on monochromatic results, is employed as reference, and the laser-ON structure factors for the Fourier summations are obtained by multiplying the reference ground-state structure factors by the square root of the experimental ON/OFF ratios. A schematic of the procedure followed is included in the conclusion section.

Highlights of my scientific experiences during a golden age of science in which new avenues were opened due to an unprecedented increase in experimental and computational facilities are summarized.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

The paper collects the answers of the authors to the following questions: " What is the significance of topological approach?Can new chemical concepts be found by a topological approach?What is the status of a chemical concept within a topological approach?Should topological approaches provide measurable quantities?Is it possible to predict the outcome of a topological approach without performing a calculation on a computer?What are new domains for which topological approaches would be useful? (C) 2014 Elsevier B.V. All rights reserved.