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Ru(II) and Ir(III) complexes containing ADA and DAD triple hydrogen bonding motifs: Potential tectons for the assembly of functional materials.
摘要： The synthesis and characterisation of series of [Ru(II)(bpy)2L] and [Ir(ppy)2L] complexes containing ligands L with the potential to engage in triple hydrogen bonding interactions is described. L1 and L2 comprise pyridyl triazole chelating units with pendant diaminotriazine units, capable of donor-acceptor-donor (DAD) hydrogen bonding, while L3 and L4 contain ADA hydrogen bonding units proximal to N^N and N^O cleating sites, respectively. X-ray crystallography shows the L1 and L2 containing Ru(II) complexes to assemble via R22(8) hydrogen bonding dimers, while [Ru(II)(bpy)2L4] assembles via extended hydrogen bonding motifs to form one dimensional chains. By contrast, the expected hydrogen bonding patterns are not observed for the Ru(II) and Ir(III) complexes of L3. Spectroscopic studies show that the absorption spectra of the complexes result from combinations of MLCT and LLCT transitions. The L1 and L2 complexes of Ir(III) and Ru(II) complexes are emissive in the solid state and it seems likely that hydrogen bonding to complementary species may facilitate tuning of their 3ILCT emission. Low frequency Raman spectra provide further evidence for ordered interactions in the solid state for the L4 complexes, consistent with the results from X-ray crystallography.
关键词： crystal engineering,ruthenium,Hydrogen bonding,iridium,X-ray crystallography
更新于2025-09-23 15:23:52
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Constituent substitution in hot wall deposition of Bi2S3 films by reaction with substrates
摘要： Replacement of a constituent in the overgrown layers with the materials provided by the substrates is investigated when Bi2S3 films are deposited on III-V compound semiconductors and transition metals using a hot wall epitaxy method. The substitution caused by the S atoms is stronger than that by the Se and Te atoms in deposition of Bi2Se3 and Bi2Te3 films. Mere exposure to Bi2S3 vapor of In-containing compounds (InP and InAs) and Ga-containing compounds (GaAs and GaSb) at epitaxial growth temperatures results in a capping of their surfaces by In2S3 and GaS, respectively. A temperature window is revealed to exist for the GaAs case where growth of Bi2S3 microcrystals occurs within the temperature range for the sulfide formation. The sulfurization by the material substitution is thus demonstrated to be not always identical with that using elemental sulphur. We examine furthermore the sulfides synthesized on the surfaces of Cu, Ag, Ni, Mo, and W. The sulfides produced on Cu and Ag undergo material alterations when they are irradiated by a laser light.
关键词： X-ray crystallography,Hot wall epitaxy,Material substitution,Raman spectroscopy,Bi2S3,Sulfides
更新于2025-09-23 15:22:29
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Molecular and excited state properties of photostable anthraquinone blue dyes for hydrophobic fibers
摘要： Synthetic dyes having high photostability on hydrophobic fibers such as poly(ethylene terephthalate) (PET) are of interest for use on textile substrates for outdoor applications. While much is known about photostable dyes developed for PET in the 1980s, owing to their viability for use in automobile interiors, little has been published on currently viable photostable disperse dyes. As part of an effort to help fill this void and to facilitate future photostable disperse dye design, the present study involved the use of experimental measurements and modelling studies to help characterize the molecular structures of commercially viable dyes for producing photostable colors on PET fibers, beginning with a pair of blue dyes. With the aid of HR-MS, 500 MHz 1H NMR, and X-ray crystallography, it was established that the two dyes are structural isomers having 1,5-(OH)2-anthraquinone (AQ) and 1,8-(OH)2-AQ base structures. It is proposed that the photostability of these dyes arises from the presence of multiple OH/NH groups ortho to the AQ C]O groups which enables them to dissipate excited state energy through intramolecular proton transfer. Further, using DFT-based molecular modelling studies, it was shown that the dye having the 1,5-(OH)2-AQ base structure has a lower ESOP than the isomeric dye having the 1,8-(OH)2-AQ base structure. Similarly, results from calculating Frontier HOMO and LUMO isosurfaces indicated that the LUMO lobes of the latter dye are larger, suggesting that this dye undergoes excitation faster than the 1,5-(OH)2-AQ isomer.
关键词： Molecular modelling,Anthraquinone disperse dyes,X-ray crystallography,Intramolecular H-bonding,Structural analysis
更新于2025-09-23 15:22:29
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Possibilities for serial femtosecond crystallography sample delivery at future light sourcesa)
摘要： Serial femtosecond crystallography (SFX) uses X-ray pulses from free-electron laser (FEL) sources that can outrun radiation damage and thereby overcome long-standing limits in the structure determination of macromolecular crystals. Intense X-ray FEL pulses of sufficiently short duration allow the collection of damage-free data at room temperature and give the opportunity to study irreversible time-resolved events. SFX may open the way to determine the structure of biological molecules that fail to crystallize readily into large well-diffracting crystals. Taking advantage of FELs with high pulse repetition rates could lead to short measurement times of just minutes. Automated delivery of sample suspensions for SFX experiments could potentially give rise to a much higher rate of obtaining complete measurements than at today’s third generation synchrotron radiation facilities, as no crystal alignment or complex robotic motions are required. This capability will also open up extensive time-resolved structural studies. New challenges arise from the resulting high rate of data collection, and in providing reliable sample delivery. Various developments for fully automated high-throughput SFX experiments are being considered for evaluation, including new implementations for a reliable yet flexible sample environment setup. Here, we review the different methods developed so far that best achieve sample delivery for X-ray FEL experiments and present some considerations towards the goal of high-throughput structure determination with X-ray FELs.
关键词： automation,serial femtosecond crystallography,X-ray free-electron laser,sample delivery,high-throughput
更新于2025-09-23 15:22:29
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Ferroelectric Origin and Distortion Modes in Doped BiFeO <sub>3</sub> by Crystallography Approach
摘要： There are conflicts about the ferroelectric origin and the relationship of two distortion modes, namely, the ferroelectric (FE) mode and antiferrodistortive (AFD) mode. Here the two distortion modes and enhanced ferroelectric properties (Pr=89.5 μC cm-2) are observed in BiFeO3 thin films doped with small radius Mg2+ (A-site) deposited on (111) Pt/Ti/SiO2/Si substrates by a sol-gel method, the relationship of the two distortion modes turns from cooperative to competitive as the FE mode strengthens. A new explanation of ferroelectric origin and distortion modes in doped BiFeO3 by the Defect Dipoles Driven Distortions Theory (abbreviate DDD) from crystallography is reported. Meanwhile, the crystal structure regulation mechanism of doped BiFeO3 thin films with substantially enhanced ferroelectric properties is also put forward. The distances of the positive and negative charge center in [FeO6] octahedrons evidently increase by Mg2+ doping compared with that in the Bi0.9Sm0.1Fe0.95Mn0.05O3 (BSFMO). The change of distances is contributed to the law of the atomic migration from the move of oxygen vacancies and the attraction of defect dipoles. A positive effect on ferroelectric properties of the appropriate increase in oxygen vacancies is explored, which is explained by "the probability of possible position that oxygen vacancies occurred" and "the relationship between the leakage current and the overlapping oxygen positions". The potential structure and more suitable doping ions are successfully predicted by the crystal structure regulation mechanism. In addition, it brings a new direction for the search of other structure regulation ions so as to realize the perfect ferroelectric properties for practical application, which will become an important beginning of ferroelectric materials design.
关键词： ferroelectric properties,structural distortions,crystallography,ferroelectric origin,defect dipoles
更新于2025-09-23 15:22:29
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In-situ measurement of surface relief induced by Widmanst?tten and bainitic ferrites in low carbon steel by digital holographic microscopy
摘要： In-situ measurement by digital holographic microscopy (DHM) was employed to clarify the difference between the surface relief effects of Widmanst?tten ferrite (WF) and bainitic ferrite (BF) associated with their transformations from austenite in a low-carbon steel. It was clarified that the evolution of the surface relief is totally different between WF and BF. Only in BF, the observed ratio of the relief height to the plate width converged instantly to the value predicted by the phenomenological theory of martensite crystallography (PTMC). The ratio gradually increased with increasing plate thickness and never reached the value predicted by PTMC in WF.
关键词： Digital holographic microscopy,Phase transformations,Surface relief,Phenomenological theory of martensite crystallography
更新于2025-09-23 15:21:21
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A genetically encoded photosensitizer protein facilitates the rational design of a miniature photocatalytic CO2-reducing enzyme
摘要： Photosensitizers, which harness light energy to upgrade weak reductants to strong reductants, are pivotal components of the natural and artificial photosynthesis machineries. However, it has proved difficult to enhance and expand their functions through genetic engineering. Here we report a genetically encoded, 27 kDa photosensitizer protein (PSP), which facilitates the rational design of miniature photocatalytic CO2-reducing enzymes. Visible light drives PSP efficiently into a long-lived triplet excited state (PSP*), which reacts rapidly with reduced nicotinamide adenine dinucleotide to generate a super-reducing radical (PSP?), which is strong enough to reduce many CO2-reducing catalysts. We determined the three-dimensional structure of PSP? at 1.8 ? resolution by X-ray crystallography. Genetic engineering enabled the site-specific attachment of a nickel–terpyridine complex and the modular optimization of the photochemical properties of PSP, the chromophore/catalytic centre distance and the catalytic centre microenvironment, which culminated in a miniature photocatalytic CO2-reducing enzyme that has a CO2/CO conversion quantum efficiency of 2.6%.
关键词： quantum efficiency,photosensitizer protein,visible light,photocatalytic CO2-reducing enzymes,X-ray crystallography,nickel–terpyridine complex,genetic engineering
更新于2025-09-23 15:21:01
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Investigating the Photochemistry of Spiropyran Metal Complexes with Online LED-NMR
摘要： As one of the best studied photoswitches, spiropyrans (SPs) have attracted significant interest in the scientific community. Among the many stimuli to alter the isomerization into the merocyanine (MC) isomer, such as temperature, pH, solvent polarity, redox potential, or mechanical force, the ability of the MC form to act as a ligand site for metal complexation has recently raised new attention. We herein synthesize hitherto undescribed coordination compounds of 8-methoxy-1′,3′,3′-trimethyl-6-nitrospiro-[chromene-2,2′-indoline] with s-block ([Ca(MC)4](ClO4)2), d-block ([Zn(MC)2(MeCN)2](ClO4)2, [Ni(MC)2(MeCN)2](ClO4)2), as well as f-block ([La(NO3)3(MC)2]) metals. All complexes are structurally described by X-ray crystallography and systematically investigated in solution via Job’s method of continuous variations (Job plots), as well as online NMR spectroscopic kinetic experiments with in situ irradiation of the analyte solution inside the NMR spectrometer (LED-NMR). We can unambiguously identify the photoresponsive nature of the complexes in solution, which is a crucial step toward the application of these promising molecules in material science.
关键词： photochemistry,LED-NMR,metal complexes,X-ray crystallography,spiropyrans
更新于2025-09-23 15:19:57
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Demonstration of Large Bandwidth Hard X-Ray Free-Electron Laser Pulses at SwissFEL
摘要： We have produced hard x-ray free-electron laser (FEL) radiation with unprecedented large bandwidth tunable up to 2%. The experiments have been carried out at SwissFEL, the x-ray FEL facility at the Paul Scherrer Institute in Switzerland. The bandwidth is enhanced by maximizing the energy chirp of the electron beam, which is accomplished by optimizing the compression setup. We demonstrate continuous tunability of the bandwidth with a simple method only requiring a quadrupole magnet. The generation of such broadband FEL pulses will improve the efficiency of many techniques such as x-ray crystallography and spectroscopy, opening the door to significant progress in photon science. It has already been demonstrated that the broadband pulses of SwissFEL are beneficial to enhance the performance of crystallography, and further SwissFEL users plan to exploit this large bandwidth radiation to improve the efficiency of their measurement techniques.
关键词： large bandwidth,SwissFEL,free-electron laser,spectroscopy,hard x-ray,x-ray crystallography
更新于2025-09-23 15:19:57
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Low-Energy Electronic Transition in SiB Rings
摘要： Five- and six-membered rings containing Si?B bonds were synthesized by salt metathesis of magnesium disilanides with tetramethylpiperidinyldichloroborane (TMPBCl2). Materials were characterized by 1H, 11B, 13C, and 29Si NMR spectroscopy, as well as X-ray crystallography. Insights from crystallography facilitate conformational analysis of the cyclosilanes and elucidation of conformation-dependent optical properties. Crystallography also supports assignment of π character to the BN bond of the tetramethylpiperidinylborane fragment. The SiB rings have unique optical properties compared to all silicon rings. A 350 nm electronic transition only observed in SiB rings is assigned to a σ?π* transition on the basis of density functional theory calculations.
关键词： density functional theory,salt metathesis,σ?π* transition,NMR spectroscopy,X-ray crystallography,Si?B rings
更新于2025-09-23 15:19:57