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Exploring the surface chemistry of cesium lead halide perovskite nanocrystals
摘要： Colloidal nanocrystals (NCs) of cesium lead halide perovskites (CsPbX3, X = Cl, Br or I) are emerging as an exciting class of optoelectronic materials, but the retention of their colloidal and structural integrity during isolation, purification and handling still represents a critical issue. The impelling questions concerning their intrinsic chemical instability are connected to the dynamic nature of the bonding between the inorganic surface and the long-chain capping ligands. However, the key aspects of CsPbX3's surface chemistry that directly impact their stability remain elusive. In this contribution, we provide an in-depth investigation of the surface properties of differently composed CsPbX3 NCs, prepared by traditional hot-injection methods. The study, mainly relying on solution NMR spectroscopy, is backed up by elemental analysis as well as morphological, structural and optical investigations. We ascertained that the nature of the ligand adsorption/desorption processes at the NC surface is dependent on its elemental composition, thus explaining the origin of the instability afflicting CsPbI3 NCs. We also evaluated the effect of NC purification as well as of the degradation pathways involving the organic shell on the surface chemistry of CsPbX3 NCs. This study paves the way for new post-functionalization strategies for this promising class of nanomaterials.
关键词： surface chemistry,colloidal stability,degradation pathways,cesium lead halide perovskite nanocrystals,purification,ligand adsorption/desorption,NMR spectroscopy
更新于2025-09-19 17:15:36
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1H NMR study of molecular order and dynamics in CBC9CB Liquid Crystal
摘要： Molecular order and dynamics of the CB-C9-CB liquid crystalline dimer exhibiting the nematic (N) and the twist bend nematic (Ntb) phases were investigated by proton NMR spectroscopy, using fields of 0.78 T and 7.04 T, and relaxometry. The first relaxometry experiments for a very wide Larmor frequency domain (8 kHz - 300 MHz) on this system, using a combination of standard and fast field cycling NMR techniques, were performed. The spectroscopy results in the Ntb phase allowed us to probe the local molecular orientation relative to the Ntb helix axis. The relaxation data were analyzed considering order director fluctuations (ODF), molecular self-diffusion (SD) and local molecular rotations/reorientations (R) relaxation mechanisms. Global fits of theoretical relaxation models, as a function of temperature and Larmor frequency, for the phases under investigation, allowed for the determination of rotational correlation times, diffusion coefficients, viscoelastic parameters, correlation lengths and activation energies (in the case of thermally activated mechanisms). A clear difference between the structures of the N and Ntb phases was detected from the results of proton spin-lattice relaxation through distinct temperature and frequency dependencies' signatures of the collective modes. Significant pre-transitional effects were observed at the N-Ntb phase transition both from relaxometry and spectroscopy data. The experimental results correlate to data and models for comparable liquid crystalline systems.
关键词： molecular dynamics,liquid crystal,nematic phase,twist bend nematic phase,NMR spectroscopy,relaxometry
更新于2025-09-19 17:15:36
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Synthesis and Characterization of a Rare Transition-Metal Oxothiostannate and Investigation of Its Photocatalytic Properties
摘要： The new transition-metal oxothiostannate [Ni(cyclen)(H2O)2]4[Sn10S20O4]·～13H2O (1) was prepared under hydrothermal conditions using Na4SnS4·14H2O as the precursor in the presence of [Ni(cyclen)(H2O)2](ClO4)2·H2O. Compound 1 comprises the [Sn10S20O4]8? anion constructed by the T3-type supertetrahedron [Sn10S20] and the [Sn10O4] anti-T2 cluster. Channels host the H2O molecules, and the sample can be reversibly dehydrated and rehydrated without significantly affecting the crystallinity of the material. 119Sn NMR spectroscopy of an aqueous solution of Na4SnS4·14H2O evidences that between 25 and 120 °C only [SnS4]4? and [Sn2S6]4? anions are present. In further experiments, hints were found that the formation of the tin oxosulfide ions depends on the Ni2+-centered complexes. Compound 1 exhibits promising photocatalytic properties for the visible-light-driven hydrogen evolution reaction, with 18.7 mmol·g?1 H2 being evolved after 3 h.
关键词： photocatalytic hydrogen evolution,oxothiostannate,NMR spectroscopy,hydrothermal synthesis,transition-metal complex
更新于2025-09-19 17:15:36
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Controlled synthesis of unsubstituted high molecular weight poly( <i>para</i> -phenylene) <i>via</i> Suzuki polycondensation-thermal aromatization methodology
摘要： Suzuki polycondensation-thermal aromatization methodology was developed as a versatile new route to structurally regular, unsubstituted high molecular weight poly(para-phenylene) (PPP). The utility of this methodology was demonstrated by synthesizing PPP from both cis- and trans-precursor prepolymers 1a-b. The structure of precursor prepolymers containing exclusively 1,4-repeating units with the hydroxyphenyl group at the chain end was determined by two-dimensional NMR spectroscopy. Pyrolysis of trans-poly(para-phenylene) precursor 1b resulted in complete aromatization to PPP containing an average of 110 phenylene units in the polymer chain. The thermal conversion of precursor polymers to polyphenylene is a straightforward process leading to pristine PPP without significant chain degradation as confirmed by solid-state NMR and TGA analysis. The characterization of PPP by solid-state NMR, UV-vis absorption, fluorescence emission and IR spectroscopy, TGA, and conductivity measurements exhibits significant features for electronic and photoelectronic application, such as broadened absorption, high thermal stability, and typical conducting properties.
关键词： Suzuki polycondensation,NMR spectroscopy,high molecular weight,Poly(para-phenylene),thermal aromatization
更新于2025-09-19 17:13:59
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Dynamical processes related to viscous flow in a supercooled arsenic selenide glass-forming liquid: Results from high-temperature 77Se NMR spectroscopy
摘要： Dynamical processes in supercooled AsSe9 liquid are studied using 1D and 2D 77Se NMR spectroscopic techniques. The results demonstrate the coexistence of two distinct dynamical processes: one is a slow process related to the chemical exchange between the various Se environments by bond scission/renewal and the other is the fast Se chain segmental motion, which leads to the rapid averaging of the chemical shift anisotropy. The timescales of these two processes become increasingly similar as the glass transition is approached from above. The slow process is found to be closely coupled to viscosity over the entire temperature range of investigation and its activation energy is consistent with the Se-Se/As bond energies. On the other hand, the activation energy of the fast process is significantly higher, which may be indicative of its cooperative nature. This process becomes coupled to viscosity only in the immediate vicinity of the glass transition.
关键词： Supercooled liquid,Relaxation,Chalcogenide,Viscous flow,Glass transition,NMR spectroscopy
更新于2025-09-11 14:15:04
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Radical induced cationic frontal twin polymerization of Si-spiro compound in combination with bisphenol-A-diglycidylether
摘要： The radical induced cationic frontal polymerization (RICFP) of the twin monomer with 2,2’-spirobi[4H-1,3,2-benzodioxasiline] combination (SPIRO) in bisphenol-A-diglycidylether (BADGE) has been developed to fabricate nanostructured hybrid material with domain sizes of 2–5 nm. In one reaction step, an interpenetrating network of phenolic resin, SiO2 and the epoxy resin is formed in a very short time period, initiated by UV light. That indicates that both polymerization reactions take place simultaneously. The influence of monomer composition on molecular structure was investigated by means of solid state NMR spectroscopies. The envisaged nanostructure of the resulting organic-inorganic hybrid materials is proven by transmission electron microscopy high-angle annular dark-field scanning (HAADF-STEM). The thermal properties of the hybrid materials are comparable to “state of the art” materials with the advantage that the silica quantity can be adjusted on demand.
关键词： Nanostructured hybrid material,HAADF-STEM,Solid state NMR spectroscopy,Radical induced cationic frontal polymerization,Twin polymerization
更新于2025-09-11 14:15:04
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The effect of the length of terminal n-alkyl carboxylate chain on self-assembling and photosensitive properties of chiral lactic acid derivatives
摘要： A new series of photosensitive azo materials possessing a chiral alkyl lactate moiety and terminal n-alkyl carboxylate unit close to the azo group has been synthesised and studied. The length of the n-alkyl carboxylate chain has been systematically varied in order to establish the effect of the molecular structure on the self-assembling behaviour. Two series of materials possessing hexyl and dodecyl alkyl chains in the chiral part of the molecule have been studied. It has been shown that the length of both the alkyl chains strongly influences the mesomorphic behaviour, however, each chiral/achiral chain has different utility to tune the mesomorphic properties. With exception of the compound with the longest chains, all studied compounds exhibited the chiral tilted ferroelectric smectic C* phase. Based on the combination of terminal alkyl chains, chiral nematic, orthogonal smectic A*, and twist grain boundary smectic A* phases have been detected on cooling beyond the SmC* phase. The presence of the photosensitive functional N=N group in the molecular core allowed further tuning of the material properties by UV light illumination. The E-to-Z photoisomerization of the azo group and subsequent thermal back-isomerisation have been studied in solution by nuclear magnetic resonance and most importantly in the mesophases on bulk samples. We report on UV-induced isothermal switching from chiral smectic and nematic mesophases directly into the isotropic phase, respectively, and differences in the textures of mesophase upon restoration of the ordered liquid.
关键词： E-Z isomerisation,ferroelectric phase,photosensitive liquid crystals,azo group,chiral liquid crystals,NMR spectroscopy,optical switches
更新于2025-09-09 09:28:46
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Structure and Properties of Gallium-Rich Sodium Germano-Gallate Glasses
摘要： Glass compositions in the gallium-rich region of the ternary GaO3/2-GeO2-NaO1/2 vitreous system are studied as a function of the Na/Ga cationic ratio (ranging from 1.30 to 1.61) for a fixed GeO2 content. Glass structures are investigated by 71Ga MAS-NMR, infrared and Raman spectroscopies, and the thermal, optical and physical properties are characterized. Vibrational spectra are interpreted with the help of density functional theory (DFT) calculations. Gallium oxide generally enters the germania network in four-fold coordination, however for Na/Ga ratio below unity, gallium cations tend to charge balance with the formation of 5- or 6-fold coordination units. When the amount of sodium is greater than gallium, non-bridging oxygens (NBOs) are formed preferably on germanate tetrahedral units. These structural descriptions are used to understand the evolution of glass properties such as glass transition temperature, density and refractive index.
关键词： germano-gallate glasses,infrared,vibrational spectroscopy,glass structure,71Ga NMR spectroscopy
更新于2025-09-04 15:30:14
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Aurophilicity and Photoluminescence of (6-Diphenylpnictogenoacenaphth-5-yl)gold Compounds
摘要： The organotin precursors 6-Br-Ace-5-SnBu3 (6, Ace = acenaphthyl) and 6-Ph2E-Ace-5-SnBu3 (7a: E = P; 7b: E = As; 7c: E = Sb) were prepared and used for the synthesis of organogold complexes, namely, the homodinuclear arylgold(I) species (6-Ph2E-Ace-5-Au)2 (8a: E = P; 8b: E = As; 8c: E = Sb), arylgold(III) dichloride 6-Ph2P-Ace-5-AuCl2 (9), diarylgold(III) chloride [trans-(6-Ph2P-Ace-5-)2Au]Cl ([10]Cl) as well as the heterodinuclear gold complexes 6-Ph2P(AuX)-Ace-5-Au(AsPh3) (11a: X = Cl; 11b: X = Br). Compounds 8a - 8c, 11a, and 11b show significant aurophilic interactions, which are related to their photoluminescence upon exposure to UV light. In the solid state, 11a and 11b show green-yellow emission, whereas 8a - 8c are non-emissive. In solution under an argon atmosphere, all five compounds 8a - 8c as well as 11a and 11b show green-yellow emission. The organogold complexes were characterized by multinuclear NMR spectroscopy, photoluminescence spectroscopy, single-crystal X-ray crystallography as well as (TD-)DFT calculations including real-space bond indicators derived from atoms-in-molecules (AIM), the electron localization indicator (ELI-D), and the non-covalent interaction (NCI) index.
关键词： DFT calculations,aurophilicity,photoluminescence,X-ray crystallography,NMR spectroscopy,organogold complexes
更新于2025-09-04 15:30:14
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Phosphorus and Silicon Containing Inorganic Polymers. Poly(dimethylsilane H-phosphonate): Synthesis and NMR Characterization
摘要： In this paper we have demonstrated a new synthetic approach to a phosphorus and silicon containing inorganic polymer with a chain structure [-O-P(O)(H)-O-Si(CH3)2-]. It has been obtained from dichlorodimethylsilane and dimethyl ester of H-phosphonic acid taken in excess via catalyst and solvent free process, performed in two stages. The first one involved dealkylation reaction which was favoured by the nucleophilic attack of the chlorine atoms from the silane derivative at the α–carbon atoms of the dialkyl H-phosphonate. At the second polycondensation stage the molecular mass of the product increased. In the present study dimethyl H-phosphonate and dichlorodimethylsilane were used at a molar ratio 1.3:1 and the process was carried out at temperature up to 65 °C. The structure of the new polymer was proved by multinuclear NMR spectroscopy in solution and solid state. The thermal properties of the polymer product were measured.
关键词： silanes,inorganic polymers,NMR spectroscopy,copolymerization,phosphonates
更新于2025-09-04 15:30:14