Nonlinear Optical Effects of Hybrid Antimony(III) Halides Induced by Stereoactive 5s2 Lone Pairs and Trimethylammonium Cations.

Organic-inorganic hybrid metal halides have unique optical and electronic properties, which are advantageous in the study of nonlinear optical materials. To investigate the effect of stereoactive lone pair electrons and the induction of organic cations on the structure of hybrid antimony(III) halides on nonlinear optics, we synthesize two noncentrosymmetric hybrid antimony(III)-based halide single crystals (TMA)3Sb2X9 (TMA = NH(CH3)3+, X = Cl, Br) by a room-temperature slow evaporation method, and their single-crystal structures, phase transition, X-ray photoelectron spectroscopy, and energy-band structure calculations are studied. More importantly, second-harmonic generation results of (TMA)3Sb2X9 (X = Cl, Br) are about 0.7 and 0.8 × KH2PO4(KDP), respectively. Interestingly, (TMA)3Sb2Cl9 single crystals undergo a reversible structural transition from Pc (No. 7) at room temperature to P21/c (No. 14) at 400 K, while the (TMA)3Sb2Br9 single crystals belong to the noncentrosymmetric space group R3c (No. 161), which clarifies the previous results. This work not only deepens the understanding of the role in lone pair electrons and organic cations in the structural induction in antimony-based halide perovskite materials but also provides guidance for subsequent nonlinear optical explorations.

The Effect of Different Substances Embedded in Fullerene Cavity on Surfactant Self-Assembly Behavior through Molecular Dynamics Simulation.

Fullerene-based amphiphiles are new types of monomers that form self-assemblies with profound applications. The conical fullerene amphiphiles (CFAs) have attracted attention for their uniquely self-assembled structures and have opened up a new field for amphiphile research. The CFAs and CFAs with different substances embedded in cavities are designed and their self-assembly behaviors are investigated using molecular dynamics (MD) simulations. The surface and internal structures of the micelles are analyzed from various perspectives, including micelle size, shape, and solvent-accessible surface area (SASA). The systems studied are all oblate micelles. In comparison, embedding Cl- or embedding Na+ in the cavities results in larger micelles and a larger deviation from the spherical shape. Two typical configurations of fullerene surfactant micelles, quadrilateral plane and tetrahedral structure, are presented. The dipole moments of the fullerene molecules are also calculated, and the results show that the embedded negatively charged Cl- leads to a decrease in the polarity of the pure fullerene molecules, while the embedded positively charged Na+ leads to an increase.

Oxidation-Induced Dissolution Recrystallization Structural Transformation Strategy Enhanced Nonlinear Optical Effect of Hybrid Chiral Tin Bromide Single Crystals.

In order to reveal the integrated effect of inorganic lattice structure disturbances and chiral ligands on the structure of tin halide hybrid materials, we show the synthesis, crystal growth, dissolution recrystallization structural transformation (DRST), optical properties, energy band structure, and nonlinear optical properties of a class of chiral tin bromide R/S-2-mpip[SnBr3]Br (2-mpip is 2-methylpiperazinium) and R/S-2-mpipSnBr6 for the first time. The formation of R/S-2-mpipSnBr6 in solution was interestingly caused by irreversible DRST of R/S-2-mpip[SnBr3]Br. The second-harmonic generation response of the new phase R-2-mpipSnBr6 is significantly enhanced compared to that of the initial phase R-2-mpip[SnBr3]Br. These structural transformations of chiral tin bromides reflect, to some extent, the DRST commonality of the tin halide family induced by oxidation and serve as a starting point for investigating the structural chirality and asymmetry of chiral metal hybrid halides.

Thermal/Water-Induced Phase Transformation and Photoluminescence of Hybrid Manganese(II)-Based Chloride Single Crystals.

Mn(II)-based hybrid halides have attracted great attention from the optoelectronic fields due to their nontoxicity, special luminescent properties, and structural diversity. Here, two novel organic-inorganic hybrid Mn(II)-based halide single crystals (1-mpip)MnCl4·3H2O and (1-mpip)2MnCl6 (1-mpip = 1-methylpiperazinium, C5H14N2+) were grown by a slow evaporation method in ambient atmosphere. Interestingly, (1-mpip)2MnCl6 single crystals exhibit the green emission with a PL peak at 522 nm and photoluminescence quantum yields (PLQYs) of ≈5.4%, whereas (1-mpip)MnCl4·3H2O single crystals exhibit no emission characteristics. More importantly, there exists a thermal-induced phase transformation from (1-mpip)MnCl4·3H2O to emissive (1-mpip)2MnCl6 at 372 K. Moreover, a reversible luminescent conversion between (1-mpip)MnCl4·3H2O and (1-mpip)2MnCl6 was simply achieved when heated to 383 K and placed in a humid environment or sprayed with water. This work not only deepens the understanding of the thermal-induced phase transformation and humidity-sensitive luminescent conversion of hybrid Mn(II)-based halides, but also provides a guidance for thermal and humidity sensing and anticounterfeiting applications of these hybrid materials.

Molecular Dynamics Simulations on the Adsorbed Monolayers of N-Dodecyl Betaine at the Air-Water Interface.

Betaine is a kind of zwitterionic surfactant with both positive and negative charge groups on the polar head, showing good surface activity and aggregation behaviors. The interfacial adsorption, structures and properties of n-dodecyl betaine (NDB) at different surface coverages at the air-water interface are studied through molecular dynamics (MD) simulations. Interactions between the polar heads and water molecules, the distribution of water molecules around polar heads, the tilt angle of the NDB molecule, polar head and tail chain with respect to the surface normal, the conformations and lengths of the tail chain, and the interfacial thickness of the NDB monolayer are analyzed. The change of surface coverage hardly affects the locations and spatial distributions of the water molecules around the polar heads. As more NDB molecules are adsorbed at the air-water interface, the number of hydrogen bonds between polar heads and water molecules slightly decreases, while the lifetimes of hydrogen bonds become larger. With the increase in surface coverage, less gauche defects along the alkyl chain and longer NDB chain are obtained. The thickness of the NDB monolayer also increases. At large surface coverages, tilted angles of the polar head, tail chain and whole NDB molecule show little change with the increase in surface area. Surface coverages can change the tendency of polar heads and the tail chain for the surface normal.

Molecular Dynamics Study on the Aggregation Behavior of Triton X Micelles with Different PEO Chain Lengths in Aqueous Solution.

The aggregation structure of Triton X (TX) amphiphilic molecules in aqueous solution plays an important role in determining the various properties and applications of surfactant solutions. In this paper, the properties of micelles formed by TX-5, TX-114, and TX-100 molecules with different poly(ethylene oxide) (PEO) chain lengths in TX series of nonionic surfactants were studied via molecular dynamics (MD) simulation. The structural characteristics of three micelles were analyzed at the molecular level, including the shape and size of micelles, the solvent accessible surface area, the radial distribution function, the micelle configuration, and the hydration numbers. With the increase of PEO chain length, the micelle size and solvent accessible surface area also increase. The distribution probability of the polar head oxygen atoms on the surface of the TX-100 micelle is higher than that in the TX-5 or TX-114 micelle. In particular, the tail quaternary carbon atoms in the hydrophobic region are mainly located at the micelle exterior. For TX-5, TX-114, and TX-100 micelles, the interactions between micelles and water molecules are also quite different. These structures and comparisons at the molecular level contribute to the further understanding of the aggregation and applications of TX series surfactants.

The charge-transfer states and excitation energy transfers of halogen-free organic molecules from first-principles many-body Green's function theory.

The organic solar cells based on halogen-free components, have been the new favorites to develop green and renewable energy. PBDB-T and its derivatives are considered the superior electron donors to construct the solar cells. Although there are plenty of researches about them, the charge-transfer mechanisms and excitation energy transfers of relative organic solar cells are still unclear, the developments of photovoltaic devices are restricted consequently. In this work, we calculate the electronic structures and excited-state properties of PBDB-T, PBT1-C, PBT1-O and PBT1-S donors in the gas phase from the many-body Green's function theory. With BTP-IC and BTP-IS as the acceptors, we consider the Förster, Dexter, and overlap electronic couplings to compute the excitation energy transfers of the dimers. The ionization energies and excited-state energies of the four donors calculated by GW + BSE are in good agreement with experiments, and they are sensitive to the functionals in the computation. We find two charge transfer schemes. The thienyl of PBDB-T molecule makes its charge-transfer state at the lowest energy, and the total electronic coupling of PBDB-T based dimer is the strongest. The Dexter, and overlap types electronic couplings are significant to study the excitation energy transfer of organic heterojunctions. We provide a theoretical guide in the design and synthesis of higher-performance halogen-free donors.

Organic-Inorganic Hybrid Tin Halide Single Crystals with Sulfhydryl and Hydroxyl Groups: Formation, Optical Properties, and Stability.

Lead (Pb)-free halide hybrid materials have received a great deal of attention because of their potential in optoelectronic applications. However, heteroatom-based amine lead-free tin halide hybrid single crystals have not been well investigated yet. Detailed synthetic processes, growth, crystal structures, and stability of (ACH2CH2NH3)2SnBr6 (A = OH or SH) and (BCH2CH2NH3)2SnI4 (B = I or SH) single crystals were investigated. Interestingly, (IH3NCH2CH2SSCH2CH2NH3)2HPO3 exhibited orange-red photoluminescence (PL) at about 620 nm with an average PL lifetime of about 912 ns. (HSCH2CH2NH3)2SnI4 single crystals exhibited a PL peak at 620 nm with an average PL lifetime of about 0.607 ns. More importantly, (HSCH2CH2NH3)2SnI4 single crystals exhibited reversible red-black color transformations when exposed to a H3PO2 solution and an ambient atmosphere, which was attributed to oxidation from Sn2+ to Sn4+, rather than from I- to I3- (I2). The intriguing characteristics should provide guidance for further optoelectronic applications of these Pb-free halide hybrid materials.

Chiral Hybrid Copper(I) Iodide Single Crystals Enable Highly Selective Ultraviolet-Pumped Circularly Polarized Luminescence Applications.

Light-emitting diodes (LEDs) with the circularly polarized luminescence features have attracted attention to the promising applications ranging from solid-state lighting and displays to bioencoding and anticounterfeiting. The prerequisite of circularly polarized luminescence is highly emissive chiral materials. Here, we demonstrated that (R/S-MBA)4Cu4I8·2H2O (MBA = α-methylbenzylaminium) and acentric Gua6Cu4I10 (Gua = guanidinium) single crystals were grown on the basis of Gua3Cu2I5 by the slow evaporation method. (R/S-MBA)4Cu4I8·2H2O single crystals exhibited excellent circularly polarized luminescence (CPL) characteristics. More importantly, ultraviolet-pumped LEDs (UV-LEDs) based on (R/S-MBA)4Cu4I8·2H2O and Gua6Cu4I10 single crystals exhibit a higher optical selectivity when exposed to right-handed and left-handed circular polarization (RCP and LCP) conditions. (S-MBA)4Cu4I8·2H2O single crystals and Gua6Cu4I10 single crystals induced by the (R)-MBA cation exhibit the different polarized light intensities at PL peak positions in different λ/4 waveplate polarizer angle directions, which provides new possibilities for the further applications from 3D displays to spintronics, as well as anticounterfeiting.

Layered Perovskite (CH3NH3)2Pb(SCN)2I2 Single Crystals: Phase Transition and Moisture Stability.

To study stability issues of three-dimensional perovskites, there is a strategy to introduce the thiocyanate ion (SCN-) into CH3NH3PbI3 (MAPbI3) to solve these problems. Here, we report the bulk growth of layered perovskite MA2Pb(SCN)2I2 single crystals by different growth methods in an ambient atmosphere. We also investigate the structural determination and refinements, band gap, and photoluminescence of MA2Pb(SCN)2I2 single crystals. More importantly, the phase transition and stability of MA2Pb(SCN)2I2 are systematically demonstrated. MA2Pb(SCN)2I2 undergo the reversible single-crystal to single-crystal phase transition in the orthorhombic systems from the space group Pmmn (no. 59) to the space group Pmn21 (no. 31) at low temperature. Moreover, the temperature-dependent recovery behaviors of MA2Pb(SCN)2I2 single crystals, powders, and thin films at high temperature are studied in detail. Besides, the moisture stability of MA2Pb(SCN)2I2 is described when exposed to moisture condition by the experiment and theoretical calculations. It would be interesting to not only conduct a comprehensive study on the crystal structures and the phase transition processes of layered perovskites but also provide guidance for further optoelectronic applications of these perovskite materials.

Molecular dynamics simulations on fullerene surfactants with different charges at the air-water interface.

The interfacial activity of fullerene surfactants at the air-water interface is studied via molecular dynamics and metadynamics simulations. Fullerene surfactants with different charges show different surface activity. Meanwhile, studies show that fullerene surfactants with zero or one positive charge show interesting interface behaviour, i.e. the hydrophobic fullerene of the fullerene surfactant with zero charge orients to bulk water while the fullerene surfactant with one positive charge can be a hydrophilic and hydrophobic rotator at the air-water interface.

Mediating both valence and conduction bands of TiO2 by anionic dopants for visible- and infrared-light photocatalysis.

Doping is an effective way to extend the optical absorption of TiO2 to the visible range. Doping of TiO2 by carbon has been found to enhance the water splitting efficiency significantly in experiment. However, the mechanism behind this is elusive. Using the ab initio many-body Green's function theory, we find that the C2 dimer formed on the TiO2 surface produces a shallow delocalized occupied Ti 3d state just below the bottom of the conduction bands. Therefore, band-gap narrowing in carbon-doped TiO2 is caused by the opposite shifts of both valence and conduction bands simultaneously, which is in contrast to the generally accepted idea that anionic dopants can only affect the valence band of TiO2. Optical absorption in the infrared region is also increased compared to reduced TiO2. The spatially well-separated photogenerated electrons and holes might help to reduce the recombination rate of carriers, in favor of improvement in photocatalysis efficiency. This novel behavior of anionic dopants is distinct from previous understandings and may guide the engineering of TiO2.

A molecular dynamics study of cellulose inclusion complexes in NaOH/urea aqueous solution.

We investigated the dissolution state of cellulose in NaOH/urea aqueous solution using molecular dynamics simulations. All the components, including cellulose, NaOH, urea and H2O were combined into one simulation. A clear and detailed description for the formation of cellulose inclusion complexes has been stated. The simulation results showed that the cellulose inclusion complexes exhibited anisotropic properties. In this system, the sodium ions and hydroxide ions located at the regions of hydroxyl and hydroxymethyl groups in cellulose molecules. However, the urea molecules occupied the faces of the hydrophobic pyranose rings. The hydrogen-bonding configuration and lifetime of hydrogen bonds in cellulose inclusion complexes were also systematically characterized. The spatial structure of inclusion complexes, the hydrogen-bonding interaction between cellulose and solvent molecules, the diffusive property of solvent molecules and the distribution of water-water angles in cellulose inclusion complexes were discussed in details. The NaOH, urea and H2O molecules surrounding the cellulose chain within radial distance 0.35 nm have smaller diffusion coefficients than those in bulk state. The water-water angles provide a quantitative estimate of hydrophobic effect of cellulose.

Self-assembly of water-soluble silver nanoclusters: superstructure formation and morphological evolution.

Supramolecular self-assembly, based on non-covalent interactions, has been employed as an efficient approach to obtain various functional materials from nanometer-sized building blocks, in particular, [Ag6(mna)6]6-, mna = mercaptonicotinate (Ag6-NC). A challenging issue is how to modulate the self-assembly process through regulating the relationship between building blocks and solvents. Herein, we report the controlled self-assembly of hexanuclear silver nanoclusters into robust multilayer vesicles in different solvents, DMSO, CH3CN, EG and MeOH. Their unique luminescence enables them to be bifunctional probes to sense Fe3+ and dl-dithiothreitol (DTT). By protonating the Ag6-NC to Ag6-H-NC using hydrochloric acid (HCl), the multilayer vesicles survive in aprotic solvents, DMSO and CH3CN, but are transformed to nanowires in protic solvents, water, EG and MeOH. Our results demonstrated that the solvent-bridged H-bond plays a key role in the evolution of the morphologies from vesicles to nanowires. Moreover, the nanowires could further hierarchically self-assemble in water into hydrogels with high water content (99.5%), and with remarkable mechanical strength and self-healing properties. This study introduces a robust cluster-based building block in a supramolecular self-assembly system and reveals the significance of aprotic and protic solvents for the modulation of the morphologies of cluster-based aggregates.

Highly Sensitive Detection of Ionizing Radiations by a Photoluminescent Uranyl Organic Framework.

Precise detection of low-dose X- and γ-radiations remains a challenge and is particularly important for studying biological effects under low-dose ionizing radiation, safety control in medical radiation treatment, survey of environmental radiation background, and monitoring cosmic radiations. We report here a photoluminescent uranium organic framework, whose photoluminescence intensity can be accurately correlated with the exposure dose of X- or γ-radiations. This allows for precise and instant detection of ionizing radiations down to the level of 10-4  Gy, representing a significant improvement on the detection limit of approximately two orders of magnitude, compared to other chemical dosimeters reported up to now. The electron paramagnetic resonance analysis suggests that with the exposure to radiations, the carbonyl double bonds break affording oxo-radicals that can be stabilized within the conjugated uranium oxalate-carboxylate sheet. This gives rise to a substantially enhanced equatorial bonding of the uranyl(VI) ions as elucidated by the single-crystal structure of the γ-ray irradiated material, and subsequently leads to a very effective photoluminescence quenching through phonon-assisted relaxation. The quenched sample can be easily recovered by heating, enabling recycled detection for multiple runs.

Electronic structures of rutile (011)(2 × 1) surfaces: A many-body perturbation theory study.

Using the GW method within many-body perturbation theory, we investigate the electronic properties of the rutile (011) surfaces with different reconstruction patterns. We find that keeping the Ti:O ratio on the reconstructedsurface to 1:2 enlarges the bandgap of the rutile (011) surface to ca. 4.0 eV. Increasing the content of O atoms in the surface can turn rutile into a semi-metal. For some surfaces, it is important to apply self-consistent GW calculation to get the correct charge distributions for the frontier orbitals, which are relevant to the photocatalytic behavior of TiO2.

Investigation of Transport Properties of Water-Methanol Solution through a CNT with Oscillating Electric Field.

Molecular dynamics simulations were used to investigate the transport properties of water-methanol solution getting through a carbon nanotube (CNT) with an oscillating electric field. Eight alternating electric fields with different oscillation periods were used in this work. Under the oscillating electric field, water molecules have the advantage of occupying a CNT over methanol molecules. Meanwhile, the space occupancy of water-methanol solution in the CNT increases as the oscillating period increases. More importantly, we found that the oscillating period of electric field affects the van der Waals interaction of the solution inside the CNT and the shell of the CNT, which results in the change in the number of hydrogen bonds in the water-methanol solution confined in the CNT. And the change in the hydrogen-bond network leads to the change in transport properties of water-methanol solution.

Influence of functional groups on water splitting in carbon nanodot and graphitic carbon nitride composites: a theoretical mechanism study.

The coupling of carbon nanodots (C-Dots) with graphitic carbon nitride (g-C3N4) has been demonstrated to boost the overall photocatalytic solar water splitting efficiency. However, the understanding on the role of the C-Dots and how the structure of C-Dots influences the photocatalytic reaction is still limited. In this work, we investigate the excited states of some C-Dot/g-C3N4 composites with the C-Dots containing different functional groups including -OH, -CHO and -COOH by first-principles many-body Green's function theory. It is found that the increase of efficiency can be ascribed to the high separation rate and the low recombination rate of the electron-hole pair benefiting from the emergence of the charge-transfer excited state between the C-Dots and g-C3N4. Functional groups on the C-Dots play a crucial role in determining the charge transfer direction, active sites for reduction reaction and oxidation reaction of water, and whether the reaction is a four-electron process or a two-electron/two-electron process. These results can provide guidance for the design and optimization of the C-Dots for heterojunction photocatalysts.

Tunable Yellow-Red Photoluminescence and Persistent Afterglow in Phosphors Ca4LaO(BO3)3:Eu3+ and Ca4EuO(BO3)3.

In most Eu3+ activated phosphors, only red luminescence from the 5D0 is obtainable, and efficiency is limited by concentration quenching. Herein we report a new phosphor of Ca4LaO(BO3)3:Eu3+ (CLBO:Eu) with advanced photoluminescence properties. The yellow luminescence emitted from the 5D1,2 states is not thermally quenched at room temperature. The relative intensities of the yellow and red emission bands depend strongly on the Eu3+ doping concentration. More importantly, concentration quenching of Eu3+ photoluminescence is absent in this phosphor, and the stoichiometric compound of Ca4EuO(BO3)3 emits stronger luminescence than the Eu3+ doped compounds of CLBO:Eu; it is three times stronger than that of a commercial red phosphor of Y2O3:Eu3+. Another beneficial phenomenon is that ligand-to-metal charge transfer (CT) transitions occur in the long UV region with the lowest charge transfer band (CTB) stretched down to about 3.67 eV (∼330 nm). The CT transitions significantly enhance Eu3+ excitation, and thus result in stronger photoluminescence and promote trapping of excitons for persistent afterglow emission. Along with structure characterization, optical spectra and luminescence dynamics measured under various conditions as a function of Eu3+ doping, temperature, and excitation wavelength are analyzed for a fundamental understanding of electronic interactions and for potential applications.

Characterization of berkelium(III) dipicolinate and borate compounds in solution and the solid state.

Berkelium is positioned at a crucial location in the actinide series between the inherently stable half-filled 5f(7) configuration of curium and the abrupt transition in chemical behavior created by the onset of a metastable divalent state that starts at californium. However, the mere 320-day half-life of berkelium's only available isotope, (249)Bk, has hindered in-depth studies of the element's coordination chemistry. Herein, we report the synthesis and detailed solid-state and solution-phase characterization of a berkelium coordination complex, Bk(III)tris(dipicolinate), as well as a chemically distinct Bk(III) borate material for comparison. We demonstrate that berkelium's complexation is analogous to that of californium. However, from a range of spectroscopic techniques and quantum mechanical calculations, it is clear that spin-orbit coupling contributes significantly to berkelium's multiconfigurational ground state.