Photochromism and Photomagnetism in Two Ni(II) Complexes Based on a Photoactive 2,4,6-Tris-2-Pyridyl-1,3,5-Triazine Ligand.

It is still challenging to construct novel photochromic and photomagnetic materials in the field of molecular materials. Herein, the 2,4,6-tris-2-pyridyl-1,3,5-triazine (TPTz) molecule was found to display photochromic properties under room temperature light irradiation. Two mononuclear structures, [Ni(H2O)(TPTz)(C2O4)]·2H2O (1; C2O42- = oxalate) [Ni(H2O)(TPTz)(C2O4)]·0.5H2O (2), and one chain compound [Ni(TPTz)(H2-HEDP)]·2H2O (3; HEDP = hydroxyethylidene diphosphonate) were obtained by assembling TPTz with polydentate O-ligands (oxalate and phosphonate) and the paramagnetic Ni2+ ions. The electron-transfer (ET)-dominated photochromism was observable in 1 and 2 after light irradiation with the photogeneration of relatively stable radicals, and the resultant photochromism was demonstrated via UV-vis, photoluminescence, X-ray photoelectron spectra, electron paramagnetic resonance spectra, and molecular orbital calculations. Due to the denser stacking interactions between the adjacent organic molecules, 2 exhibited a faster photochromic rate than 1. Compared with 1 and 2, compound 3 did not show photochromic behavior, which was deciphered by the theoretical calculations for all of the compounds. Importantly, the magnetic couplings appeared between photogenerated radicals and paramagnetic Ni2+ ions, resulting in a scarcely photomagnetic phenomenon of 1 and 2 in the Ni-based electron transfer photochromic materials. This work enriches the available kind of ligands for the design of ET photochromic materials, putting forward a method to tune the electron transfer photochromic efficiency in the molecular materials.

miR2118 Negatively Regulates Bacterial Blight Resistance through Targeting Several Disease Resistance Genes in Rice.

Plant miRNAs are a class of noncoding RNA with a length of 21-24 nt that play an important role in plant responses to biotic and abiotic stresses. Bacterial blight (BB) caused by Xanthomonas oryzae pv. oryzae (Xoo) is one of the most serious bacterial diseases in rice. Our previous work showed that osa-miR2118b/n was induced by Xoo infection. However, the biological function of miR2118 has not yet been characterized in experiments. Herein, we constructed MIR2118b OE, as well as single and double mutants of MIR2118b/n using CRISPR/Cas9. Further results showed that osa-MIR2118b OE plants exhibited longer lesion lengths than the wild type after Xoo inoculation, while MIR2118 CRISPR plants exhibited shorter lesion lengths than the wild type after Xoo inoculation. Co-transformation experiments in rice protoplasts indicated that osa-miR2118 negatively regulated the transcripts of three nucleotide-binding sites and leucine-rich repeat (NLR) genes (LOC_Os08g42700.1, LOC_Os01g05600.1, and LOC_Os12g37290.1) which are predicted target genes of miR2118, but not the mutated NLR genes with a 3 bp insertion at the center of the binding sites. The transcriptional level of the three NLR genes was reversed relative to osa-miR2118 in the MIR2118b OE and MIR2118b CRISPR plants. The above results demonstrate that osa-miR2118b/n negatively regulates the resistance to bacterial blight through negatively regulating several NLR genes.

Ultrathin Two-Dimensional Polyoxometalate-Based Metal-Organic Framework Nanosheets for Efficient Electrocatalytic Hydrogen Evolution.

The rational design of 2D polyoxometalate-based metal-organic framework (POMOF) nanosheets on a conductive substrate as a self-supporting electrode is highly attractive but a great challenge. Herein is the first demonstration of POMOF nanopillar arrays consisting of 2D nanosheets as a self-supported electrode for the hydrogen evolution reaction (HER) in acidic conditions. Single-crystal X-ray analysis reveal that our as-prepared 2D [Co2(TIB)2(PMo12O40)]·Cl·4H2O [named CoMo-POMOF; TIB = 1,3,5-tris(1-imidazoly)benzene] crystalline materials are connected by Co-α-Keggin polymolybdate units act as secondary building blocks and TIB as the organic ligands. The 2D CoMo-POMOF nanosheets were successfully arrayed on a conductive nickel foam substrate by a facile CoO nanorod template-assisted strategy. Remarkably, the CoMo-POMOF nanopillar arrays demonstrate superior electrocatalytic performance toward the HER with an overpotential of 137 mV and Tafel slope of 59 mV dec-1 at 10 mA cm-2, which are comparable to those of state-of-the-art POMOF-based electrocatalysts. Density-functional theory (DFT) calculations demonstrate that the exposed bridging oxygen active sites (Oa) of Co-α-Keggin polymolybdate units in CoMo-POMOF optimize the Gibbs free energy of H* adsorption (ΔGH* = -0.11 eV) and increase the intrinsic HER activity.

Large Room Temperature Magnetization Enhancement in a Copper-Based Photoactive Metal-Organic Framework.

The tris(pyridin-4-yl)amine ligand was found to exhibit a radical-actuated coloration phenomenon, and a novel copper-based color-changeable metal-organic framework (MOF) was synthesized via this photoactive ligand. After light irradiation, the photogenerated stable radicals in this framework induced increasing amplitude of magnetization (32%) at room temperature, being the largest enhancement among radical-based photochromic systems.

Photoactive Anthracene-9,10-dicarboxylic Acid for Tuning of Photochromism in the Cd/Zn Coordination Polymers.

Electron transfer photochromic materials with photo-triggered radicals have received huge interest from chemists due to their potentialities in anticounterfeiting, displays, energy conversion, and information storage. However, utilizing the sole carboxylic acid to synthesize novel electron transfer photochromic species is still confronted with huge challenges. Herein, an acentric three-dimensional network Cd2(ADC)2(DMF)2(H2O) (1; ADC = anthracene-9,10-dicarboxylate; DMF = N,N-dimethylformamide) and a two-dimensional layer Zn(ADC)(H2O)·DMA·H2O (2; DMA = N,N-dimethylacetamide) were synthesized and characterized via a photoactive H2ADC ligand. Both compounds exhibited electron transfer photochromism with the formation of radical photoproducts at the solid state, which was revealed by IR, UV-Vis absorption, photoluminescence and electron spin resonance spectra, and magnetic susceptibility measurements. Density functional theory calculations for 1 showed that the coloration process is a metal-assisted ligand-to-ligand electron transfer process between adjacent ADC molecules, and photogenerated stable radicals are delocalized over the ADC components. Compared with 1, the shorter distances between ADC components via coordination bonds promoted 2 to exhibit a higher coloration efficiency and larger quantity of photogenerated radicals. Furthermore, both compounds showed unexpected radical-actuated photochromism in aqueous solution. This work showed that the carboxylic acid ligands, without viologen acceptors, could construct the electron transfer photochromic complexes, showing a novel kind of ligand for the design of hybrid photochromic materials.

Achieving large thermal hysteresis in an anthracene-based manganese(II) complex via photo-induced electron transfer.

Achieving magnetic bistability with large thermal hysteresis is still a formidable challenge in material science. Here we synthesize a series of isostructural chain complexes using 9,10-anthracene dicarboxylic acid as a photoactive component. The electron transfer photochromic Mn2+ and Zn2+ compounds with photogenerated diradicals are confirmed by structures, optical spectra, magnetic analyses, and density functional theory calculations. For the Mn2+ analog, light irradiation changes the spin topology from a single Mn2+ ion to a radical-Mn2+ single chain, further inducing magnetic bistability with a remarkably wide thermal hysteresis of 177 K. Structural analysis of light irradiated crystals at 300 and 50 K reveals that the rotation of the anthracene rings changes the Mn1-O2-C8 angle and coordination geometries of the Mn2+ center, resulting in magnetic bistability with this wide thermal hysteresis. This work provides a strategy for constructing molecular magnets with large thermal hysteresis via electron transfer photochromism.

Enhanced electrochemical properties of potassium-doped lithium-rich oxide@carbon as cathode material for lithium-ion batteries.

Lithium-rich layered oxides are believed to be the most competitive cathode materials for next-generation lithium-ion batteries (LIBs) due to their high specific capacity, but the poor cycle stability and voltage attenuation severely limit their commercial applications. In this paper, a simple method combining surface treatment via pyrolysis of polyvinyl alcohol (PVA) and potassium ions (K+) doping, is designed to improve the above defects of the cobalt-free Lithium-rich material Li1.2Mn0.6Ni0.2O2 (LMR). The insoluble surface byproduct Li2CO3 and amorphous carbon nanolayer derived from the pyrolysis process of PVA alleviate the corrosion of acidic species with a favorable conductivity, while a large radius of K+ can enlarge the space of the lithium (Li) layer to facilitate the diffusion of Li+, suppress voltage polarization, and synchronously restrain the transformation from a layered structure to a spinel-like structure. After modification, the LMR material exhibits a great initial discharge capacity of 266.0 mAh g-1 at 0.1C, a remarkable rate capability of 159.1 mAh g-1 at 5C and an extremely high capacity retention of 98.5% over 200 cycles at 0.5C with a small voltage drop.

Electrospinning Highly Dispersed Ru Nanoparticle-Embedded Carbon Nanofibers Boost CO2 Reduction in a H2/CO2 Fuel Cell.

A H2/CO2 fuel cell is a promising device that can convert CO2 into hydrocarbon fuel with electricity generation. Herein, a facile electrospinning method has been used to synthesize the embedded Ru-CNF catalyst in which Ru nanoparticles are dispersed homogeneously within N-doped carbon nanofibers. This catalyst exhibits a high CH4 production rate of 308.46 µmol gcat-1 h-1 at 170 °C, which is superior to that of the Ru/CNF (242.53 µmol gcat-1 h-1) and Ru/CNT (194.24 µmol gcat-1 h-1). The enhanced CO2RR performance of Ru-CNF is ascribed to the well-distributed Ru nanoparticles within the CNF matrix and synergistic effect of Ru sites with N species, which results in forming the increased CO2RR active sites, hence improving the catalytic activity. Simultaneously, it can achieve a peak power density of 1.8 W m-2 on the strength of anodic (H2 oxidation) and cathodic (CO2 reduction and H2 evolution) reactions with remarkable stability. Such findings give a theoretical basis of CO2RR in the H2/CO2 fuel cell system, which could hold great value to further develop the high-efficiency catalysts for CO2 reduction.

Light actuated stable radicals of the 9-anthracene carboxylic acid for designing new photochromic complexes.

The photogeneration of stable radicals is important but still challenging in the field of optical switching, displays, and other devices. Herein, crystalline 9-anthracene carboxylic acid (9-AC) and a mononuclear complex constructed from this ligand were for the first time discovered to show radical-induced photochromism and photomagnetism after Xe lamp light irradiation. This study finds a simple radical-actuated photochromic molecule for constructing a novel system of photochromic materials.

Quadruple Photoresponsive Functionality in a Crystalline Hybrid Material: Photochromism, Photomodulated Fluorescence, Magnetism and Nonlinear Optical Properties.

As promising photoresponsive materials and potential smart materials, hybrid photochromic materials (HPMs), especially for crystalline HPMs (CHPMs), have been broadly explored for their potential in inheriting the merits of each constituents, and intriguing photomodulated functionality. Hitherto, the photoresponsive functionality in explored CHPMs mainly concentrate on dyad combination. By contrast, triple or quadruple photoresponsive properties are very rare because of the limited compatibility of multiple photoresponsive functionality in a single system. In this work, the electron-transfer (ET) and crystal engineering strategies were utilized to predesign CHPMs with multiple photoresponsive properties via the collaboration of paramagnetic metal ion (Dy3+ ), electron-donor (ED) ligand (benzene-1,2,3-tricarboxylic acid, H3 BTA) and electron-acceptor (EA) ligand (1,10-phenanthroline, phen). The resulting complex [Dy(BTA)(phen)2 ]⋅2H2 O (1) shows hybrid chain with the intrachain Dy3+ ions bridged and chelated by tricarboxylate and phen ligands, respectively. After photostimuli, the ET between tricarboxylate and phen results in photogenerated radicals and the resultant quadruple photoresponsive properties. Considering the abundant resources of paramagnetic metal ions, ED- and EA-ligands, this work provides a general method to construct CHPMs with multiple photoresponsive performances via the collaboration of each unit under the guidance of ET and crystal engineering strategies.

Asymmetric Coordination Toward a Photoinduced Single-Chain Magnet Showing High Coercivity Values.

The production of photo-switchable molecular nanomagnets with substantial coercivity, which is indispensable for information storage and process applications, is challenging. Introducing photo-responsive spin-crossover units provides a feasible means of controlling the magnetic anisotropy, interactions, and overall nanomagnet properties. Herein, we report a cyanide-bridged chain 1⋅12H2 O ({[(Pz Tp)FeIII (CN)3 ]2 FeII (Pmat)2 }n ⋅12 H2 O) generated by linking the FeII -based spin-crossover unit with the [(Pz Tp)Fe(CN)3 ]- (Pz Tp: tetrakis(pyrazolyl)borate) building block in the presence of asymmetric ditopic ligand Pmat ((4-pyridine-4-yl)methyleneamino-1,2,4-triazole). Structural characterization revealed that the introduction of this asymmetric ligand led to a distorted coordination environment of FeII ions, which were equatorially coordinated by four cyanide N atoms, and apically coordinated by one pyridine N atom and one triazole N atom. Upon 808-nm light irradiation, 1⋅12H2 O underwent photoinduced spin-crossover and exhibited single-chain magnet behavior with a coercive field of up to 1.3 T. This represents a 3d-based photoinduced single-chain magnet exhibiting pronounced hysteresis.

Two Photochromic Complexes Assembled by a Nonphotochromic Ligand: Photogenerated Radical Enhanced Room-Temperature Phosphorescence.

Stimulating tunable room-temperature phosphorescence (RTP) is still a challenge in photochromic systems, which is vital for multifunctional coordination materials. Herein, we synthesized two new photochromic chain complexes through self-assembly of the nonphotochromic 1,3,5-tris(4-pyridyl)benzene ligand, diphosphonate, and Ln(III) ions (1 for Ln(III) = Dy and 2 for Ln(III) = Gd). Both compounds showed fast photoresponses with the color turning from yellow to dark gray with a reversible decoloration by heating or storage in the dark. The electron transfer photochromic behavior with the generated stable radicals was further confirmed by the room-temperature UV-vis and electron paramagnetic resonance spectra. Furthermore, via tuning the generation and disappearance of stable radicals, reversible room-temperature fluorescence and phosphorescence for both compounds were switched by light irradiation and a thermal treatment, with an enhanced intensity for RTP and a decrease in fluorescence during the duration of Xe-lamp light irradiation. This work provides a new strategy that photogenerated radicals could promote and enhance RTP properties in functional materials.

Optimizing the Proton Conductivity of Fe-Diphosphonates by Increasing the Relative Number of Protons and Carrier Densities.

Proton conductive materials have attracted extensive interest in recent years due to their fascinating applications in sensors, batteries, and proton exchange membrane fuel cells. Herein, two Fe-diphosphonate chains (H4-BAPEN)0.5·[FeIII(H-HEDP)(HEDP)0.5(H2O)] (1) and (H4-TETA)2·[FeIII2FeII(H-HEDP)2(HEDP)2(OH)2]·2H2O (2) (HEDP = 1-hydroxyethylidenediphosphonate, BAPEN = 1,2-bis(3-aminopropylamino)ethane, and TETA = triethylenetetramine) with different templating agents were prepared by hydrothermal reactions. The valence states of the Fe centers were demonstrated by 57Fe Mössbauer spectra at 100 K, with a high-spin FeIII state for 1 and mixed high-spin FeIII/FeII states for 2. Their magnetic properties were determined, which featured strong antiferromagnetic couplings in the chain. Importantly, the proton conductivity of both compounds at 100% relative humidity was explored at different temperatures, with 2.79 × 10-4 S cm-1 at 80 °C for 1 and 7.55 × 10-4 S cm-1 at 45 °C for 2, respectively. This work provides an opportunity for improving proton conductive properties by increasing the relative number of protons and the carrier density using protonated flexible aliphatic amines.

Manipulating On/Off Single-Molecule Magnet Behavior in a Dy(III)-Based Photochromic Complex.

Exploitation of room temperature (RT) photochromism and photomagnetism to induce single-molecule magnet (SMM) behavior has potential applications toward optical switches and magnetic memories, and remains a tremendous challenge in the development of new bulk magnets. Herein, a series of chain complexes [Ln3(H-HEDP)3(H2-HEDP)3]·2H3-TPT·H4-HEDP·10H2O (QDU-1; Ln = Dy (QDU-1(Dy)), Gd (QDU-1(Gd)), and Y (QDU-1(Y)); HEDP = hydroxyethylidene diphosphonate; TPT = 2,4,6-tri(4-pyridyl)-1,3,5-triazine) were synthesized by solvothermal reactions. All the compounds exhibited reversible photochromic and photomagnetic behaviors via UV light irradiation at RT, induced by the photogenerated radicals via a photoinduced electron transfer (PET) mechanism. More importantly, the PET process induced significant variations in magnetic interactions for the Dy(III) congener. Strong ferromagnetic coupling with remarkably slow magnetic relaxation without applied dc fields was observed between DyIII ions and photogenerated O• radicals, showing SMM behavior after RT illumination. For the first time, we observed the reversible RT photochromism and photomagnetism in the lanthanide-based materials. This work realized the radicals-actuated on/off SMM behavior via RT light irradiation, providing a new strategy for constructing the light-induced SMMs.

Photochromism and photomagnetism in crystalline hybrid materials actuated by nonphotochromic units.

Two novel photochromic and photomagnetic complexes actuated by nonphotochromic ligands have been hydrothermally synthesized through the pillar-layer strategy. After Xe lamp irradiation at room temperature, compound 1 shows naked-eye detectable photochromism, while 2 exhibits an efficient photodemagnetization effect.

A Material Showing Colossal Positive and Negative Volumetric Thermal Expansion with Hysteretic Magnetic Transition.

It is an ongoing challenge to design and synthesize magnetic materials that undergo colossal thermal expansion and that possess potential applications as microscale or nanoscale actuators with magnetic functionality. A paramagnetic metallocyanate building block was used to construct a cyanide-bridged Fe-Co complex featuring both positive and negative colossal volumetric thermal-expansion behavior. A detailed study revealed that metal-to-metal charge transfer between 180 and 240 K induced a volumetric thermal expansion coefficient of 1498 MK-1 accompanied with hysteretic spin transition. Rotation of the magnetic building blocks induced change of π⋅⋅⋅π interactions, resulting in a negative volume expansion coefficient of -489 MK-1 , and another hysteretic magnetic transition between 300 and 350 K. This work presents a strategy for incorporating both colossal positive and negative volumetric thermal expansion with shape and magnetic memory effects in a material.

A Series of Linear {FeIII2 FeII } Complexes with Paramagnetic Building-Block-Modified Spin Crossover Behaviors.

Tuning of the spin crossover (SCO) behavior through paramagnetic building blocks with different steric hindrance effects is of great interest in terms of the synergy between SCO and magnetic interactions. Herein, the steric effect of specified FeIII building blocks is modified, from the large Tp* (hydridotris(3,5-dimethylpyrazol-1-yl)borate) analogue to a small Tp (hydrotris(pyrazolyl)borate) derivative; the FeII SCO unit and FeIII paramagnetic ions are incorporated into three well isolated trinuclear complexes featuring thermally induced and light-induced SCO properties. Reanalysis of the structures reveals that π-π stacking interactions play a key role in the thermal hysteresis and anomalous octahedral distortion parameter Σ around the FeII ion. The Tp* ligand showing the largest steric hindrance induces elongated FeII -N bond lengths and bending of the C≡N-FeII angle in 1, as well as having a relatively large electron donor effect, which leads to the lowest thermal transition temperature among the three compounds.

Light-Induced Bidirectional Metal-to-Metal Charge Transfer in a Linear Fe2 Co Complex.

It is a challenge to reversibly switch both magnetism and polarity using light irradiation. Herein we report a linear Fe2 Co complex, whereby interconversion between FeIIILS (µ-CN)CoIIHS (µ-NC)FeIIILS (LS=low-spin, HS=high-spin) and FeIIILS (µ-CN)CoIIILS (µ-NC)FeIILS linkages could be achieved upon heating and cooling, or alternating laser irradiation at 808 and 532 nm. The electron spin arrangement and charge distribution were simultaneously tuned accompanying bidirectional metal-to-metal charge transfer, providing switchable polarity and magnetism in the complex.

Electrocatalytic water oxidation by a macrocyclic Cu(ii) complex in neutral phosphate buffer.

A single-site copper complex, [Cu(TMC)(H2O)](NO3)2 (1, TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane), was found to be the most active copper-based catalyst towards electrocatalytic water oxidation in neutral aqueous solution. Complex 1 leads to a cathodic shift of approximately 200 mV in potential to reach a current density of 1 mA cm(-2) in comparison with that of the previously reported dinuclear copper complex under the same conditions. Upon immobilization of complex 1 on carbon cloth, it shows greatly improved activity than other copper-based WOCs including CuOx and Cu(2+).

WO3 nanotubes prepared by a coaxial electrospinning method.

In this paper, WO3 nanotubes were prepared by a coaxial electrospinning method. Firstly, core-shell structured composite fibers were fabricated via coaxial electrospinning under the optimal electro-spinning parameters to get the best composite fibers with uniform diameters and smooth surface, which pure PVA being the core solution and PVA/AMT/alcohol being the shell one, respectively. Secondly, the composite fibers were calcined in air at 600 °C for 4 h to wipe out the pure PVA, leading to the formation of nanotubes. After sintering, the obtained WO3 nanotubes were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM). The XRD show that the resultant materials consist of pure tungsten trioxide (WO3) with good crystallinity, while FESEM and HRTEM images indicate that the materials are nanotubes with rough surface and consist of nanoparticles. The inner diameter and the wall thickness of nanotubes were calculated to be around 100 and 50 nm, respectively.