Light-Initiated Imprinted Membrane-Based Biomimetic SERS Sensor toward Selective Detection of Trace MC-LR.

Microcystin-LR (MC-LR) is a severe threat to human and animal health; thus, monitoring it in the environment is essential, especially in water quality protections. Herein, in this work, we synthesize PVDF/CNT/Ag molecular imprinted membranes (PCA-MIMs) via an innovative combination of surface-enhanced Raman spectroscopy (SERS) detection, membrane separation, and molecular-imprinted technique toward the analysis of MC-LR in water. In particular, a light-initiated imprint is employed to protect the chemical structure of the MC-LR molecules. Furthermore, in order to ensure the detection sensitivity, the SERS substrates are combined with the membrane via the assistance of magnetism. The effect of synthesis conditions on the SERS sensitivity was investigated in detail. It is demonstrated from the characteristic results that the PCA-MIMs present high sensitivity to the MC-LR molecules with excellent selectivity against the interfere molecules. Results clearly show that the as-prepared PCA-MIMs hold great potential applications to detect trace MC-LR for the protection of water quality.

Tuning Iron Active Sites of FeOOH via Al3+ and Heteroatom Doping-Induced Asymmetric Oxygen Vacancy Electronic Structure for Efficient Alkaline Water Splitting.

Oxygen evolution reaction is the essential anodic reaction for water splitting. Designing tunable electronic structures to overcome its slow kinetics is an effective strategy. Herein, the molecular ammonium iron sulfate dodecahydrate is employed as the precursor to synthesize the C, N, S triatomic co-doped Fe(Al)OOH on Ni foam (C,N,S-Fe(Al)OOH-NF) with asymmetric electronic structure. Both in situ oxygen vacancies and their special electronic configuration enable the electron transfer between the d-p orbitals and get the increase of OER activity. Density functional theory calculation further indicates the effect of electronic structure on catalytic activity and stability at the oxygen vacancies. In alkaline solution, the catalyst C,N,S-Fe(Al)OOH-NF shows good catalytic activity and stability for water splitting. For OER, the overpotential of 10 mA cm-2 is 264 mV, the tafel slope is 46.4 mV dec-1, the HER overpotential of 10 mA cm-2 is 188 mV, the tafel slope is 59.3 mV dec-1. The stability of the catalyst can maintain ≈100 h. This work has extraordinary implications for understanding the mechanistic relationship between electronic structure and catalytic activity for designing friendly metal (oxy)hydroxide catalysts.

Organoboron Polymorphs with Different Molecular Packing Modes for Optical Waveguides.

Organoboron compounds offer a new strategy to design optoelectronic materials with high fluorescence efficiency. In this paper, the organoboron compound B-BNBP with double B←N bridged bipyridine bearing four fluorine atoms as core unit is facilely synthesized and exhibits a narrowband emission spectrum and a high photoluminescence quantum yield (PLQY) of 86.53% in solution. Its polymorphic crystals were controllable prepared by different solution self-assembly methods. Two microcrystals possess different molecular packing modes, one-dimensional microstrips (1D-MSs) for H-aggregation and two-dimensional microdisks (2D-MDs) for J-aggregation, owing to abundant intermolecular interactions of four fluorine atoms sticking out conjugated plane. Their structure-property relationships were investigated by crystallographic analysis and theoretical calculation. Strong emission spectra with the full width at half maximum (FWHM) of less than 30 nm can also be observed in thin film and 2D-MDs. 1D-MSs possess thermally activated delayed fluorescence (TADF) property and exhibit superior optical waveguide performance with an optical loss of 0.061 dB/µm. This work enriches the diversity of polymorphic microcrystals and further reveals the structure-property relationship in organoboron micro/nano-crystals.

Two High-Nuclear Wheel-Hub-Shaped Transition-Metal-Doped Polyoxovanadates.

The first two unprecedented high-nuclear wheel-hub-shaped transition-metal-doped polyoxovanadates, [M8Mo4W4V20P20] [M = Ni (1), Co (2)], have been assembled under solvothermal conditions. The center of the cluster consists of two {Ni4(oa)4} rings as the center hole, four {MoO4} units acting as the spokes, and four {WV5(PPOA)5} molecular building blocks serving as the tire. Compound 1 exhibits good catalytic properties and recyclability in oxidative desulfurization reactions.

Theoretical Study and Design for Thermally Activated Delayed Fluorescence Emitters with Through-Space Charge Transfer from an Acridine Derivative Donor to an O-Bridged Triphenylboron Boroxy Acceptor.

The through-space charge transfer thermally activated delayed fluorescence (TSCT-TADF) properties of a series of molecules were characterized and tested theoretically by density functional theory and time-dependent density functional theory. By analyzing the weak interaction of the molecules at the ground state and calculating the transition contribution ratio of the donor, acceptor, and bridge in the excited state, we verified the through-space charge transfer characteristic of these molecules. We designed new molecules on the basis of the reported molecules (non-TADF molecule 1 and TADF molecule 2) to improve the performance. Smaller singlet-triplet energy gaps and larger spin-orbit coupling were obtained in the designed molecules, which is beneficial to obtain higher intersystem crossing and reverse intersystem crossing rates (kRISC). In addition, we calculated the radiation rate and the singlet-triplet reorganization energy, which is used to characterize the nonradiation rate. The comprehensive evaluation of both radiative and nonradiative processes shows that molecules 4 and 6 have the potential to be highly efficient TSCT-TADF materials.

Preparation of a Nanosheeted Uranyl-Organic Framework for Enhanced Photocatalytic Oxidation of Toluene.

Preparation of ultrathin metal-organic framework (MOF) nanosheets is an effective way to improve the catalytic efficiency of MOF photocatalysts owing to their superiority in reducing the recombination rate of photogenerated electrons and holes and enhancing charge transfer. Herein, a light-sensitive two-dimensional uranyl-organic framework named HNU-68 was synthesized. Due to its interlayer stacking structure, the corresponding ultrathin nanosheets with a thickness of 4.4 nm (HNU-68-N) can be obtained through ultrasonic exfoliation. HNU-68-N exhibited an enhanced ability to selectively oxidize toluene to benzaldehyde, with the value of turnover frequency being approximately three times higher than that of the bulk HNU-68. This enhancement is attributed to the smaller size and interface resistance of the layered HNU-68-N nanosheets, which facilitate more thorough substrate contact and faster charge transfer, leading to an improvement in the photocatalytic efficiency. This work provides a potential candidate for the application of ultrathin uranyl-based nanosheets.

Insight into the Mechanism of CO2 Chemical Fixation into Epoxides by Windmill-Shaped Polyoxovanadate and n-Bu4NX (X = Br, I).

Carbon dioxide (CO2) coupled with epoxide to generate cyclic carbonate stands out in carbon neutrality due to its 100% atom utilization. In this work, the mechanism of CO2 cycloaddition with propylene oxide (PO) cocatalyzed by windmill-shaped polyoxovanadate, [(C2N2H8)4(CH3O)4VIV4VV4O16]·4CH3OH (V8-1), and n-Bu4NX (X = Br, I) was thoroughly investigated using density functional theory (DFT) calculations. The ring-opening, CO2-insertion, and ring-closing steps of the process were extensively studied. Our work emphasizes the synergistic effect between V8-1 and n-Bu4NX (X = Br, I). Through the analysis of an independent gradient model based on Hirshfeld partition (IGMH), it was found that the attack of n-Bu4NX (X = Br, I) on Cß of PO triggers a distinct attractive interaction between the active fragment and the surrounding framework, serving as the primary driving force for the ring opening of PO. Furthermore, the effect of different cocatalysts was explored, with n-Bu4NI being more favorable than n-Bu4NBr. Moreover, the role of V8-1 in the CO2 cycloaddition reaction was clarified as not only acting as Lewis acid active sites but also serving as "electron sponges". This work is expected to advance the development of novel catalysts for organic carbonate formation.

Fluorescent Sensors Based on Lanthanide-Based Metal-Organic Frameworks via Devices and pH Response.

In light of the escalating industrial and environmental pollution, there is a pressing need for the development of novel materials capable of swiftly detecting pollutants. Here, we report the synthesis of five lanthanide metal-organic frameworks sharing a common structure, prepared via a hydrothermal method and denoted as [Ln2(H2DHBDC)2(phen)(H2O)6]n (where CUST-888 corresponds to Tb, CUST-889 corresponds to Eu, CUST-890 corresponds to Gd, CUST-891 corresponds to Dy, and CUST-892 corresponds to Nd). Notably, CUST-888 and CUST-889 exhibit discernible visual alterations in response to acidic and alkaline conditions. To assess their practical utility, luminescent test strips and light-emitting diode lights based on CUST-888 and CUST-889 were devised, enabling the visual detection of luminescence color changes induced by Hg2+, Cr2O72-, tetracycline, and 2,4,6-trinitrophenol. Furthermore, highlighters derived from CUST-888 and CUST-889 were designed, showcasing robust stability, adjustable color, and substantial potential for application in the realm of anticounterfeiting.

Room-Temperature Synthesis of Covalently Bridged MOP@TpPa-CH3 Composite Photocatalysts for Artificial Photosynthesis.

The conversion of CO2 into useful chemicals via photocatalysts is a promising strategy for resolving the environmental problems caused by the addition of CO2. Herein, a series of composite photocatalysts MOP@TpPa-CH3 based on MOP-NH2 and TpPa-CH3 through covalent bridging have been prepared via a facile room-temperature evaporation method and employed for photocatalytic CO2 reduction. The photocatalytic performances of MOP@TpPa-CH3 are greater than those of TpPa-CH3 and MOP-NH2, where the CO generation rate of MOP@TpPa-CH3 under 10% CO2 still reaches 119.25 µmol g-1 h-1, which is 2.18 times higher than that under pure CO2 (54.74 µmol g-1 h-1). To investigate the structural factors affecting the photocatalytic activity, MOP@TBPa-CH3 without C═O groups is synthesized, and the photoreduction performance is also evaluated. The controlling experimental results demonstrate that the excellent photoreduction CO2 performance of MOP@TpPa-CH3 in a 10% CO2 atmosphere is due to the presence of C═O groups in TpPa-CH3. This work offers a new design and construction strategy for novel MOP@COF composites.

Garnet Structure-Activated Warm White Light Phosphors Ca3Al2Ge3O12: Dy3+, Eu3+ with Ultrahigh Thermal Stability and Tunable Luminescence.

A series of Ca3Al2Ge3O12: xDy3+, yEu3+ phosphors were successfully prepared by the high-temperature solid-phase method. The phase and morphology of the phosphors were studied by means of Rietveld refinement and scanning electron microscopy. The results show that the phase is pure, and the crystal structure is the Ia3̅d space group. In the Ca3Al2Ge3O12: xDy3+ phosphors, using 380 nm excitation, phosphors showed blue (4F9/2 → 6H15/2) and yellow (4F9/2 → 6H13/2) emission peaks at 481 and 581 nm, respectively. In Ca3Al2Ge3O12: xDy3+, yEu3+ phosphors, the energy transfer was inferred by the spectrum overlap of Dy3+ and Eu3+, and the lifetime attenuation was analyzed from the perspective of dynamics; finally, the band gap structure of the phosphors was analyzed by combining diffuse reflection spectra with the first principle, and the energy transfer mechanism and luminescence mechanism were elaborated by combining theory and practice. The transition from blue white light to red light can be achieved by tuning the range of y in Ca3Al2Ge3O12: 0.015Dy3+, yEu3+. Wherein, when y = 0.07, phosphors, the chromaticity coordinate of warm white CIE is (0.3932, 0.3203), the color temperature is 3093 K, and the warm white light is synthesized. The thermal stability of the synthesized warm white phosphors is 90.1% (423 K), the thermal sensing factors are Samax = 5.51 × 10-4 K-1 (303 K) and Srmax = 0.0359% K-1 (303 K), and the actual quantum efficiency is IQE = 52.48%. These results prove that Ca3Al2Ge3O12: Dy3+, Eu3+ have good application prospects as single-component warm w-LED devices.

Tuning optical properties of π-conjugated double nanohoops under external electric field stimuli-responsiveness.

Carbon nanorings have attracted substantial interest from synthetic chemists due to their unique topological structures and distinct physical properties. An intriguing π-conjugated double-nanoring structure, denoted as [8]CPP-[10]cyclacene, was constructed via the integration of [8]cycloparaphenylene ([8]CPP) into [10]cyclacene. Using the external electric field stimuli-responsiveness of [8]CPP-[10]cyclacene, directional charge transfer can be induced, resulting in the emergence of intriguing properties. The effects of the external electric field in three specific directions were explored, vertically in the [8]CPP unit (Fy), vertically in the [10]cyclacene unit (Fz), and horizontally along the double nanorings diameter (Fx). Interestingly, the external electric field vertically to the [10]cyclacene unit significantly enhanced the first hyperpolarizability (ßtot) compared to that vertically to the [8]CPP unit. Notably, [8]CPP-[10]cyclacene under Fx exhibited significantly larger the ßtot values (1.48 × 105 a.u.) than those of vertical Fy and Fz. This work opens up a wide range of nonlinear optics, making it a compelling area to explore in the field of carbon nanomaterials.

A novel single-phase color tunable LiYGeO4:Dy3+, Eu3+ phosphor exhibiting warm white light and excellent thermal stability.

LiYGeO4 phosphors doped with Dy3+ and Eu3+ ions were synthesized using the solid phase method, and their color characteristics were adjustable. The bandgap value of LiYGeO4 calculated by diffuse reflection data is very close to the theoretical value of 3.669 eV, indicating that LiYGeO4 is an ideal candidate for doped rare earth activated ions. The analysis of the emission spectra and fluorescence attenuation curves of Dy3+ and Eu3+ co-doped LiYGeO4 phosphors revealed a clear energy transfer process: energy transfer from Dy3+ to Eu3+. Analysis of emission spectra and fluorescence attenuation curves revealed a transfer of energy from Dy3+ to Eu3+. This transfer mechanism is attributed to the dipole-dipole interactions. In addition, by constantly adjusting the doping levels of Dy3+ and Eu3+, a warm white phosphor with a color temperature of 3881 K was obtained. Finally, the emission intensity of the LiYGeO4:0.015Dy3+,0.02Eu3+ phosphor at 423 K was 86%, indicating that the phosphor has excellent thermal stability and 40% internal quantum efficiency, which proves the potential application of the LiYGeO4 phosphor in white light-emitting diodes (w-LEDs).

Piezofluorochromism in Hierarchical Porous π-stacked Supermolecular Spring Frameworks from Aromatic Chiral Cages.

Piezochromic materials that exhibit pressure-dependent luminescence variations are attracting interest with wide potential applications in mechanical sensors, anticounterfeiting and storage devices. Crystalline porous materials (CPMs) have been widely studied in piezochromism for highly tunable luminescence. Nevertheless, reversible and high-contrast emission response with a wide pressure range is still challenging. Herein, the first example of hierarchical porous cage-based πOF (Cage-πOF-1) with spring structure was synthesized by using aromatic chiral cages as building blocks. Its elastic properties evaluated based on the bulk modulus (9.5 GPa) is softer than most reported CPMs and the collapse point (20.0 GPa) significantly exceeds ever reported CPMs. As smart materials, Cage-πOF-1 displays linear pressure-dependent emission and achieves a high-contrast emission difference up to 154 nm. Pressure-responsive limit is up to 16 GPa, outperforming the CPMs reported so far. Dedicated experiments and density functional theory (DFT) calculations illustrate that π-π interactions-dominated controllable structural shrinkage and porous-spring-structure-mediated elasticity is responsible for the outstanding piezofluorochromism.

Efficient Proton Conductor Based on Bismuth Oxide Clusters and Polyoxometalates.

Developing new solid-state electrolyte materials for improving the proton conductivity remains an important challenge. Herein, a novel two-dimensional layered solid-state proton conductor Bi2O2-SiW12 nanocomposite, based on silicotungstic acid (H4SiW12O40) and Bi(NO3)3·5H2O, was synthesized and characterized. The composite consists of a layered cation framework [Bi2O2]2+ and interlayer-embedded counteranionic [SiW12O40]4-, which forms continuous hydrogen bond (O-H···O) networks through the interaction of adjacent oxygen atoms on the surface of the [Bi2O2]2+ and oxygen atoms of the H4SiW12O40. Facile proton transfer along these pathways endows the Bi2O2-SiW12 (30:1) nanocomposite with an excellent proton conductivity of 3.61 mS cm-1 at 90 °C and 95% relative humidity, indicating that the nanocomposite has good prospects as a highly efficient proton conductor.

Theoretical Insight on the High Reactivity of Reductive Elimination of NiIII Based on Energy- and Electron-Transfer Mechanisms.

Iridium/nickel (Ir/Ni) metallaphotoredox dual catalysis overcomes the challenging reductive elimination (RE) of Ni(II) species and has made a breakthrough progress to construct a wide range of C-X (X = C, N, S, and P) bonds. However, the corresponding reaction mechanisms are still ambiguous and controversial because the systematic research on the nature of this synergistic catalysis is not sufficient. Herein, IrIII/NiII and IrIII/Ni0 metallaphotoredox catalysis have been theoretically explored taking the aryl esterification reaction of benzoic acid and aryl bromide as an example by a combination of density functional theory (DFT), molecular dynamics, and time-dependent DFT computations. It is found that an electron-transfer mechanism is applicable to IrIII/NiII metallaphotoredox catalysis, but an energy-transfer mechanism is applicable to IrIII/Ni0 combination. The IrIII/NiII metallaphotoredox catalysis succeeds to construct a NiI-NiIII catalytic cycle to avoid the challenging RE of Ni(II) species, while the RE occurs from triplet excited-state Ni(II) species in the IrIII/Ni0 metallaphotoredox catalysis. In addition, the lower lowest unoccupied molecular orbital energy level of Ni(III) species than that of Ni(II) species accelerates RE from Ni(III) one. The triplet excited-state Ni(II) species can resemble a Ni(III) center, considering the metal-to-ligand charge transfer character to promote the RE.

Endohedral Functionalization for Structural Transformation of Polyoxovanadate-Based Metal-Organic Cube.

Functionalized internal modifications of metal-organic polyhedra (MOPs) can endow properties and functions different from the original ones. Until now, there have been only a few examples of endohedral modifications of polyoxovanadate-based MOPs. Herein, an efficient coordination-driven strategy was chosen for the inner modification of two metal-organic cubes (MOCs) with different sizes, VMOC-1 and VMOC-4, constructed from polyoxovanadate clusters [V6O6(OCH3)9(SO4)(CO2)3]2- SBU and tetradentate ligands. Pyridinophosphonic acid with potential coordination capability was introduced to replace the sulfate of the hexavanadate cluster and graft the pyridine functional group inside the cage. The introduction of pyridylphosphate in the VMOC-4 system gave a cubic cage with a pyridyl endo-modified isomer. Interestingly, the smaller cubic cage VMOC-1 was induced to undergo structural transformation to obtain VMOC-py-1. The organic dyes adsorption of VMOC-py-1 and VMOC-1 showed that the endomodified structure could adsorb larger and more dyes, compared to the original cube.

Defect Healing of Micro/Nanocrystals via the Coordination Competition of Rare Earth in Crystal Engineering.

Defect engineering has been generally observed and utilized in crystal materials including metal oxides, metal-organic frameworks, and so on; however, how to relate the defect formation and crystallization process is needed to be revealed clearly, and how to heal the defect is a big challenge. Herein, based on the new coordination complex (HNU-53), the crystal defects were created by increasing the reaction time and crystal size. Following the crystal growth process, the crystal color centers were simultaneously generated, resulting in fluorescence quenching. To heal the defect, the crystal growth was controlled by the introduction of rare earth ions. With the coordination competition of rare earth ions, the crystal defects were reduced and recovery of fluorescence emission was achieved.

Construction of Zr-Metal-Organic Frameworks-Based Composite Materials toward Anhydrous Proton Conduction and Photocatalytic CO2 Reduction.

Metal-organic frameworks constructed from Zr usually possess excellent chemical and physical stability. Therefore, they have become attractive platforms in various fields. In this work, two families of hybrid materials based on ZrSQU have been designed and synthesized, named Im@ZrSQU and Cu@ZrSQU, respectively. Im@ZrSQU was prepared through the impregnation method and employed for proton conduction. Im@ZrSQU exhibited terrific proton conduction performance in an anhydrous environment, with the highest proton conduction value of 3.6 × 10-2 S cm-1 at 110 °C. In addition, Cu@ZrSQU was synthesized via the photoinduction method for the photoreduction of CO2, which successfully promoted the conversion of CO2 into CO and achieved the CO generation rate of up to 12.4 µmol g-1 h-1. The photocatalytic performance of Cu@ZrSQU is derived from the synergistic effect of Cu NPs and ZrSQU. Based on an in-depth study and discussion toward ZrSQU, we provide a versatile platform with applications in the field of proton conduction and photocatalysis, which will guide researchers in their further studies.

Self-Consistent Quantum Mechanics/Embedded Charge Study on Aggregation-Enhanced Delayed Fluorescence of Cu(I) Complexes: Luminescence Mechanism and Molecular Design Strategy.

To elucidate the luminescence mechanism of highly efficient blue Cu(N^N)(POP)+-type thermally activated delayed fluorescence (TADF) materials, we have selected Cu(pytfmpz)(POP)+ (1) and Cu(pympz)(POP)+ (2) as targets to investigate the photophysical properties in both solution and solid phases. The self-consistent electrostatic potential (ESP) embedded charge within the quantum mechanics/molecular mechanics (QM/MM) method demonstrates a greater advantage over the charge equilibrium (QEQ) in accurately calculating atomic charges and reasonably describing the polarization effect, ultimately resulting in a favorable consistency between simulation and experimental measurements. After systematic and quantitative simulation, it has been found that complex 2, with an electron-donating group of -CH3, exhibits a much more blue-shifted spectrum and a significantly enhanced efficiency in comparison to complex 1 with -CF3. This is due to the widened HOMO-LUMO gap as well as the narrowed energy gap between the lowest singlet and triplet excited states (ΔEST), respectively. Then, the designed complex 3 is introduced with a stronger electron donor and larger tert-butyl group, which plays a key role in simultaneously suppressing the structural distortion and reducing the ΔEST. This leads to a faster reverse intersystem crossing process than that of the two experimental complexes in solution, turning out to be a new deep-blue-emitting material with excellent TADF performance.

Molecular Design of Highly Efficient Heavy-Atom-free NpImidazole Derivatives for Two-Photon Photodynamic Therapy and ClO- Detection.

Two-photon photodynamic therapy (TP-PDT), as a treatment technology with deep penetration and less damage, provides a broad prospect for cancer treatment. Nowadays, the development of TP-PDT suffers from the low two-photon absorption (TPA) intensity and short triplet state lifetime of photosensitizers (PSs) used in TP-PDT. Herein, we propose some novel modification strategies based on the thionated NpImidazole (the combination of naphthalimide and imidazole) derivatives to make efforts on those issues and obtain corresponding fluorescent probes for detecting ClO- and excellent PSs for TP-PDT. Density functional theory (DFT) and time-dependent DFT (TD-DFT) are used to help us characterize the photophysical properties and TP-PDT process of the newly designed compounds. Our results show that the introduction of different electron-donating groups at the position 4 of NpImidazole can effectively improve their TPA and emission properties. Specifically, 3s with a N,N-dimethylamino group has a large triplet state lifetime (τ = 699 µs) and TPA cross section value (δTPA = 314 GM), which can effectively achieve TP-PDT; additionally, 4s (with electron-donating group 2-oxa-6-azaspiro[3.3]heptane in NpImidazole) effectively realizes the dual-function of a PS for TP-PDT (τ = 25,122 µs, δTPA = 351 GM) and a fluorescent probe for detecting ClO- (Φf = 29% of the product 4o). Moreover, an important problem is clarified from a microscopic perspective, that is, why the transition property of 3s and 4s (1π-π*) from S1 to S0 is different from that of 1s and 2s (1n-π*). It is hoped that our work can provides valuable theoretical clues for the design and synthesis of heavy-atom-free NpImidazole-based PSs and fluorescent probes for the detection of hypochlorite.