Regulating Planarized Intramolecular Charge Transfer for Efficient Single-Phase White-Light Emission in Undoped Metal-Organic Framework Nanocrystals.

The technology of combining multiple emission centers to exploit white-light-emitting (WLE) materials by taking advantage of porous metal-organic frameworks (MOFs) is mature, but preparing undoped WLE MOFs remains a challenge. Herein, a pressure-treated strategy is reported to achieve efficient white photoluminescence (PL) in undoped [Zn(Tdc)(py)]n nanocrystals (NCs) at ambient conditions, where the Commission International del'Eclairage coordinates and color temperature reach (0.31, 0.37) and 6560 K, respectively. The initial [Zn(Tdc)(py)]n NCs exhibit weak-blue PL consisting of localized excited (LE) and planarized intramolecular charge transfer (PLICT) states. After pressure treatment, the emission contributions of LE and PLICT states are balanced by increasing the planarization of subunits, thereby producing white PL. Meanwhile, the reduction of nonradiative decay triggered by the planarized structure results in 5-fold PL enhancement. Phosphor-converted light-emitting diodes based on pressure-treated samples show favorable white-light characteristics. The finding provides a new platform for the development of undoped WLE MOFs.

Regulating Second Coordination Shell of Ce Atom Site and Reshaping of Carrier Enable Single-Atom Nanozyme to Efficiently Express Oxidase-like Activity.

Single-atom nanozymes (SANs) are considered to be ideal substitutes for natural enzymes due to their high atom utilization. This work reported a strategy to manipulate the second coordination shell of the Ce atom and reshape the carbon carrier to improve the oxidase-like activity of SANs. Internally, S atoms were symmetrically embedded into the second coordination layer to form a Ce-N4S2-C structure, which reduced the energy barrier for O2 reduction, promoted the electron transfer from the Ce atom to O atoms, and enhanced the interaction between the d orbital of the Ce atom and p orbital of O atoms. Externally, in situ polymerization of mussel-inspired polydopamine on the precursor helps capture metal sources and protects the 3D structure of the carrier during pyrolysis. On the other hand, polyethylene glycol (PEG) modulated the interface of the material to enhance water dispersion and mass transfer efficiency. As a proof of concept, the constructed PEG@P@Ce-N/S-C was applied to the multimodal assay of butyrylcholinesterase activity.

Superior Superconducting Properties Realized in Quaternary La-Y-Ce Hydrides at Moderate Pressures.

The recent revolution in the superconductivity field stems from hydride superconductors. Multicomponent hydrides provide a crucial platform for tracking high-temperature superconductors. Besides high superconducting transition temperature (Tc), achieving both giant upper critical magnetic field [µ0Hc2(0)] and high critical current density [Jc(0)] is also key to the latent potential of the application for hydride superconductors. In this work, we have successfully synthesized quaternary La-Y-Ce hydrides with excellent properties under moderate pressure by using the concept of "entropy engineering." The obtained temperature dependence of the resistance provides evidence for the superconductivity of Fm3m-(La,Y,Ce)H10, with the maximum Tc ∼ 190 K (at 112 GPa). Notably, Fm3m-(La,Y,Ce)H10 boasts exceptional properties: µ0Hc2(0) reaching 292 T and Jc(0) surpassing 4.61 × 107 A/cm2. Compared with the binary LaH10/YH10, we find that the Fm3m structure in (La,Y,Ce)H10 can be stable at relatively low pressures (112 GPa). These results indicate that multicomponent hydrides can significantly enhance the superconducting properties and regulate stabilizing pressure through the application of "entropy engineering." This work stimulates the experimental exploration of multihydride superconductors and also provides a reference for the search of room-temperature superconductors in more diversified hydride materials in the future.

Isomerization of Covalent Organic Frameworks for Efficiently Activating Molecular Oxygen and Promoting Hydrogen Peroxide Photosynthesis.

Constitutional-isomerized covalent organic frameworks (COFs), constructed by swapping monomers around imine bonds, have attracted attention for their distinct optoelectronic properties, which significantly impact photocatalytic performance. However, limited research has delved into the inherent relationship between isomerization and the enhancement of H2O2 photosynthesis. Herein, a pair of isomeric COFs linked by imine bonds (PB-PT-COF and PT-PB-COF) is synthesized, and it is proved that isomeric COFs exhibit different rate-determining steps in the generation process of H2O2, resulting in a twofold increase in photocatalytic efficiency. Specifically, PT-PB-COF demonstrates effective adsorption and activation of molecular oxygen (O2 + e- → •O2 - + e- → H2O2), leading to a significant improvement in H2O2 photocatalytic efficiency. In contrast, PB-PT-COF exhibits robust interaction with H2O, enabling direct oxidation of H2O (H2O + h+ → H2O2). This study provides a thorough understanding of the intrinsic mechanism underlying the constitutional-isomerized COFs in the photocatalytic H2O2 generation, offering insights for further optimizing building units.

Theory-Guided Experimental Design of Covalent Triazine Frameworks for Efficient Photocatalytic Hydrogen Production.

The high crystalline covalent triazine framework-1 (CTF-1), composed of alternating triazine and phenylene, has emerged as an efficient photocatalyst for solar-driven hydrogen evolution reaction (HER). However, it is of great challenge to further improve photocatalytic HER performance via increasing crystallinity due to its near-perfect crystallization. Herein, an alternative strategy of scaffold functionalization is employed to optimize the energy band structure of crystalline CTF-1 for boosting hydrogen-evolving activity. Guided by the computational predictions, versatile CTF-based polymer photocatalysts are prepared with different functional groups (OH, NH2, COOH) using binary polymerization for practical hydrogen production. Experiment evidence verifies that the introduction of a limited number of electron-donating groups is sufficient to maintain high crystallinity in CTF, modulate the band structure, broaden visible light absorption, and consequently enhance its photophysical properties. Notably, the functionalization with OH exhibits the most positive effect on CTF-1, delivering a photocatalytic activity with a hydrogen-producing rate exceeding 100 µmol h-1.

A Thorough Examination of the Variables Affecting the Quantum Efficiency of Radiative Decay of Trichlorotriphenylmethyl Radicals.

Fluorescence quantum efficiency is determined by the competition between radiation and nonradiation processes of the excited states. Understanding the factors affecting the radiation and nonradiative decay rates is of great significance for the design of luminescent materials. The excitation state deactivation mechanisms of singlet and triplet states have been extensively studied, providing a comprehensive understanding of the processes involved in the relaxation of these states. However, research on free radical systems involving doublet states is relatively scarce. Therefore, in this study, radiation and nonradiative decay rates and the mechanism of a series of trichlorotriphenylmethyl-based radicals were investigated theoretically. The results indicate that the relative rotations of electron donor and acceptor, as well as the internal rotations of trichlorotriphenylmethyl moiety, play important roles in energy dissipation through nonradiative channels. The effect of a solid-state environment on the radiation and nonradiative decay rates of radicals was investigated using a combination of quantum mechanics and molecular mechanics methods. The results indicate that the solid-state environment restricts the expansion of the conjugated system in the excited state of radicals, leading to a slight decrease in radiative decay rate. In addition, the solid-state environment reduces the reorganization energy and also affects the adiabatic excitation energy of radicals. The reduction in reorganization energy results in a decrease in nonradiative rate, while the opposite effect is observed for adiabatic excitation energy. The nonradiative rate of radicals in a solid-state environment is thus inflected by a combination of molecular geometric structure relaxation and ground-excited state energy gap.

Density Functional Calculation and Evaluation of the Spectroscopic Properties and Luminescent Material Application Potential of the N-Heterocyclic Platinum(II) Tetracarbene Complexes.

A series of reported Pt(II) carbene complexes possibly have the ability to serve as the new generation of blue emitters in luminescent devices because of their narrow emission spectra, high photoluminescence quantum yields (PLQYs), and rigid molecular skeleton. However, the combination of all carbene ligands with different multidentate structures will affect the overall planarity and horizontal dipole ratio to varying degrees, but the specific extent of this effect has not previously been analyzed in detail. In this work, density functional computation is used to study a class of platinum tetracarbene bidentate complexes with similar absorption and emission band characteristics, which is the main reason for the remarkable difference in quantum efficiency due to subtle differences in electronic states caused by different ligands. From the calculation results, the major reason, which results in significantly decrease in quantum efficiency for [Pt(cyim)2]2+, is that [Pt(cyim)2]2+ can reach the non-radiative deactivation metal-centered d-d excited state through an easier pathway compared with [Pt(meim)2]2+. The result, based on changes in the dihedral angle between ligands, can achieve the goal of improving and designing materials by adjusting the degree of the dihedral angle. (meim: bis(1,1'-dimethyl-3,3'-methylene-diimidazoline-2,2'-diylidene); cyim: bis(1,1'-dicyclohexyl-3,3'-methylene-diimidazoline-2,2'-diylidene).

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.

Synergistic Integration of Amorphous Cobalt Phosphide with a Conductive Channel for Highly Efficient Electrocatalytic Nitrate Reduction to Ammonia.

Electrocatalytic nitrate reduction to ammonia (NO3 RR) is regarded as a viable alternative reaction to "Haber Bosch" process. Nevertheless, it remains a major challenge to explore economical and efficient electrocatalysts that deliver high NH3 yield rates and Faraday efficiencies (FE). Here, it demonstrates the fabrication of a 3D core-shell structured Co-carbon nanofibers (CNF)/ZIF-CoP for NO3 RR application. Benefitting from the distinct electron transport property of Co-CNF and desirable mass transfer ability from amorphous CoP framework, the as-prepared Co-CNF/ZIF-CoP exhibits large NH3 FE (96.8 ± 3.4% at -0.1 V vs reversible hydrogen electrode (RHE)) and high yield rate (38.44 ± 0.65 mg cm-2 h-1 at -0.6 V vs RHE), which are better than Co-CNF/ZIF-crystal CoP. Density functional theory (DFT) calculations further reveal that amorphous CoP presents a lower energy barrier in the rate determination step of the protonation of *NO to produce *NOH intermediates compared with crystal CoP, resulting in a superior NO3 RR performance. Eventually, an aqueous galvanic Zn-NO3 - battery is assembled by using Co-CNF/ZIF-CoP as cathode material to achieve efficient production of NH3 whilst simultaneously supplying electrical power. This work offers a reliable strategy to construct amorphous metal phosphide framework on conducting CNF as efficient electrocatalyst and enriches its promising application for NO3 RR.

Dynamic Metastable Characteristics of Carbon Cages Embedded with Er2C2.

Novel endohedral metallofullerenes (EMFs), namely, Er2C2@C2v(5)-C80, Er2C2@Cs(6)-C82, Er2C2@Cs(15)-C84, Er2C2@C2v(9)-C86, Er2C2@Cs(15)-C86, and Er2C2@Cs(32)-C88, had been experimentally synthesized, and the unique structures and many fascinating properties had also been widely explored. Nevertheless, the position of the Er atoms inside the cage shows a severe disorder within the stable EMF monomer, which is difficult to understand and explain from the experimental point of view. In this work, based on the density functional theoretical calculations, the Er2C2@Cs(6)-C82 has 73 directional isomers and 2 Er atoms that are far beyond from Er-Er single bonding and tend to be close to the cage side (marked as "shell"), and the core (Er2C2 units) takes on a butterfly shape as generally revealed. The energy difference between any two of the isomers is in the range of 0.05 to 25.6 kcal/mol, indicating a relatively easy thermodynamic transition between the isomers. The other five Er carbide cluster EMFs (Er2C2@C2v(5)-C80, Er2C2@Cs(15)-C84, Er2C2@C2v(9)-C86, Er2C2@Cs(15)-C86, and Er2C2@Cs(32)-C88) are also studied in the same way, and 30, 37, 39, and 43 most stable Er-oriented sites inside the cage, respectively, are obtained. In addition, the shape of the Er2C2 gradually changed from butterfly to linear. Moreover, the electronic structure and molecular orbital analyses show that it is easy for Er2C2@C80-88 to form a charge transfer state of [Er2C2]4+@[C80-88]4- via the dynamic core-shell coordination equilibrium. Er2C2 with a steep drop in chemical stability is restricted to forming varying degrees of metastable states in the shell, determined by the shell size, to ensure the overall stability. The lowest unoccupied molecular orbital energy level of these EMFs is increased by 0.5-1.1 eV compared with fullerenes C80-88, potentially providing favorable conditions for suitable energy level matching with EMF as an electron acceptor used in organic solar cell devices.

Investigating the influence of substituent groups in TTM based radicals for the excitation process: a theoretical study.

Tri-(2,4,6-trichlorophenyl)methyl (TTM) based radicals can be promising in providing relatively high fluorescence quantum efficiency. In this study, we have evaluated the photoluminescence properties of a series of TTM-based radicals by means of DFT and TD-DFT methods. The optimized structures of the ground states (D0) and the first excited states (D1) of all the radicals are calculated and the computed emission bands are comparable with previous experimental results. knr is determined from transition dipole moments (µ12) and the energy gaps between D0 and D1 (ΔE), both of which can be regulated by the conjugated structures from the substituent groups. knr was derived from the mode-averaging method and is consistent with the experimental results. Factors influencing kr and knr, including the potential energy differences (ΔG0), the vibrational reorganization energies (λ) and the electron coupling term (Hab), are discussed. By comparing kr and knr in solvents with different polarities (cyclohexane, toluene, and chloroform), TTM based radicals in cyclohexane exhibit the most promising fluorescence efficiencies. Besides, two substituted radicals, namely 2Br-TTM-3PCz and 2F-TTM-3PCz, have been fabricated. The results show that fluorine atoms are able to increase ΔG0 and a considerably small knr has been predicted. We expect that our calculation can benefit the design of light-emitting molecules in further experiments.

Differences of Atomic-Level Interactions between Midazolam and Two CYP Isoforms 3A4 and 3A5.

CYP 3A4 and CYP 3A5 are two important members of the human cytochrome P450 family. Although their overall structures are similar, the local structures of the active site are different, which directly leads to obvious individual differences in drug metabolic efficacy and toxicity. In this work, midazolam (MDZ) was selected as the probe substrate, and its interaction with two proteins, CYP 3A4 and CYP 3A5, was studied by molecular dynamics simulation (MD) along with the calculation of the binding free energy. The results show that two protein-substrate complexes have some similarities in enzyme-substrate binding; that is, in both complexes, Ser119 forms a high occupancy hydrogen bond with MDZ, which plays a key role in the stability of the interaction between MDZ and the enzymes. However, the complex formed by CYP 3A4 and MDZ is more stable, which may be attributed to the sandwich structure formed by the fluorophenyl group of the substrate with Leu216 and Leu482. Our study interprets the binding differences between two isoform-substrate complexes and reveals a structure-function relationship from the atomic perspective, which is expected to provide a theoretical basis for accurately measuring the effectiveness and toxicity of drugs for individuals in the era of precision medicine.

Constructing High Efficiency CoZnx Mn2-x O4 Electrocatalyst by Regulating the Electronic Structure and Surface Reconstruction.

It is an effective strategy to develop novel electrocatalysts with controllable defects to enhance their electrocatalytic activity and stability. However, how to precisely design these catalysts on the atom scale remains very difficult. Herein, several vacancy-dependent CoZnx Mn2-x O4 catalysts are prepared through tailoring the concentration of Zn ions. The in situ activation of the obtained products accelerates the surface reconstruction. The superior electrocatalytic performance can be ascribed to the formations of MOOH (Mn, Co) active species and abundant oxygen vacancies, which are comparable to noble IrO2 and Pt/C catalysts. Zn-CoMn2 O4 -1.5 catalyst delivers a cell voltage of 1.63 V and long durability. Density functional theory calculations demonstrate that the appropriate Zn ion doping can improve the density states of p electron on the surface of catalysts significantly and benefit the d-band center closing to Fermi level, suggesting their high charge carrier density and low adsorption energy.

Can a molecular switch exist in both superalkali electride and superalkalide forms?

To combine both electride and alkalide characteristics in one molecular switch, it is shown herein that the phenalenyl radical and the M3 ring (M3-PHY, M = Li, Na, and K) stacked with parallel and vertical geometries are good candidates. The former geometry is the superalkali electride e-⋯M3+-PHY while the latter geometry is the superalkalide Mδ--M2(1-δ)+-PHY-. The superalkalide Mδ--M2(1-δ)+-PHY- may isomerize to the superalkali electride e-⋯M3+-PHY (M = Li, Na, and K) using suitable long-wavelength irradiation, while the latter may isomerize to the former with suitable short-wavelength irradiation. Also, applying suitable oriented external electric fields can drive the superalkalide Mδ-M2(1-δ)+-PHY- to change into the superalkali electride e-⋯M3+-PHY (M = Li, Na, and K). The differences in the static and dynamic first hyperpolarizability (ß0) values between them were also studied.

Maximized Green Photoluminescence in Tb-Based Metal-Organic Framework via Pressure-Treated Engineering.

Lanthanide metal-organic frameworks are of great interest in the development of photoluminescence (PL) materials owing to their structural tunability and intrinsic features of lanthanide elements. However, there exists some limitations arising from poor matching with metal ions, thereby exhibiting a weak ligand-to-metal energy transfer (LMET) process. Here we demonstrate a pressure-treated strategy for achieving high PL performance in green-emitting Tb(BTC)(H2 O)6 . The PL quantum yield of pressure-treated sample increased from 50.6 % to 90.4 %. We found that the enhanced hydrogen bonds locked the conjugated configuration formed by two planes of carboxyl group and benzene ring, enabling the promoted intersystem crossing to effectively drive LMET. Moreover, the optimized singlet and triplet states also validated the facilitated LMET process. This work opens the opportunity of structure optimization to improve PL performance in MOFs by pressure-treated engineering.

Computational Studies on the Materials Combining Graphene Quantum Dots and Pt Complexes with Adjustable Luminescence Characteristics.

Graphene materials with particular properties are proved to be beneficial to photoelectric devices, but there are rare reports on a positive effect by graphene on emissive layer materials of organic light-emitting diodes (OLEDs) previously. On the basis of the latest important experiments, an OLED device with the aid of graphene quantum dots shows the dawn of their application for luminescent materials. The luminescence performance has been improved, but the understanding of the internal excited-state radiation mechanism of the material needs further study. In this work, the Pt(II)-coordinated graphene quantum dot coplanar structures with different shapes are studied theoretically in detail, and the results present the improvement in phosphorescence under the promoted radiative decay and suppressed nonradiative decay. This composite combines the advantages of transition metal complexes and graphene quantum dots and also exhibits excellent properties in the light absorption region and carrier transportation for the OLED. This comprehensive theoretical calculation research can provide a comprehensive basis of the material design in the future.

Theoretical study on the molecular stacking interactions and charge transport properties of triazasumanene crystals - from explanation to prediction.

Computational analyses of the solid-state properties of triazasumanene (TAS), a C3-symmetric nitrogen-doped sumanene derivative, were carried out in this work. The present studies are mainly divided into two parts. In the first part, we demonstrated the differences in the interactions of the crystal packing between the racemic and the homochiral structures: the former having perpendicular columnar packing and the latter forming slipped helical packing. Two geometries of the TAS monomer, a theoretically optimized structure under vacuum and an X-ray crystal structure in experiment, were compared. It can be found that it is not the total interaction energy, but the local interactions (mainly the electrostatic interactions) of the molecular dimer that dominate the columnar stacking conformation. The second part involves the investigation of the potential charge transport properties of the crystals according to the semiclassical Marcus theory with the hopping mechanism using the simple dimer model. The charge transfer integrals of the two sets of dimers, racemic and homochiral dimer models, were compared as well. The calculation results show that the TAS racemic crystal was predicted to have an advantage of hole transport properties. The perpendicular columnar stacking of the homochiral conformation should essentially have better charge transport properties than the racemic conformation. It is reasonable to employ the simple dimer model built using optimized monomers under vacuum for the purpose of the prediction of the molecular packing conformation by IES calculation and the charge transport properties of the perpendicular columnar-stacking crystal. Our work provides a simple approach to the deep understanding of the structure-property relationship of bowl-shaped molecular systems in theory. It can help to facilitate the design and preparation of heteroatom-doped sumanene derivatives with perpendicular columnar stacking crystals as novel organic semiconductor materials.

Energy Platform for Directed Charge Transfer in the Cascade Z-Scheme Heterojunction: CO2 Photoreduction without a Cocatalyst.

A universal strategy is developed to construct a cascade Z-Scheme system, in which an effective energy platform is the core to direct charge transfer and separation, blocking the unexpected type-II charge transfer pathway. The dimension-matched (001)TiO2 -g-C3 N4 /BiVO4 nanosheet heterojunction (T-CN/BVNS) is the first such model. The optimized cascade Z-Scheme exhibits ≈19-fold photoactivity improvement for CO2 reduction to CO in the absence of cocatalysts and costly sacrificial agents under visible-light irradiation, compared with BVNS, which is also superior to other reported Z-Scheme systems even with noble metals as mediators. The experimental results and DFT calculations based on van der Waals structural models on the ultrafast timescale reveal that the introduced T as the platform prolongs the lifetimes of spatially separated electrons and holes and does not compromise their reduction and oxidation potentials.

Water-soluble fluorescent probe for simultaneous detection of cyanide, hypochlorite and bisulfite at different emission wavelengths.

A fluorescent probe that responds at distinct wavelengths upon exposure to cyanide, hypochlorite, and bisulfite was synthesized. As a result, an easy to apply analytical methodology was developed for the detection of these ions. The feasibility of this method was evaluated by theoretical calculations. The probe exhibited excellent solubility in the test solution (H2O: DMF = 99: 1, v: v) with low detection limits for cyanide, hypochlorite and bisulfite (4.5 × 10 -8 M, 4.9 × 10 -7 M and 4.3 × 10 -8 M respectively) showing distinct emission wavelengths for each ion without interference in practical application. Furthermore, the probe had low toxicity and was applied for the imaging experiments of cyanide, hypochlorite and bisulfite in living HeLa and MDCK cells.

Stimuli-Responsive Luminescent Properties of Tetraphenylethene-Based Strontium and Cobalt Metal-Organic Frameworks.

Herein we report two new TPE-based 3D MOFs, that is, Sr-ETTB and Co-ETTB (TPE=Tetraphenylethylene, H8 ETTB=4',4''',4''''',4'''''''-(ethene-1,1,2,2-tetrayl)tetrakis(([1,1'-biphenyl]-3,5-dicarboxylic acid))). Through tailoring outer shell electron configurations of SrII and CoII cations, the fluorescence intensity of the MOFs is tuned from high emission to complete non-emission. Sr-ETTB with strong blue fluorescence shows reversible fluorescence variations in response to pressure and temperature, which is directly related to the reversible deformation of the crystal structure. In addition, non-emissive Co-ETTB counterpart exhibits a turn-on fluorescent enhancement under the stimulation of analyte histidine. In the process, TPE-cored linkers in the MOFs are released through competitive coordination substitution and subsequently reassembled to perform aggregation-induced luminescence behavior originated from the organic linkers.