In-depth theoretical analysis of the influence of an external electric field on charge transport parameters.

It is important to develop materials with environmental stability and long device shelf life for use in organic field-effect transistors (OFETs). The microscopic, molecular-level nature of the organic layer in OFETs is not yet well understood. The stability of geometric and electronic structures and the regulation of the external electric field (EEF) on the charge transport properties of four typical homogeneous organic semiconductors (OSCs) were investigated by density functional theory (DFT). The results showed that under the EEF, the structural changes in single-bond linked oligomers were more sensitive and complex than those of condensed molecules, and there were non-monotonic changes in their reorganization energy (λ) during charge transport under an EEF consisting of decreases and then increases (Series D). The change in λ under an EEF can be preliminarily and qualitatively determined by the change in the frontier molecular orbitals (FMOs) - the number of C-atoms with nonbonding characteristics. For single-bonded molecules, the transfer integral is basically unchanged under a low EEF, but it will greatly change at a high EEF. Because the structure and properties of the molecule will greatly change under different EEFs, the effect of an EEF should be fully considered when determining the intrinsic mobility of OSCs, which could cause a deviation 0.3-20 times in mobility. According to detailed calculations, one heterogeneous oligomer, TH-BTz, was designed. Its λ can be greatly reduced under an EEF, and the change in the energy level of FMOs can be adjusted to different degrees. This study provides a reasonable idea for verification of the experimental mobility value and also provides guidance for the directional design of stable high-mobility OSCs.

The cadmium tolerance enhancement through regulating glutathione conferred by vacuolar compartmentalization in Aspergillus sydowii.

Aspergillus was found to be a vital hyperaccumulation species for heavy metal removal with admirable tolerance capacity. But the potential tolerance mechanism has not been completely studied. This study quantified the amounts of total cadmium (Cd), Cd2+, glutathione (GSH), and reactive oxygen species (ROS) in the protoplasts and vacuoles of mycelium. We modulated GSH synthesis using buthionine sulfoximine (BSO) and 2-oxothiazolidine-4-carboxylic acid (OTC) to investigate the subcellular regulatory mechanisms of GSH in the accumulation of Cd. The results confirmed that GSH plays a crucial role in vacuolar compartmentalization under Cd stress. GSH and GSSG as a redox buffer to keep the cellular redox state in balance and GSH as a metal chelating agent to reduce toxicity. When regulating the decreased GSH content with BSO, and increased GSH content with OTC, the system of Cd-GSH-ROS can change accordingly, this also supported that vacuolar compartmentalization is a detoxification strategy that can modulate the transport and storage of substances inside and outside the vacuole reasonably. Interestingly, GSH tended to be distributed in the cytoplasm, the battleground of redox takes place in the cytoplasm but not in the vacuole. These finding potentially has implications for the understanding of tolerance behavior and detoxification mechanisms of cells. In the future bioremediation of Cd in soil, the efficiency of soil remediation can be improved by developing organisms with high GSH production capacity.

Soil organic carbon stability and exogenous nitrogen fertilizer influence the priming effect of paddy soil under long-term exposure to elevated atmospheric CO2.

Soil organic carbon (SOC) stability and dynamics are greatly influenced by long-term elevated atmospheric CO2 [CO2]. The priming effect (PE) is vital in SOC stability and dynamics, but its role in paddy soil under long-term elevated [CO2] remains unclear. To examine how SOC stability changed in paddy soil after long-term elevated atmospheric CO2 enrichment, the PE was quantified through a 13C-glucose-induced experiment with different N levels for topsoil (0-20 cm) from paddy free-air CO2 enrichment (FACE) platform. Compared with the ambient CO2 concentration ([CO2]), 10 years of elevated [CO2] (500 µmol·mol-1) significantly increased SOC and TN content by 18.4% and 19.0%, respectively, while the C/N ratio was not changed. The labile C fractions including dissolved organic carbon (DOC) and readily oxidizable organic carbon (ROC), but excluding microbial biomass C (MBC), accumulated faster than SOC in paddy soil, which implied the reduced SOC stability for long-term elevated [CO2] enrichment. With the decline of SOC stability, the exogenously induced cumulative specific PE (PE per gram of SOC) remarkably increased by 41.1-72.7% for elevated [CO2] fumigation. The cumulative PE, especially the cumulative specific PE, was found significantly linearly correlated with the ROC content or ROC/SOC ratio (labile SOC pool). Furthermore, the application of nitrogen fertilizer slowed down the PE under elevated [CO2] condition. Our results showed that long-term elevated [CO2] enrichment reduced SOC stability and, together with exogenous nitrogen fertilizer, regulated the PE in paddy soil.

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.

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.

Theoretical study of the tuning role of ß-methylthio or ß-methylselenyl on the charge-transport properties of acenedithiophenes derivatives.

To date, the manipulation of intermolecular nonconjugation interactions in organic crystals is still a great challenge due to the complexity of weak intermolecular interactions. Here we designed molecules substituted by ß-methylselenyl on naphtho[1,2-b:5,6-b']dithiophene and anthra[2,3-b:6,7-b']dithiophene, respectively (anti-ß-MS-NDT, anti-ß-MS-ADT), which together with anti-ß-MS-BDT synthesized experimentally all exhibited 2D brickwork π-stacking. Moreover, their maximum molecular carrier mobilities reached 3.30 and 16.46 cm2 V-1 s-1. These results indicated that the substitution of ß-methylselenyl could be a strategy to directionally adjust the parent herringbone stacking into 2D brickwork π-stacking. Hirshfeld surface analysis and symmetry-adapted perturbation theory (SAPT) were used to investigate the nonconjugated interactions in the pitched π-stacking formed by the ß-methylthio-substituted acenedithiophene derivatives and the 2D brickwork π-stacking of the ß-methylselenyl-substituted ones; wherein, the steric hindrance caused by the introduction of the substituents promoted Csp2-Csp2⋯π interactions to replace Csp2-H⋯π to stabilize the face-to-face stacking. Moreover, by calculating the decomposition energy of the intermediate state model of the molecular stacking mode that may exist in the replacement conversion process, it was found that the energy of this intermediate state was larger than that of the actual ones, finally confirming the inevitability of the actual existence in this stacking. In addition, because of the reduction in intensity of the special vibration modes, it could be found that the ß-methylselenyl substitution showed better phonon assistance than ß-methylthio substitution in terms of dynamic disorder. This study is a further step toward fully understanding the relationship between intermolecular interactions and regulation of the molecular stacking.

Photophysical Exploration of Zn(II) Polypyridine Photosensitizers in Two-Photon Photodynamic Therapy: Insights from Theory.

The high incidence and difficulties of treatment of cancer have always been a challenge for mankind. Two-photon photodynamic therapy (TP-PDT) as a less invasive technique provides a new perspective for tumor treatment due to its low-energy near-infrared excitation, high targeting, and minor damage. At present, the emerging metal complexes used as the photosensitizers (PSs) in TP-PDT have aroused great interest. However, most metal complexes as PSs in TP-PDT still face some problems, such as slow clearance, unsatisfactory two-photon absorption (TPA) characteristics, high price, low reactivity, and poor solubility. In this work, density functional theory and time-dependent density functional theory were used to characterize the one/two-photon response, solvation free energy, and lipophilicity of a series of novel PSs applied in TP-PDT. The results suggest that based on complex 1, replacing Ru(II) center with Zn(II) (complex 2) can effectively prolong the triplet excited state lifetime while reducing the cost and environmental pollution, and the azetidine heterospirocycles were introduced into the ligand scaffold (complex 3), which effectively reduced the vibration relaxation of the ligand group and improved the water solubility; further, the addition of acetylenyl groups subtly enhanced the light absorption and significantly improved the two-photon response (complex 4). In addition, all complexes met the requirement of a PS and could be used as potential candidates for TP-PDT. In particular, complex 4 has the advantages of high solvation free energy, a large TPA cross-section (1413 GM), a long triplet state lifetime (671 µs), good chemical reactivity, and low cost, and it is easy to be scavenged by organisms. Overall, this contribution may provide an important clue to formulate clear design principles for type I/II PSs and rational design of PSs with high intersystem crossing rates, a long lifetime, and therapeutic excitation wavelengths.

A Theoretical Investigation into the Homo- and Hetero-leptic Cu(I) Phosphorescent Complexes Bearing 2,9-dimethyl-1,10-phenanthroline and bis [2-(diphenylphosphino)phenyl]ether Ligand.

Cu(I) complexes have received widespread attention as a promising alternative to traditional noble-metal complexes. Herein, we systematically study the properties of Cu(I) complexes from homo- to hetero-ligands, and found the following: (1) hetero-ligands are beneficial to regulate phosphorescent efficiency; (2) when the hetero-ligands in a tetracoordinated Cu(I) complex are 1:1, the ligands coordinate along the dx2-y2 direction of Cu(I) ion, which can observably suppress structural deformation; (3) unlike the P^P ligand, the N^N ligand can enhance the participation of Cu(I) during the transition process; (4) the addition of an appropriate amount of P^P ligand can effectively raise the energy level of HOMO (highest occupied molecular orbital), enhance the proportion of LLCT (ligand-ligand charge transfer), and thereby increase the available singlet emission transition moments which can be borrowed, thus promoting the radiative decay process. As a result, this work provides a detailed understanding of the effects of different ligands in Cu(I) complexes, and provides a valuable reference and theoretical basis for regulating and designing the phosphorescent properties of Cu(I) complexes in the future.

Insight into the Vacuolar Compartmentalization Process and the Effect Glutathione Regulation to This Process in the Hyperaccumulator Plant Solanum nigrum L.

Vacuole compartmentalization plays an important role in the storage of heavy metals in hyperaccumulators. Is the vacuolar compartmentation a simple shielding process or a dynamic process that continuously consumes cell sap resources? How does glutathione affect the process of vacuolar compartmentalization? These unknown questions are very important to understand the mechanism of vacuole compartmentalization and can provide a guide for the design of hyperaccumulator plants by genetic engineering. Therefore, this study explored the enzyme activities, total cadmium, Cd2+, glutathione, oxidized glutathione, and reactive oxygen species contents in protoplasts and vacuoles of leaf cells in Solanum nigrum L. through subcellular separation. The results showed that vacuolar compartmentalization was a dynamic process that actively induced the related substances produced by cell sap to enter the vacuole for detoxification. When regulating the decreased glutathione content with buthionine sulfoximine, the total cadmium and combined cadmium in protoplasm decreased significantly, but the vacuole still maintained a high proportion of cadmium content and stable ROS content, which indicated that various external resources were preferentially used to maintain cadmium storage and homeostasis in vacuole rather than outside vacuole. These findings could guide the use of genetic engineering to design hyperaccumulator plants.

Phytoremediation of cadmium-contaminated soils by Solanum nigrum L. enhanced with biodegradable chelating agents.

The application of biodegradable chelating agents to enhance phytoremediation is a low-cost and promising method to improve the remediation efficiency of heavy metal-contaminated soil. The effects of N, N-bis glutamic acid (GLDA) on the growth and heavy metal absorption of Solanum nigrum were studied by pot experiment. The addition of chelate on the 20th day after sowing can improve the bioavailability of cadmium (Cd) in the soil. The results showed that the addition of chelating agents effectively improved the migration rate of the target heavy metal Cd in the soil, and significantly increased the accumulation of heavy metal in the roots, stems, and leaves of plants. The results showed that compared with the control group, the chelating agent could increase the extraction rate of total Cd by 28.65-68.74%. The application of GLDA significantly increased the accumulation of Cd (20 mg kg-1 and 40 mg kg-1), reaching 24.28-40.30 and 25.71-33.16 µg of pot-1 DW, respectively. At the same time, GLDA increased Cd stress by decreasing plant biomass, inhibiting photosynthetic pigment synthesis and increasing MDA levels. These results indicated that GLDA could improve the absorption of Cd by S. nigrum, which provided a new idea for its practical application in the remediation of Cd-contaminated soil.

CO2 bubble-assisted in-situ construction of mesoporous Co-doped Cu2(OH)2CO3 nanosheets as advanced electrodes towards fast and highly efficient electrochemical reduction of nitrate to N2 in wastewater.

The development of high-efficient and cost-effective electrocatalysts is crucial to remove nitrate pollutant in wastewater. Herein, we design and prepare mesoporous Co-doped Cu2(OH)2CO3 malachite nanosheets as an electrocatalyst toward highly efficient nitrate reduction using a facile CO2 bubble-assisted coprecipitation synthesis. The electrocatalytic performance is subject to the Co/Cu ratio of this malachite. Remarkably, compared with the pristine monometal Cu or Co-based electrocatalyst, the optimal electrocatalyst, 0.3Co@Cu2(OH)2CO3, displays fast and highly efficient removal capacity of nitrate with an impressive high total nitrogen (TN) removal of 8628.99 mg N g-1CoCu (398.79 mg N gcat-1 h-1), N2 selectivity of 97.11% as well as negligible nitrite product at 100 mg L-1 NO3--N and 2000 mg L-1 Cl- neutral electrolyte. Above all, high total nitrogen removal efficiency (81.92%) and chemical oxygen demand (73.74%) in actual wastewater. Its excellent electrocatalytic performance is achieved by regulating the electronic structure and the adsorption/desorption of the intermediate. This study discovers a new type of electrode materials for nitrate removal in wastewater.

Exogenous melatonin improves cadmium tolerance in Solanum nigrum L. without affecting its remediation potential.

Although Solanum nigrum L. is a phytoremediator for different metals, its growth and physiology are still influenced by toxic levels of cadmium (Cd). Thus, the development of eco-friendly strategies to enhance its tolerance, maintaining remediation potential is of special interest. The present work aimed to evaluate the effects of exogenous application of melatonin (MT) in the physiological and biochemical responses of S. nigrum and remediation potential exposed to Cd. After 30 days of exposure, the results revealed that Cd-mediated inhibitory effects on biomass and photosynthetic pigment synthesis were efficiently mitigated upon application of melatonin, without affecting Cd accumulation. Higher levels of Cd were found in roots, regardless of the pretreatment with the melatonin. Foliar application of melatonin, however, induced distinctive effects, lowering malondialdehyde (MDA), relative electrical conductivity (REL), and proline levels in shoots. These changes contributed to improvements in the water status, photosynthetic pigment synthesis, and biomass production of S. nigrum under Cd stresses. Overall, our results indicate a protective effect of melatonin on S. nigrum response to excess Cd, contributing to a better tolerance and growth rate, without disturbing its phytoremediation potential.Novelty statementAlthough Solanum nigrum L. is a phytoremediator for different metals, its growth and physiology are still influenced by toxic levels of cadmium. This study evaluated the potential of melatonin to boost S. nigrum defence against Cd toward a better growth rate and remediation potential.

Facile interface engineering of hierarchical flower spherical-like Bi-metal-organic framework microsphere/Bi2MoO6 heterostructure for high-performance visible-light photocatalytic tetracycline hydrochloride degradation.

The self-assembled Bi-based metal-organic framework microspheres (Bi-MOF-M) by nanorods were successfully constructed by the glycol-assisted solvothermal method. Using Bi-MOF-M as a homologous template, a petal-like Bi2MoO6 (BMO) layer was grown in situ on its surface to facilely construct a chemically bonded heterojunction interface, realizing a micro/nano hierarchical flower spherical-like Bi-MOF-M/BMO heterojunction composite photocatalyst. The as-prepared series of Bi-MOF-M/BMO-x catalysts show higher visible light catalytic performance for tetracycline hydrochloride (TC) degradation. Among them, Bi-MOF-M/BMO-0.3 has the optimal catalytic activity, and the degradation efficiency can reach 93.6% within 60 min of light irradiation with superior mineralization ability and structural stability, and the degradation kinetic constant is 6.12 times that of Bi-MOF-M and 5.69 times that of BMO, respectively. The homologously grown Bi-MOF-M/BMO chemically bonded heterojunction not only effectively broadens the spectral absorption range and enhances the absorption intensity but also promotes the efficient separation of photogenerated carriers through forming a favorable interfacial electric field and well-matched energy band alignment. A reasonable mechanism for the visible light degradation of TC by the Bi-MOF-M/BMO composite catalyst with h+ and 1O2 as the main reactive species is proposed. The micro/nano hierarchical structure of the Bi-MOF/BMO catalyst allows it to exhibit the easy recovery advantage of micron-scale materials while maintaining the high catalytic activity of the primary nano-components.

Visualization and quantification of cadmium accumulation, chelation and antioxidation during the process of vacuolar compartmentalization in the hyperaccumulator plant Solanum nigrum L.

Hyperaccumulators store metals in the vacuoles of leaf cells. To investigate the role of vacuolar compartmentalization in Cd accumulation, chelation and induced antioxidation, we quantified the amounts of total cadmium (Cd), Cd2+, glutathione (GSH) and reactive oxygen species (ROS) in leaf cells of Solanum nigrum L. The results confirmed that vacuoles were, indeed, the main storage compartments for Cd. We then found that with increased Cd treatment concentration, the proportion of vacuolar Cd in protoplasts showed its ultimate storage capacity (82.24 %-83.40 %), and the Cd concentration stored in the protoplast maintained at a certain level (73.81-77.46 mg L-1). Besides, studies on different forms of Cd showed that the chelation state was dominant in the protoplast. The large level appearance of Cd2+ outside the vacuole revealed the limitations of vacuolar Cd2+ sequestration. The relationships between the combined forms of Cd and GSH outside the vacuole (R2 = 0.9906) showed GSH was mainly distributed to important compartments for chelation, not to vacuoles. We also demonstrated the presence of ROS-induced oxidative stress and detoxification mediated by the antioxidant GSH in vacuoles, suggesting that sequestration into vacuoles is an active process accompanied by chelation and antioxidant-mediated detoxification.

Optimization of preparation parameters for environmentally friendly attapulgite functionalized by chitosan and its adsorption properties for Cd2.

This work focused on using attapulgite and chitosan as raw materials to improve the adsorption capacity of Cd2+ from the aqueous phase by optimizing the preparation experimental parameters. The modification parameters (attapulgite-chitosan mass ratio, calcination temperature, and time) were specifically studied and optimized. The results indicated that the mass ratio of attapulgite to chitosan was 1:4, the calcination temperature was 300 °C, and the calcination time was 1 h. Both raw and functionalized attapulgite samples were characterized by nitrogen adsorption-desorption isotherms at 77 K, X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and zeta potential analysis. A series of adsorption experiments showed that the pseudo-second-order kinetic model and Langmuir adsorption isotherm better corresponded with the adsorption characteristics of the newly prepared adsorbent, and the maximum adsorption amount of Cd2+ was 109.30 mg/g. Moreover, the effects of the pH value and coexisting cations on the Cd2+ adsorption in aqueous solution were investigated. Adsorption mechanism of Cd2+ on adsorbent might attribute to complexation, ion exchange reaction, and self-polarization.

Remediation potential of spent mushroom substrate on Cd pollution in a paddy soil.

To investigate the remediation potential of spent mushroom substrate (SMS) on Cd pollution in a paddy soil, a rice pot experiment was conducted to study the effects of SMS addition on the availability of Cd in soil and the uptake of Cd in rice tissues. Five percent of SMS from Pleurotus eryngii (SMS-A, treatment: A), SMS from Agaricus bisporus (SMS-B, treatment: B), or SMS-A plus SMS-B (1:1, treatment: A+B) were added into a Cd-contaminated paddy soil before planting, respectively. The treatment of no SMS amendment was set up as the control (CK). At the four main growth stages of rice, the soils and plant samples were collected to detect the soil properties, Cd concentration in soils and rice tissues, and Cd fractions in soils. Results indicated that the application of SMS-A, SMS-B, and A+B significantly increased soil pH by 14.0-22.9, 23.9-32.9, and 22.7-30%, organic matter (OM) contents by 12.9-31.5, 22.1-34.5, and 26.1-36.9% comparing with CK. While cation exchange capacities (CECs) were increased by 3.6-8.5, 4.9-13.1, and 0.4-10.0% in A, B, and A+B treatments, respectively, except those at the maturation stage in A and B treatments. However, the CaCl2-Cd concentrations in soils were significantly decreased by 64.8-77.9, 76.1-98.9, 73.2-98.9% in A, B, and A+B treatments, respectively, comparing with CK. The reduced availability of Cd was attributed to the changes of Cd from soluble to insoluble fractions in soils amended with SMS and resulted in the decreased Cd uptake in rice tissues. The Cd concentrations in roots significantly decreased by 22.8-36.9, 28.6-36.6, and 26.8-42.6%, while the Cd concentrations in straw decreased by 20.1-46.4, 9.3-41.6, and 16.0-49.1% in A, B, and A+B treatments, respectively. At the maturation stage, the Cd concentrations in brown rice were reduced by 17.7, 15.9, and 19.4% in A, B, and A+B treatments, respectively. Correlation analysis revealed that the Cd concentrations in rice roots, straws, and brown rice were all positively correlated with CaCl2-Cd concentrations of soils. Moreover, soil pH and OM were significantly negatively correlated with the Cd concentration in rice tissues, except that between soil pH and the Cd concentration in rice straws. Therefore, the reduced Cd availability in soil and uptake in rice plant tissues together with better soil nutrient conditions by SMS application improved the biomass of root and straw at heading, filling, and maturation stages and the rice production by 32.9-38.8% at the maturation stage. The combined application of SMS-A and SMS-B can be used as a potential method for remediation of Cd-contaminated paddy soil.

From luminescence quenching to high-efficiency phosphorescence: a theoretical study on the monomeric and dimeric forms of platinum(II) complexes with both 2-pyridylimidazol-2-ylidene and bipyrazolate chelates.

To develop solid-state light-emitting materials with high luminescence efficiency, determining the potential photophysics and luminescence mechanisms of the aggregation state remains a challenge and a priority. Here, we apply density functional theory to study the photophysical properties of a series of square planar Pt(ii) complexes in both monomeric and dimeric forms. We reveal that four monomeric Pt(ii) complexes are dominated by triplet ligand-to-ligand charge-transfer, and the lack of the triplet metal-to-ligand charge-transfer feature results in weak spin-orbit coupling (SOC), which leads to limited radiative rates; moreover, calculated nonradiative transition rates are one or two orders of magnitude higher than those radiative rates because a large amount of reorganization energy caused by the vibration of the bipyrazolate (bipz) ligand cannot be readily suppressed in the monomeric form. Therefore, four monomers exhibit photoluminescence quenching in CH2Cl2 solution in both theoretical calculations and experiments. However, in the solid state, the intense luminescence phenomenon indicates obviously distinct properties between the monomer and aggregation. We carried out a dimer model to interpret that the interaction of PtPt induces a metal-metal-to-ligand charge-transfer excimeric state, which leads more metal components to participate in the charge transfer and enhance the SOC effect. At the same time, the ligand vibration can be significantly reduced by the shortened distance, and there is a strong π-π packing interaction in the dimer; thus, an excellent quantum yield can be achieved in aggregation. In addition, we disclose that introducing bulky substituents bearing electron-donating groups at R' and R'' positions have little effect on the properties of the monomers; however, there is a benefit of restricting the internal reorganization energy through the intermolecular interaction when packing in the solid state. Therefore, substitutions can be tuned to improve the properties of monomers (such as emission energy and reorganization energy). We hope that our work will shine some light on Pt(ii) emitters in the fabrication of efficient OLEDs.

Impact of ΔEST on Delayed Fluorescence Rate, Lifetime, and Intensity Ratio of Tetrahedral Cu(I) Complexes: Theoretical Simulation in Solution and Solid Phases.

Profound understanding of the luminescence mechanism and structure-property relationship is vital for Cu(I) thermally activated delayed fluorescence (TADF) emitters. Herein, we theoretically simulated luminescent behavior in both solution and solid phases for two Cu(I) complexes and found the following: (i) The strengthened spin-orbit coupling (SOC) effect by more dx2-y2 orbital contributions and well-restricted structural distortion via remarkable intramolecular interaction in [Cu(dmp)(POP)]+ enable the emission at room temperature to be a mixture of direct phosphorescence (10%) and TADF (90%). (ii) Benefiting from enhanced steric hindrance and the electron-donating ability of the paracyclophane group, the narrowed S1-T1 energy separation (ΔEST) in [Cu(dmp)(phanephos)]+ accelerates the reverse intersystem crossing, promoting the TADF rate (1.88 × 105 s-1) and intensity ratio (98.3%). These results indicate that the small ΔEST is superior for reducing the lifetime and that the strong SOC stimulates the phosphorescence to compete with TADF, which are both conducive to avoiding collision-induced exciton quenching and reducing the roll-off in devices.

Capacity and potential mechanisms of Cd(II) adsorption from aqueous solution by blue algae-derived biochars.

The removal of potentially toxic metals by biochars is currently a popular and salutary method. In this study, we combined the advantages of blue algae (Microcystic) and pyrolysis technology to produce a late-model biochar. Moreover, the adsorption capacity and potential mechanisms of blue algae-derived biochars for the removal of cadmium (Cd) from aqueous solution were evaluated in comparison with the adsorption capacity and potential mechanisms of corn straw-derived biochar (CSBC) and rice husk-derived biochar (RHBC). Batch adsorption experiments were used to explore the adsorption performance of biochars, and a wide range of characterization techniques were employed: scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and zeta potential analysis. The results showed that the adsorption isotherms could be described well by the Langmuir model and that the pseudo-second-order model fit the Cd(II) adsorption kinetics best, indicating that the process was monolayer and controlled by chemisorption. Moreover, the Cd(II) removal capacity of optimal blue algae-derived biochar (BC600-2) (135.7 mg g-1) was 85.9% and 66.9% higher than the removal capacity of CSBC and RHBC, respectively. In addition, the results of the characterization methods showed that precipitation with minerals was the primary mechanism, accounting for 68.7-89.5% of the capacity. Overall, blue algae-derived biochars, as a product from freshwater biowaste, may be a novel and potentially valuable adsorbent for Cd(II) removal.

Molecular-Level Insight of Cu(I) Complexes with the 7,8-Bis(diphenylphosphino)-7,8-dicarba-nido-undecaborate Ligand as a Thermally Activated Delayed Fluorescence Emitter: Luminescent Mechanism and Design Strategy.

Investigation of the clear structure-property relationship and microscopic mechanism of thermally activated delayed fluorescence (TADF) emitters with high emission quantum yield is a direction worthy of continuous efforts. The instructive theoretical principle of TADF material design is critical and challenging. Here, we carried out theoretical calculation on two experimental Cu(I) complexes with the same 7,8-bis(diphenylphosphino)-7,8-dicarba-nido-undecaborate (dppnc) but different N^N ligands [dmbpy = 6,6'-dimethyl-2,2'-bipyridine (1) or dmp = 2,9-dimethyl-1,10-phenanthroline (2)] to briefly elaborate the structure-TADF performance relationship and luminescence mechanism. It was found that enhanced rigidity by the fused benzene ring between two pyridyl units in complex 2 leads to (i) higher allowedness of S1 → S0, (ii) more effective reverse intersystem crossing (RISC), and (iii) better relative stability of the T1 state, which could be responsible for its excellent TADF behavior. Thus, a strategy of extending π conjugation in the N^N ligand could be deduced to further enhance the quantum yield. We validated it and have succeeded in designing analogue complex 4 by extending π conjugation with an electron-withdrawing pyrazinyl. Benefiting from the smaller energy gap (ΔEST) and plunged reorganization energy between the S1 and T1 states, the rate of RISC in complex 4 (1.05 × 108 s-1) increased 2 orders of magnitude relative to that of 2 (5.80 × 106 s-1), showing more superiority of the TADF behavior through a better balance of RISC, fluorescence, and phosphorescence decay. Meanwhile, the thermally activated temperature of 4 is only 165 K, implying that there is a low-energy barrier. All of these indicate that the designed complex 4 may be a potential TADF candidate.