Unequal Perylene Diimide Twins in a Quadruple Assembly.

Natural light-harvesting (LH) systems can divide identical dyes into unequal aggregate states, thereby achieving intelligent "allocation of labor". From a synthetic point of view, the construction of such kinds of unequal and integrated systems without the help of proteinaceous scaffolding is challenging. Here, we show that four octatetrayne-bridged ortho-perylene diimide (PDI) dyads (POPs) self-assemble into a quadruple assembly (POP)4 both in solution and in the solid state. The two identical PDI units in each POP are compartmentalized into weakly coupled PDIs (P520) and closely stacked PDIs (P550) in (POP)4 . The two extreme pools of PDI chromophores were unambiguously confirmed by single-crystal X-ray crystallography and NMR spectroscopy. To interpret the formation of the discrete quadruple assembly, we also developed a two-step cooperative model. Quantum-chemical calculations indicate the existence of multiple couplings within and across P520 and P550, which can satisfactorily describe the photophysical properties of the unequal quadruple assembly. This finding is expected to help advance the rational design of dye stacks to emulate functions of natural LH systems.

The capacity of ion adsorption and purification for coniferous forests is stronger than that of broad-leaved forests.

In the past few decades, industrialization has caused a large number of pollutants to be released into the atmosphere. Forest ecosystems play an important function in regulating the biogeochemistry and the circulation of metal ions pollutants. Forest ecosystems affect the absorption of pollutants and dissolution of nutrients from the atmosphere and vegetation canopy, thereby influencing the content and composition of forest floor leachate and soil solution. This study examined changes in acid anions (NO3-, SO42-, Cl-) and metal cations (K+, Ca2+, Na2+, Mg2+, Fe3+, Pb2+, Cu2+, Cd2+) in rainfall, throughfall, stemflow, and forest floor leachate for five different forests (Larix principis-rupprechtii, Picea wilsonii, Picea crassifolia, Betula platyphylla and Rhododendron communities). The results showed that the enrichment capacity of acid anions and metal cations in the vegetation canopy of the coniferous forests (L. principis-rupprechtii, P. wilsonii, P. crassifolia) was stronger than that of the broad-leaved forests (B. platyphylla and Rhododendron communities). The content of acid anions and metal cations in stemflow of coniferous forests were 3.7-5.6 times and 0-9.3 times higher than those of broad-leaved forests, respectively. Corresponding values in throughfall were 1-1.4 times and 0.3-2.4 times, respectively. The contents of NO3-, Cl-, K+, Mg2+, Fe3+, Pb2+, Cu2+, and Cd2+ in leachate filtered from the soil layers that are deepening gradually showed consistent decreasing trend for all the forest stands. In addition, NO3-, Cl-, K+, Mg2+, Fe3+, and Pb2+ were also concentrated in the topsoil, except for Cu2+ and Cd2+. Nevertheless, SO42- and Na+ were concentrated in the subsoil, whereas Ca2+ was concentrated in the upper soil layers. Soil organic carbon (SOC) and total nitrogen (TN) contents in coniferous forest stands were 20-37% and 34-63% higher than those in broad-leaved forest stands, respectively. This results also shown that the contents of OC and TN has a strong correlation with the content of partial metal cations in soil and litter, indicating that coniferous forest stands had stronger ion scavenging and adsorption capacity in soil layer and litter layer than broad-leaved forest stands. Therefore, L. principis-rupprechtii, P. wilsonii, P. crassifolia had higher air pollutant adsorption and soil pollution remediation capacities than the other two forests. Thus, we recommend planting coniferous tree species (L. principis-rupprechtii, P. wilsonii and P. crassifolia) for eco-rehabilitation and water purification to improve the ecological service function of forest ecosystems.

Metal-organic frameworks embedded in a liposome facilitate overall photocatalytic water splitting.

Metal-organic frameworks (MOFs) have been studied extensively in the hydrogen evolution reaction (HER) and the water oxidation reaction (WOR) with sacrificial reagents, but overall photocatalytic water splitting using MOFs has remained challenging, principally because of the fast recombination of photo-generated electrons and holes. Here we have integrated HER- and WOR-MOF nanosheets into liposomal structures for separation of the generated charges. The HER-MOF nanosheets comprise light-harvesting Zn-porphyrin and catalytic Pt-porphyrin moieties, and are functionalized with hydrophobic groups to facilitate their incorporation into the hydrophobic lipid bilayer of the liposome. The WOR-MOF flakes consist of [Ru(2,2'-bipyridine)3]2+-based photosensitizers and Ir-bipyridine catalytic centres, and are localized in the hydrophilic interior of the liposome. This liposome-MOF assembly achieves overall photocatalytic water splitting with an apparent quantum yield of (1.5 ± 1)% as a result of ultrafast electron transport from the antennae (Zn-porphyrin and [Ru(2,2'-bipyridine)3]2+) to the reaction centres (Pt-porphyrin and Ir-bipyridine) in the MOFs and efficient charge separation in the lipid bilayers.

Soil fungal taxonomic diversity along an elevation gradient on the semi-arid Xinglong Mountain, Northwest China.

Elevation gradients, often regarded as "natural experiments or laboratories", can be used to study changes in the distribution of microbial diversity related to changes in environmental conditions that typically occur over small geographical scales. We exploited this feature by characterizing fungal composition and diversity along an elevation gradient on Xinglong Mountain, northwest China. For this, we used MiSeq sequencing to obtain fungal sequences and clustered them into operational taxonomic units (OTUs). In total, we obtained 1,203,302 reads, 133,700 on average in each sample of soil collected at three selected elevations (2807, 3046, and 3536 m). The reads were assigned to 2192 OTUs. Inconsistent variations were observed in fungal alpha-diversity in samples from the three elevations. However, Principal Coordinate Analysis based on Bray-Curtis and UniFrac (weighted and unweighted) distance metrics revealed that fungal communities in soil samples from 3046 and 3536 m elevations were most similar. Principal Component Analysis based on relative abundances of shared OTUs confirmed that OTUs in samples from 3536 m elevation were more closely related to OTUs from 3046 m than samples from 2807 m elevation. Ascomycota, Basidiomycota, Glomeromycota, Cercozoa and Chytridiomycota were the most abundant fungal phyla across the elevation gradient. Our study also provides valuable indications of relations between fungal communities and an array of soil chemical properties, and variations in fungal taxonomic diversity across a substantial elevation gradient.

Nanoscale Metal-Organic Frameworks and Metal-Organic Layers with Two-Photon-Excited Fluorescence.

Metal-organic frameworks (MOFs) based on 9,10-diphenylanthracene-derived ligands had been reported to exhibit upconverted fluorescence through triplet-triplet annihilation. We found that zirconium MOFs based on 9,10-diphenylanthracene can also give upconverted fluorescence via two-photon absorption without adding a triplet photosensitizer when a femtosecond pulsed laser is used as the excitation source. By tuning the synthetic condition, we obtained nanoscale MOFs of UiO structure in both octahedral and hexagonal nanoplate shapes, as well as a hexagonal nanoplate of MOFs of hcp-UiO structure and two-dimensional metal-organic layers. All of them, as well as a homogeneous solution of the 9,10-diphenylanthracene ligand, exhibit upconverted fluorescence upon excitation using a laser pulse of 60 fs with a pulse energy of ∼1.1 × 106 nJ/cm2 (unfocused). Moreover, we observed different emission spectra by two-photon excitation compared to those by one-photon excitation, which indicates access to a unique initial excited state via two-photon excitation. This phenomenon is not observed for a homogeneous solution of the ligand. These nanoscale MOFs may find application in two-photon fluorescence imaging.

Processing-Friendly Slot-Die-Cast Nonfullerene Organic Solar Cells with Optimized Morphology.

The power conversion efficiencies (PCEs) of spin-coated organic solar cells (OSCs) have increased rapidly in recent years. However, spin-coating shows poor reproducibility for large-scale production. Slot-die coating, a lab-scale version of roll-to-roll fabrication, has been considered as the most suitable technique for the production of future large-area commercial devices. For this, the highly efficient slot-die-fabricated devices are required to approach the performance of spin-cast OSCs. We present here, a nonfullerene OSC device utilizing the PBDB-T/i-IEICO-4F blend, fabricated by slot-die coating without post-treatment in the ambient conditions. The device showed an impressive PCE of 12.5%, which is one of the highest reported performance for slot-die-coated OSC devices. Compared to the spin-coated and blade-coated films with optimized thermal annealing time, the films fabricated by slot-die coating (without any treatment) exhibit not only the highest degree of crystallinity and face-on orientation but also the smallest domain size and the purest phase toward enhanced and balanced carrier mobilities. An enhanced excited-state charge generation has been attributed to transient charge kinetics using ultrafast spectroscopic signatures. The optimized slot-die-coated devices exhibit excellent tolerance for the increased thickness of the photoactive layer, attributing to favorable molecular packing. We used slot-die coating as a simple fabrication technique, which is capable of yielding highly efficient OSCs.

Energy transfer on a two-dimensional antenna enhances the photocatalytic activity of CO2 reduction by metal-organic layers.

Excited state energies on a two-dimensional light-harvesting metal-organic layer (MOL) are efficiently transported to Re- and Ir-based reaction centers for converting CO2 to CO or HCOOH. Such energy transfer enhances the photocatalytic CO2 reduction activity because it enables multiple photo-electron injections in a short time period in the photocatalysis.

Ecohydrological effects of biocrust type on restoration dynamics in drylands.

Global climate change influences not only vascular plants, but also biological soil crusts (biocrusts), which play important roles in dryland vegetation dynamics by redistributing rainfall in soils. Different types of biocrusts, spanning a spectrum from cyanobacteria-dominated and moss-dominated, have distinct roles in rainfall redistribution patterns, but the ecohydrological effects of different biocrust types on dryland ecosystem dynamics remain largely unclear. This study developed an ecohydrological model with biocrust as a system state variable to explicitly explore the effects of different biocrust types on dryland vegetation dynamics in Shapotou region in northern China, particularly after restoration. The results indicated that both cyanobacteria- and moss-dominated biocrusts could support high grass cover (approximately 40%) after restoration. Cyanobacterial, but not moss biocrusts, could also maintain a high level of shrub cover (13 and 3%, respectively). Shifting from cyanobacteria to mosses gradually increased the biocrust cover from approximately 40% to 80%. The biocrust's water-holding capacity (the volume of water it can intercept per unit area) is likely be able to explain the dynamics of biocrust and shrub cover (with correlation efficiency of R2 = 0.972 and 0.987, respectively), but not grass cover (R2 = 0.224). The findings suggest that biocrust type may significantly affect coverage of biocrusts and shrubs, but not grass coverage, and global climate change may influence dryland restoration by altering biocrust types.

Simulating Powder X-ray Diffraction Patterns of Two-Dimensional Materials.

Powder X-ray diffraction (PXRD) is widely used to study atomic arrangements in ordered materials. The Bragg equation, which describes diffraction of a three-dimensional crystal, fails in two-dimensional (2D) cases. Complete integration of diffraction signals from a continuum instead of discrete directions in the Bragg equation is thus required for proper data interpretation of 2D materials. Furthermore, modeling of preferred orientation of the 2D crystals as well as geometric disorders are also of vital importance. Here, we present a complete integration method in real space (CIREALS) for PXRD simulation of monolayer or multilayer 2D crystals, especially 2D metal-organic layers and 2D covalent organic frameworks. By working in real space instead of reciprocal space, we can readily capture the 2D geometry and preferred orientation of these materials. The predicted PXRD patterns by CIREALS facilitates structure analysis of these new types of 2D material.

Warm-White-Light-Emitting Diode Based on a Dye-Loaded Metal-Organic Framework for Fast White-Light Communication.

A dye@metal-organic framework (MOF) hybrid was used as a fluorophore in a white-light-emitting diode (WLED) for fast visible-light communication (VLC). The white light was generated from a combination of blue emission of the 9,10-dibenzoate anthracene (DBA) linkers and yellow emission of the encapsulated Rhodamine B molecules. The MOF structure not only prevents dye molecules from aggregation-induced quenching but also efficiently transfers energy to the dye for dual emission. This light-emitting material shows emission lifetimes of 1.8 and 5.3 ns for the blue and yellow components, respectively, which are significantly shorter than the 200 ns lifetime of Y3Al5O12:Ce3+ in commercial WLEDs. The MOF-WLED device exhibited a modulating frequency of 3.6 MHz for VLC, six times that of commercial WLEDs.

Exciton Migration and Amplified Quenching on Two-Dimensional Metal-Organic Layers.

The dimensionality dependency of resonance energy transfer is of great interest due to its importance in understanding energy transfer on cell membranes and in low-dimension nanostructures. Light harvesting two-dimensional metal-organic layers (2D-MOLs) and three-dimensional metal-organic frameworks (3D-MOFs) provide comparative models to study such dimensionality dependence with molecular accuracy. Here we report the construction of 2D-MOLs and 3D-MOFs from a donor ligand 4,4',4″-(benzene-1,3,5-triyl-tris(ethyne-2,1-diyl))tribenzoate (BTE) and a doped acceptor ligand 3,3',3″-nitro-4,4',4″-(benzene-1,3,5-triyl-tris(ethyne-2,1-diyl))tribenzoate (BTE-NO2). These 2D-MOLs and 3D-MOFs are connected by similar hafnium clusters, with key differences in the topology and dimensionality of the metal-ligand connection. Energy transfer from donors to acceptors through the 2D-MOL or 3D-MOF skeletons is revealed by measuring and modeling the fluorescence quenching of the donors. We found that energy transfer in 3D-MOFs is more efficient than that in 2D-MOLs, but excitons on 2D-MOLs are more accessible to external quenchers as compared with those in 3D-MOFs. These results not only provide support to theoretical analysis of energy transfer in low dimensions, but also present opportunities to use efficient exciton migration in 2D materials for light-harvesting and fluorescence sensing.

Two-Dimensional Metal-Organic Layers as a Bright and Processable Phosphor for Fast White-Light Communication.

A metal-organic layer (MOL) is a new type of 2D material that is derived from metal-organic frameworks (MOFs) by reducing one dimension to a single layer or a few layers. Tetraphenylethylene-based tetracarboxylate ligands (TCBPE), with aggregation-induced emission properties, were assembled into the first luminescent MOL by linking with Zr6 O4 (OH)6 (H2 O)2 (HCO2 )6 clusters. The emissive MOL can replace the lanthanide phosphors in white light emitting diodes (WLEDs) with remarkable processability, color rendering, and brightness. Importantly, the MOL-WLED exhibited a physical switching speed three times that of commercial WLEDs, which is crucial for visible-light communication (VLC), an alternative wireless communication technology to Wi-Fi and Bluetooth, by using room lighting to carry transmitted signals. The short fluorescence lifetime (2.6 ns) together with high quantum yield (50 %) of the MOL affords fast switching of the assembled WLEDs for efficient information encoding and transmission.

Graphene-Based Fluorescence-Quenching-Related Fermi Level Elevation and Electron-Concentration Surge.

Intermolecular p-orbital overlaps in unsaturated π-conjugated systems, such as graphene and fluorescent molecules with aromatic structure, serve as the electron-exchanged path. Using Raman-mapping measurements, we observe that the fluorescence intensity of fluorescein isothiocyanate (FITC) is quenched by graphene, whereas it persists in graphene-absent substrates (SiO2). After identifying a mechanism related to photon-induced electron transfer (PET) that contributes to this fluorescence quenching phenomenon, we validate this mechanism by conducting analyses on Dirac point shifts of FITC-coated graphene. From these shifts, Fermi level elevation and the electron-concentration surge in graphene upon visible-light impingements are acquired. Finally, according to this mechanism, graphene-based biosensors are fabricated to show the sensing capability of measuring fluorescently labeled-biomolecule concentrations.

Förster Energy Transport in Metal-Organic Frameworks Is Beyond Step-by-Step Hopping.

Metal-organic frameworks (MOFs) with light-harvesting building blocks designed to mimic photosynthetic chromophore arrays in green plants provide an excellent platform to study exciton transport in networks with well-defined structures. A step-by-step exciton random hopping model made of the elementary steps of energy transfer between only the nearest neighbors is usually used to describe the transport dynamics. Although such a nearest neighbor approximation is valid in describing the energy transfer of triplet states via the Dexter mechanism, we found it inadequate in evaluating singlet exciton migration that occurs through the Förster mechanism, which involves one-step jumping over longer distance. We measured migration rates of singlet excitons on two MOFs constructed from truxene-derived ligands and zinc nodes, by monitoring energy transfer from the MOF skeleton to a coumarin probe in the MOF cavity. The diffusivities of the excitons on the frameworks were determined to be 1.8 × 10(-2) cm(2)/s and 2.3 × 10(-2) cm(2)/s, corresponding to migration distances of 43 and 48 nm within their lifetimes, respectively. "Through space" energy-jumping beyond nearest neighbor accounts for up to 67% of the energy transfer rates. This finding presents a new perspective in the design and understanding of highly efficient energy transport networks for singlet excited states.

Study on the diffusion mechanism of graphene grown on copper pockets.

A correlation between graphene domains grown on the outer and the inner surfaces of Cu pockets is found, which discloses a new graphene growth mechanism based on the fast diffusion of carbon atoms through the 25 micro-meter-thick Cu foil, confirmed by isotopic labeling. Subsequently, on the outer surface of the Cu pocket, bilayer graphene with a coverage of about 78% is grown.

Large-energy, wavelength-tunable, all-fiber passively Q-switched Er:Yb-codoped double-clad fiber laser with mono-layer chemical vapor deposition graphene.

We demonstrate a large-energy, wavelength-tunable, all-fiber passively Q-switched Er:Yb-codoped laser using a mono-layer chemical vapor deposition (CVD) graphene saturable absorber (SA). By exploiting the large laser gain of Er:Yb double-clad fiber and optimizing the coupling ratio of the output coupler, not only can the mono-layer CVD graphene SA be protected from oversaturation and thermal damage, but also a large pulse energy up to 1.05 µJ (corresponding to the average output power of 25.6 mW) is thus achieved. Using a tunable fiber Fabry-Perot filter, stable Q-switched pulses can operate with a tunable range from 1530.97 to 1546.92 nm, covering a wavelength range of ∼16 nm. The Q-switching states at the different lasing wavelengths have been observed and recorded. The Q-switched repetition rate and the pulse duration (with the minimum one of 2.6 µs) have been characterized as well. This is, to the best of our knowledge, the largest pulse energy from an all-fiber graphene Q-switched laser.