Inducing and Switching the Handedness of Polyacetylenes with Topologically Chiral [2]Catenane Pendants.

To explore the chirality induction and switching of topological chirality, poly[2]catenanes composed of helical poly(phenylacetylenes) (PPAs) main chain and topologically chiral [2]catenane pendants are described for the first time. These poly[2]catenanes with optically active [2]catenanes on side chains were synthesized by polymerization of enantiomerically pure topologically chiral [2]catenanes with ethynyl polymerization site and/or point chiral moiety. The chirality information of [2]catenane pendants was successfully transferred to the main chain of polyene backbones, leading to preferred-handed helical conformations, while the introduction of point chiral units has negligible effect on the overall helices. More interestingly, attributed to unique dynamic feature of the [2]catenane pendants, these polymers revealed dynamic response behaviors to solvents, temperature, and sodium ions, resulting in the fully reversible switching on/off of the chirality induction. This work provides not only new design strategy for novel chiroptical switches with topologically chiral molecules but also novel platforms for the development of smart chiral materials.

Tuning vibration-induced emission through macrocyclization and catenation.

In order to investigate the effect of macrocyclization and catenation on the regulation of vibration-induced emission (VIE), the typical VIE luminogen 9,14-diphenyl-9,14-dihydrodibenzo[a, c]phenazine (DPAC) was introduced into the skeleton of a macrocycle and corresponding [2]catenane to evaluate their dynamic relaxation processes. As investigated in detail by femtosecond transient absorption (TA) spectra, the resultant VIE systems revealed precisely tunable emissions upon changing the solvent viscosity, highlighting the key effect of the formation of [2]catenane. Notably, the introduction of an additional pillar[5]arene macrocycle featuring unique planar chirality endows the resultant chiral VIE-active [2]catenane with attractive circularly polarized luminescence in different states. This work not only develops a new strategy for the design of new luminescent systems with tunable vibration induced emission, but also provides a promising platform for the construction of smart chiral luminescent materials for practical applications.

[Effect of No-tillage on Soil Aggregates in Farmland：A Meta Analysis].

In order to clarify the impact of no-tillage on the quality of farmland soil aggregates in China and promote the adaptive application of no-tillage practices， a Meta-analysis was conducted by collecting data from 116 published studies. The effects of no-tillage on aggregate size distribution， mean weight diameter （MWD）， and aggregate-associated C were studied. The results showed that compared with that under tillage， no-tillage significantly increased the proportion of macroaggregates （10.9%） and MWD （12.8%） and decreased the proportion of clay and silt （-15.5%） but had no significant effect on soil microaggregate and aggregate-associated C. The subgroup and Meta regression analysis showed that no-tillage significantly increased the proportion of macroaggregates in Northwest China （17.6%） and MWD in North China （15.4%）. In upland and clay loam， no-tillage increased MWD by 12.6% and 18.4%， respectively. The effect of no-tillage on increasing the proportion of macroaggregates increased with the soil pH. When straw returned， no-tillage significantly increased the proportion of macroaggregates （9.6%） and MWD （11.6%）， but no significant effect of no-tillage on aggregates was found after straw removal. Regarding test duration， short-term （ < 5 a） no-tillage could significantly increase the proportion of macroaggregates， whereas long-term （ > 10 a） no-tillage could improve the MWD. In different soil layers， no-tillage could only significantly improve the aggregate size distribution and MWD in topsoil （0-20 cm） but had no effect in subsoil （ > 20 cm）. In summary， no-tillage could improve aggregate size distribution and stability but had no effect on aggregate-associated C. Production region， soil properties， field management methods， and other factors should be fully considered in production practice to effectively improve the quality of soil aggregates.

Dual Stimuli-Responsive [2]Rotaxanes with Tunable Vibration-Induced Emission and Switchable Circularly Polarized Luminescence.

Aiming at the construction of novel stimuli-responsive fluorescent system with precisely tunable emissions, the typical 9,14-diphenyl-9,14-dihydrodibenzo[a, c]phenazine (DPAC) luminogen with attractive vibration-induced emission (VIE) behavior has been introduced into [2]rotaxane as a stopper. Taking advantage of their unique dual stimuli-responsiveness towards solvent and anion, the resultant [2]rotaxanes reveal both tunable VIE and switchable circularly polarized luminescence (CPL). Attributed to the formation of mechanical bonds, DPAC-functionalized [2]rotaxanes display interesting VIE behaviors including white-light emission upon the addition of viscous solvent, as evaluated in detail by femtosecond transient absorption (TA) spectra. In addition, ascribed to the regulation of chirality information transmission through anion-induced motions of chiral wheel, the resolved chiral [2]rotaxanes reveal unique switchable CPL upon the addition of anion, leading to significant increase in the dissymmetry factors (glum ) values with excellent reversibility. Interestingly, upon doping the chiral [2]rotaxanes in stretchable polymer, the blend films reveal remarkable emission change from white light to light blue with significant 6.5-fold increase in glum values up to -0.035 under external tensile stresses. This work provides not only a new design strategy for developing molecular systems with fluorescent tunability but also a novel platform for the construction of smart chiral luminescent materials for practical use.

[Effect of Biochar on Agricultural Soil Aggregates and Organic Carbon: A Meta-analysis].

As a soil amendment, biochar has been widely used to ameliorate agricultural soil. To ensure the effect of biochar on the carbon sequestration of farmlands in China, a Meta-analysis was carried out via collecting published literatures. We quantitatively analyzed the response of biochar application to soil aggregates, aggregate carbon, and soil organic carbon to different experimental conditions. The results showed that the application of biochar significantly increased the proportion of soil macroaggregates(10.8%) and MWD(13.3%) but had no significant effect on soil microaggregates and silty-clay compared with those in the non-biochar-added treatment. Moreover, biochar addition significantly increased soil organic carbon content(56.9%), with the largest increased area in North China(39.4%), and enhanced intra-aggregate carbon contents of each particle size. Biochar could significantly increase soil organic carbon content under different experimental designs. Compared with that under non-fertilization, biochar combined with fertilization could also significantly improve soil structure and soil fertility. We also found that more than two years of biochar application significantly increased the proportion of macroaggregates(15.7%), MWD(21.2%), macroaggregate carbon(31.7%), and soil organic carbon(40.0%). Meanwhile, biochar produced from crop straw had better soil improvement effects than that of wood and sawdust. Biochar applied in high-nitrogen soil was more beneficial to improve soil stability. Thus, we concluded that biochar could meliorate soil structure and promote the accumulation of soil organic carbon, which was of importance for the fertility maintenance and improvement of the farmland.

Stimuli-responsive rotaxane-branched dendronized polymers with tunable thermal and rheological properties.

Aiming at the creation of polymers with attractive dynamic properties, herein, rotaxane-branched dendronized polymers (DPs) with rotaxane-branched dendrons attached onto the polymer chains are proposed. Starting from macromonomers with both rotaxane-branched dendrons and polymerization site, targeted rotaxane-branched DPs are successfully synthesized through ring-opening metathesis polymerization (ROMP). Interestingly, due to the existence of multiple switchable [2]rotaxane branches within the attached dendrons, anion-induced reversible thickness modulation of the resultant rotaxane-branched DPs is achieved, which further lead to tunable thermal and rheological properties, making them attractive platform for the construction of smart polymeric materials.

Photoresponsive Rotaxane-Branched Dendrimers: From Nanoscale Dimension Modulation to Macroscopic Soft Actuators.

Aiming at the construction of novel soft actuators through the amplified motions of molecular machines at the nanoscale, the design and synthesis of a new family of photoresponsive rotaxane-branched dendrimers through an efficient controllable divergent approach was successfully realized for the first time. In the third-generation rotaxane-branched dendrimers, up to 21 azobenzene-based rotaxane units located at each branch, thus making them the first successful synthesis of light-control integrated artificial molecular machines. Notably, upon alternative irradiation with UV and visible light, photoisomerization of the azobenzene stoppers leads to the collective and amplified motions of the precisely arranged rotaxane units, resulting in controllable and reversible dimension modulation of the integrating photoresponsive rotaxane-branched dendrimers in solution. Moreover, novel macroscopic soft actuators were further constructed based on these photoresponsive rotaxane-branched dendrimers, which revealed fast shape transformation behaviors with an actuating speed up to 21.2 ± 0.2° s-1 upon ultraviolet irradiation. More importantly, the resultant soft actuators could produce mechanical work upon light control that has been further successfully employed for weight-lifting and cargo transporting, thus laying the foundation toward the construction of novel smart materials that can perform programmed events.

[Structure and Function of Soil Fungal Community in Rotation Fallow Farmland in Alluvial Plain of Lower Yellow River].

This study was conducted to clarify the structure and function of the fungal community and the microecology change characteristics of farmland soil fertility response to different fallow rotation patterns. It aimed to provide a reference for promoting farmland ecological restoration and farmland quality improvement in the alluvial plain of the lower Yellow River. Farmland soil subject to a long-term rotation fallow experiment since 2018 was studied using Illumina MiSeq high-throughput sequencing technology, and the 'FUNGuild' fungal function prediction tool was used to analyze differences in soil fungal community structure and function under the following four rotation fallow regimes: long fallow (LF), winter wheat and summer fallow (WF), winter fallow and summer maize (FM), and annual rotation of winter wheat and summer maize (WM). The results showed that LF (fallow lasting two years) increased the richness and diversity of fungal communities in the topsoil (0-20 cm layer), whereas WF increased the richness and diversity of fungi in the deep soil (20-40 cm layer) after winter wheat harvest. A total of 2262 OTU were obtained from all soil samples, which were divided into 14 phyla, 34 classes, 75 orders, 169 families, 309 genera, and 523 species. OTU shared by the two soil layers included 420 types (0-20 cm layer) and 253 types (20-40 cm layer), respectively. The fungal community structure of the four rotation fallow soils was similar at the phylum level, mainly including Ascomycota, Basidiomycota, and Mortierellomycota. The total abundances of the three dominant bacteria were 91.69%-96.91% (0-20 cm layer) and 91.67%-94.86% (20-40 cm layer), respectively. Principal component analysis showed that the first principal component (PC1) and the second principal component (PC2) could explain the difference in community structure by 45.56% (0-20 cm layer) and 46.20% (20-40 cm layer). Additionally, the LDA results of LEfSe (threshold was 4.0) showed that there were 64 fungal evolutionary branches in LF, FM, WF, and WM with statistically significant differences (P<0.05). According to RDA analysis, total organic carbon (TOC), total phosphorus (TP), available nitrogen (AN), and soil water content (SWC) were the main environmental factors that significantly affected fungal community in the 0-40 cm soil layer (P<0.05). The functional prediction with FUNGuild showed that the main nutrient types among different treatments in different soil layers were saprotrophic, saprotrophic-symbiotrophic, pathotrophic-saprotrophic-symbiotrophic, and pathotrophic. In LF, the nutrient type of topsoil was mainly pathotrophic-saprotrophic-symbiotrophic, whereas in deep soil, the relative abundance of pathotrophic fungi was the highest. Additionally, in the treatments with planted wheat or corn (FM, WF, and WM), saprotrophic was the main type in both soil layers. Therefore, different fallow patterns were linked to variation in the structure, diversity, and nutrient types of soil fungal communities. Based on these results, seasonal fallow practices could regulate the farmland soil micro-ecological environment of intensive planting and promote the health and harmony of farmland soil ecosystems.

POSTHEMORRHAGIC SHOCK MESENTERIC LYMPH IMPAIRS SPLENIC DENDRITIC CELL FUNCTION IN MICE.

ABSTRACT: Dendritic cell (DC)-mediated immune dysfunction is involved in the process of severe hemorrhagic shock that leads to sepsis. Although post-hemorrhagic shock mesenteric lymph (PHSML) induces immune organs injuries and apoptosis, whether PHSML exerts adverse effects on splenic DCs remains unknown. In this study, we established a hemorrhagic shock model (40 ± 2 mm Hg for 60 min) followed by fluid resuscitation with the shed blood and equal Ringer's solution and drained the PHSML after resuscitation. At 3 h after resuscitation, we harvested the splenic tissue to isolate DCs using anti-CD11c immunomagnetic beads and then detected the necrotic and apoptotic rates in splenocytes and splenic DCs. We also detected the levels of TNF-α, IL-10, and IL-12 in the culture supernatants and surface marker expressions of MHC-II, CD80, and CD86 of splenic DCs following LPS stimulation for 24 h. Second, we purified the DCs from splenocytes of normal mice to investigate the effects of PHSML treatment on cytokine production and surface marker expression following LPS stimulation. The results showed that PHSML drainage attenuated LPS-induced cell death of splenocytes and DCs. Meanwhile, PHSML drainage enhanced the DC percentage in splenocytes and increased the TNF-α and IL-12 production by DCs and the expressions of CD80, CD86, and MHCII of DCs treated by LPS. Furthermore, PHSML treatment reduced the productions of TNF-α, IL-10, and IL-12 and the expressions of CD80 and CD86 in normal DCs after treatment with LPS. In summary, the current investigation demonstrated that PHSML inhibited the cytokine production and surface marker expressions of DCs stimulated by LPS, suggesting that PHSML plays an important role in hemorrhagic shock-induced immunosuppression through the impairment of DC function and maturation.

Multistate Circularly Polarized Luminescence Switching through Stimuli-Induced Co-Conformation Regulations of Pyrene-Functionalized Topologically Chiral [2]Catenane.

Aiming at the construction of novel circularly polarized luminescence (CPL) switches with multiple switchable emission states and high dissymmetry factors (glum ), topologically chiral [2]catenanes were employed as the key platform to construct a novel multistate CPL switching system. Taking advantage of the precise co-conformation regulations of the resultant pyrene-functionalized [2]catenanes under different external stimuli, reversible transformations between three emission states with different CPL performances, i.e. the initial "closed" form with a |glum | value of 0.012, the "open" form with an almost complete turn-off of CPL emission, and the "protonated" form with a boosted |glum | value of 0.022, were successfully realized. This study demonstrates the successful construction of not only the first topological chirality-based CPL switch, but also a novel bidirectional CPL switch, thus providing a promising platform for the construction of novel chiral materials.

Rotaxane-branched radical dendrimers with TEMPO termini.

The precise synthesis of novel rotaxane-branched radical dendrimers Gn-TEMPO (n = 1-3) with up to 24 TEMPO radicals as termini was successfully achieved, from which nanoparticles with a good longitudinal relaxivity were further prepared, thus making them potential candidates as promising contrast agents for magnetic resonance imaging.

Rotaxane Dendrimers: Alliance between Giants.

During recent decades, the blossoming of the field of mechanically interlocked molecules (MIMs), i.e., molecules containing mechanical or topological bonds such as rotaxanes, catenanes, and knots, has been reported in the literature. Taking advantage of the rapid development of diverse synthetic strategies, the precise control of both the architectures and topologies of MIMs has become realizable, which thus enables the construction of MIMs with specially desired functions. By mimicking biomolecular machines, a variety of MIM-based artificial molecular machines such as molecular shuttles, molecular muscles, molecular motors, and molecular assemblers have been constructed and operated by relying on the unique interlocked structures and controllable intramolecular movements. Two pioneers in this field, J. Fraser Stoddart and Jean-Pierre Sauvage, were awarded the 2016 Nobel Prize in Chemistry, thereby marking a golden age of MIMs. Along with the burgeoning of MIMs, the engineering of mechanical bonds into macromolecular scaffolds such as polymers or dendrimers has become an attractive topic since the targeted novel mechanically bonded macromolecules would feature interesting processable and mechanical properties, making them excellent candidates for practical applications such as device fabrication or smart materials. In particular, rotaxane dendrimers, attributed to the combination of the advantageous features of both rotaxanes (controllable dynamic motions) and dendrimers (nanoscale highly branched architectures), have evolved as versatile platforms for extensive applications such as gene delivery, light harvesting, and molecular nanoreactors. However, compared with the widely investigated polyrotaxanes and polycatenanes, in-depth investigations on rotaxane dendrimers have rarely been explored mainly because of the synthetic challenge that makes the preparation of diverse rotaxane dendrimers, especially high-generation ones, extremely difficult. During recent years, through the rational design and synthesis of organometallic rotaxane units as key building blocks, the employment of a controllable divergent approach led to the successful synthesis of a variety of rotaxane dendrimers with precise arrangements of rotaxane units as well as stimuli-responsive sites and functional groups. More importantly, on the basis of the synthetic accessibility to diverse rotaxane dendrimers, rotaxane dendrimers have been proven to hold great promise for extensive applications in diverse fields such as light harvesting, photocatalysis, and soft actuators. In this Account, we summarize our expedition in rotaxane dendrimers, including addressing the synthetic challenges, investigating their stimuli-responsive properties, expanding their potential applications, and inventing higher-order daisy chain dendrimers. We believe that this Account will inspire scientists from various disciplines to explore these appealing and versatile higher-order mechanically bonded macromolecules.

[Characteristics of Bacterial Community Structure in Fluvo-aquic Soil Under Different Rotation Fallow].

The aim of this study was to provide a reference for promoting ecological restoration of farmland and the green development of agriculture in the alluvial plain of the lower Yellow River by determining the effects of different rotation fallow patterns on the bacterial community of the fluvo-aquic soil. Farmland soil subject to a long-term rotation fallow experiment since 2018 was studied using Illumina MiSeq high-throughput sequencing technology, and the 'Tax4Fun' bacterial function prediction tool was used to analyze differences in soil bacterial community structure and function under the following four rotation fallow regimes:long fallow(LF), winter wheat and summer fallow(WF), winter fallow and summer maize(FM), and annual rotation of winter wheat and summer maize(WM). The environmental factors affecting changes in the soil bacterial community structure and function were also analyzed. In total, 44 phyla, 146 classes, 338 orders, 530 families, 965 genera, and 2073 species of bacteria were detected in the soil samples from the different rotation fallow regimes, and the dominant bacterial groups were Actinobacteria, Proteobacteria, Acidobacteria, and Chloroflexi in 0-20 cm and 20-40 cm soil layers. However, the relative abundances of the dominant bacteria groups were varied between the rotation fallow regimes. In the 0-20 cm layer of the seasonal fallow soils(WF and FM), bacteria were more abundant and community diversity was higher than that of the WM and LF soils. In 20-40 cm soil layer, the WF soil was more abundant in bacterial and the community was more diverse. Based on the prediction function of the 'Tax4Fun' tool, six primary metabolic pathways, 40 secondary metabolic pathways(18 types with relative abundance greater than 1%), and 264 tertiary metabolic pathways were identified in the soil bacteria of the different rotation fallow regimes. Seasonal fallow(WF and FM) was found to increase the relative abundance of beneficial bacterial metabolic pathways involved in metabolism, environmental information processing, and genetic information processing. According to RDA analysis, the soil bacterial community in the 0-20 cm soil layer was significantly affected by soil moisture, total phosphorus, available phosphorus, available potassium, pH, and C/N ratio(P<0.05), and the soil bacterial community in 20-40 cm soil layer was significantly affected by soil total phosphorus and available phosphorus(P<0.05). Therefore, different fallow patterns were linked to variation in the structure, diversity, and metabolic functions of soil bacterial communities. Based on these results, seasonal fallow practices could promote the health and stability of farmland soil ecosystems.

Self-Assembly of a Bilayer 2D Supramolecular Organic Framework in Water.

Accurate control of the layer number of orderly stacked 2D polymers has been an unsettled challenge in self-assembly. Herein we describe the fabrication of a bilayer 2D supramolecular organic framework from a monolayer 2D supramolecular organic framework in water by utilizing the cooperative coordination of a rod-like bipyridine ligands to zinc porphyrin subunits of the monolayer network. The monolayer supramolecular framework is prepared from the co-assembly of an octacationic zinc porphyrin monomer and cucurbit[8]uril (CB[8]) in water through CB[8]-encapsulation-promoted dimerization of 4-phenylpyridiunium subunits that the zinc porphyrin monomer bear. The bilayer 2D supramolecular organic framework exhibits structural regularity in both solution and the solid state, which is characterized by synchrotron small-angle X-ray scattering and high-resolution transmission electron microscopic techniques. Atomic force microscopic imaging confirms that the bilayer character of the 2D supramolecular organic framework can be realized selectively on the micrometer scale.

Artificial Light-Harvesting Systems Based on AIEgen-branched Rotaxane Dendrimers for Efficient Photocatalysis.

Aiming at the construction of novel platform for efficient light harvesting, the precise synthesis of a new family of AIEgen-branched rotaxane dendrimers was successful realized from an AIEgen-functionalized [2]rotaxane through a controllable divergent approach. In the resultant AIE macromolecules, up to twenty-one AIEgens located at the tails of each branches, thus making them the first successful example of AIEgen-branched dendrimers. Attributed to the solvent-induced switching feature of the rotaxane branches, the integrated rotaxane dendrimers displayed interesting dynamic feature upon the aggregation-induced emission (AIE) process. Moreover, novel artificial light-harvesting systems were further constructed based on these AIEgen-branched rotaxane dendrimers, which revealed impressive generation-dependent photocatalytic performances for both photooxidation reaction and aerobic cross-dehydrogenative coupling (CDC) reaction.

A Two-Dimensional Metallacycle Cross-Linked Switchable Polymer for Fast and Highly Efficient Phosphorylated Peptide Enrichment.

The selective and efficient capture of phosphopeptides is critical for comprehensive and in-depth phosphoproteome analysis. Here we report a new switchable two-dimensional (2D) supramolecular polymer that serves as an ideal platform for the enrichment of phosphopeptides. A well-defined, positively charged metallacycle incorporated into the polymer endows the resultant polymer with a high affinity for phosphopeptides. Importantly, the stimuli-responsive nature of the polymer facilitates switchable binding affinity of phosphopeptides, thus resulting in an excellent performance in phosphopeptide enrichment and separation from model proteins. The polymer has a high enrichment capacity (165 mg/g) and detection sensitivity (2 fmol), high enrichment recovery (88%), excellent specificity, and rapid enrichment and separation properties. Additionally, we have demonstrated the capture of phosphopeptides from the tryptic digest of real biosamples, thus illustrating the potential of this polymeric material in phosphoproteomic studies.

Hierarchical Self-Assembly of Nanowires on the Surface by Metallo-Supramolecular Truncated Cuboctahedra.

Parastichy, the spiral arrangement of plant organs, is an example of the long-range apparent order seen in biological systems. These ordered arrangements provide scientists with both an aesthetic challenge and a mathematical inspiration. Synthetic efforts to replicate the regularity of parastichy may allow for molecular-scale control over particle arrangement processes. Here we report the packing of a supramolecular truncated cuboctahedron (TCO) into double-helical (DH) nanowires on a graphite surface with a non-natural parastichy pattern ascribed to the symmetry of the TCOs and interactions between TCOs. Such a study is expected to advance our understanding of the design inputs needed to create complex, but precisely controlled, hierarchical materials. It is also one of the few reported helical packing structures based on Platonic or Archimedean solids since the discovery of the Boerdijk-Coxeter helix. As such, it may provide experimental support for studies of packing theory at the molecular level.

Acid-Activated Motion Switching of DB24C8 between Two Discrete Platinum(II) Metallacycles.

The precise operation of molecular motion for constructing complicated mechanically interlocked molecules has received considerable attention and is still an energetic field of supramolecular chemistry. Herein, we reported the construction of two tris[2]pseudorotaxanes metallacycles with acid-base controllable molecular motion through self-sorting strategy and host-guest interaction. Firstly, two hexagonal Pt(II) metallacycles M1 and M2 decorated with different host-guest recognition sites have been constructed via coordination-driven self-assembly strategy. The binding of metallacycles M1 and M2 with dibenzo-24-crown-8 (DB24C8) to form tris[2]pseudorotaxanes complexes TPRM1 and TPRM2 have been investigated. Furthermore, by taking advantage of the strong binding affinity between the protonated metallacycle M2 and DB24C8, the addition of trifluoroacetic acid (TFA) as a stimulus successfully induces an acid-activated motion switching of DB24C8 between the discrete metallacycles M1 and M2. This research not only affords a highly efficient way to construct stimuli-responsive smart supramolecular systems but also offers prospects for precisely control multicomponent cooperative motion.

AIE-Active Chiral [3]Rotaxanes with Switchable Circularly Polarized Luminescence.

The construction of circularly polarized luminescence (CPL) switches with multiple switchable emission states and high dissymmetry factors (glum ) has attracted increasing attention due to their broad applications in diverse fields such as the development of smart devices and sensors. Herein, a new family of AIE-active chiral [3]rotaxanes were designed and synthesized, from which a novel CPL switching system was successfully constructed. The switching process was realized through the controlled motions of the chiral pillar[5]arene macrocycles along the axle through the addition or removal of the acetate anions, which not only modulated the chirality information transfer but also tuned the aggregations of the integrated [3]rotaxanes, thus resulting in reversible transformations between two emission states with both high photoluminescence quantum yields (PLQYs) and high dissymmetry factors (glum ) values.

Orthogonal Self-Assembly of a Two-Step Fluorescence-Resonance Energy Transfer System with Improved Photosensitization Efficiency and Photooxidation Activity.

During the past few decades, fabrication of multistep fluorescence-resonance energy transfer (FRET) systems has become one of the most attractive topics within supramolecular chemistry, chemical biology, and materials science. However, it is challenging to efficiently prepare multistep FRET systems with precise control of the distances between locations and the numbers of fluorophores. Herein we present the successful fabrication of a two-step FRET system bearing specific numbers of anthracene, coumarin, and BODIPY moieties at precise distances and locations through an efficient and controllable orthogonal self-assembly approach based on metal-ligand coordination and host-guest interactions. Notably, the photosensitization efficiency and photooxidation activity of the two-step FRET system gradually increased with the number of energy transfer steps. For example, the two-step FRET system exhibited 1.5-fold higher 1O2 generation efficiency and 1.2-fold higher photooxidation activity than that of its corresponding one-step FRET system. This research not only provides the first successful example of the efficient preparation of multistep FRET systems through orthogonal self-assembly involving coordination and host-guest interactions but also pushes multistep FRET systems toward the application of photosensitized oxidation of a sulfur mustard simulant.