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We report a novel family of boraolympicenes with fully-fused boron-doping at their π-skeletons. The resulting boraolympicenyl radical anion featured a resonant stability under inert conditions benefiting from the borataalkene-containing aromatic resonant form.

Atomically precise synthesis of topological molecular carbons such as Möbius carbon nanobelts (MCNBs) represents a big challenge in synthetic organic chemistry as it requires careful control of both twist and strain. So far, only one singly twisted MCNB has been reported and the MCNBs with more than two twists remain unknown. Herein, we report the facile synthesis of the first triply twisted MCNB by rational design and via a synthetic route involving Suzuki coupling-mediated macrocyclization, Bi(OTf)3-catalyzed cyclization of vinyl ethers, followed by oxidative dehydrogenation. The Möbius band-like structure was unambiguously confirmed by X-ray crystallographic analysis, which also revealed coexistence of (P,P,P)- and (M,M,M)- enantiomers. The racemic isomers were resolved by chiral HPLC and the isolated enantiomers exhibited a large absorption dissymmetry factor (|gabs| = 0.019) according to circular dichroism spectroscopy, which can be explained by the fully conjugated structure and the desirable orientation of the electric and magnetic transition moments.

Large graphene-like molecules with four zigzag edges are ideal gain medium materials for organic near-infrared (NIR) lasers. However, synthesizing them becomes increasingly challenging as the molecular size increases. In this study, we introduce a new intramolecular radical-radical coupling approach and successfully synthesize two fused triangulene dimers (1a/1b) efficiently. X-ray crystallographic analysis of 1a indicates that there is no intermolecular π-π stacking in the solid state. When the more soluble derivative 1b is dispersed in polystyrene thin films, amplified spontaneous emission in the NIR region is observed. Using 1b as the active gain material, we fabricate solution-processed distributed feedback lasers that exhibit a narrow emission linewidth at around 790 nm. The laser devices also exhibit low thresholds with high photostability. Our study provides a new synthetic strategy for extended nanographenes, which have diverse applications in electronics and photonics. J.W. acknowledges financial support from the NRF Investigatorship Award (NRF-NRFI05-2019-0005), the A*STAR AME grant (A20E5c0089) and start-up grant from the Joint School of National University of Singapore and Tianjin University@Fuzhou. The group at the University of Alicante thanks financial support from the “Ministerio de Ciencia e Innovación” (MCIN) of Spain and the European Regional Development Fund (grant No. PID2020-119124RB-I00) and from the Generalitat Valenciana though grant No. AICO/2021/093. Besides, this study part of the Advanced Materials program supported by the Spanish MCIN with funding from European Union NextGenerationEU and by Generalitat Valenciana (grant no. MFA/2022/045). Z.S. is grateful to the financial support from National Natural Science Foundation of China (Grant No. 21971187, 22222110), Natural Science Foundation of Tianjin (19JCJQJC62700) and the Haihe Laboratory of Sustainable Chemical Transformations.

Enantioselective ring-contraction reactions have not been widely reported. We have developed an enantioselective ring contraction of 5,6-dihydro-2H-benzo[b][1,4]oxazocines, affording enantiomerically enriched 3,4-dihydro-2H-1,4-benzoxazine derivatives as single regioisomers. An acidic additive is necessary in order to obtain the products with good yields and enantiomeric ratios (up to 93% yield, 98:2 er). The reaction was successfully performed on a gram scale, and the products can be derivatized easily.

Faced with the real demand of manufacturing industry to achieve the goal of green and high-quality development, exploring spatiotemporal heterogeneity and the spatial spillover effect of green manufacturing efficiency under environmental regulation can help reveal the path and mechanism of green development in the manufacturing industry. By using the SBM-DEM model to measure green manufacturing efficiency at the urban scale in China, exploratory spatial analysis is used to characterize the spatiotemporal differentiation of urban green manufacturing efficiency from 2003 to 2018. With the help of the spatial Durbin model, the impact of environmental regulation on green manufacturing efficiency and the spatial spillover effect are demonstrated. The results show that: (1) The green manufacturing efficiency of cities has developed in a gradual and balanced manner in time series, and the degree of equalization is stronger in the eastern coast than in the western inland; (2) Urban green manufacturing efficiency patterns are misaligned with economic scale patterns, indicating that green manufacturing is not traditionally dominated by economic factor inputs; (3) The practice of Chinese cities has proved that environmental regulation can significantly inhibit the development of green manufacturing efficiency in local cities. The crowding-out effect and optimization effect of environmental regulation on other external factors indirectly affect green development. By comparing different spatial weight matrices, it is shown that the economic relationship between cities can offset the inhibition of environmental regulation; (4) Although environmental regulation under spatial interaction would have significantly contributed to the green manufacturing efficiency of neighboring cities, this contribution effect is insignificant and weak due to the economic interactions between cities. Empirical research provides a theoretical foundation for the development of green manufacturing from the standpoint of environmental regulation, allowing green development research in manufacturing to move further.

The water entry process associated with complicated unsteady structures, with consideration of the influence of the waves, is not well studied. In the present work, the oblique water entry of a cylinder under different regular waves is numerically investigated. The volume of fluid (VOF) method and the sub-grid scale (SGS) stress model based on the large eddy simulation (LES) method are adopted for the 3-D simulation with six degrees of freedom. The present numerical model is based on a wave model, and as shown by the previous work that the predicted cavity evolution in the calm water agrees well with the experimental results. The present model is validated and it is shown that it could be used to predict the correct wave periods and fluctuations. The cavity evolution mechanism, the dynamic characteristics and the vortex structures are analyzed. The cavity of the water entry with waves closes more quickly than in the calm water case. Finally, several parametric studies of the water entry with different wave heights and water entry locations are carried out. The results provide insights into the effects of the waves on the cavity dynamics for oblique water entry problems.

The incorporation of organic radicals into coordination polymers was considered as a promising strategy to promote metal-ligand exchange interactions, but there are only a very limited number of stable organic radical-based ligands that can serve well such a purpose. Herein, we report two new tris(2,4,6-trichlorophenyl)methyl (TTM) radical-based ligands L1 and L2 with two and three imidazole substituents, respectively. The imidazole unit serves as a coordination site and it can also stabilize the TTM radical by intramolecular donor-acceptor interaction. Coordination of L1 and L2 with cobalt(II) ions gave the corresponding one- (CoCP-1) and two-dimensional (CoCP-2) coordination polymers, the structures of which were confirmed by X-ray crystallographic analysis. Magnetic measurements and theoretical calculations suggest antiferromagnetic coupling between the paramagnetic cobalt(II) ions and the radical ligands. Our study provides a rational design for stable organic radical-based ligands and further demonstrated the feasibility of a metal-radical approach toward magnetic materials.

The porous structure composed of non-metal elements of covalent organic frameworks (COFs) contributes to a large surface area and multifunction, rendering COFs a brilliant material for energy storage. Unfortunately, the low conductivity of most COFs limits their application in batteries. Herein, we fabricate COF-derived nitrogen-doped porous carbon (NPC) using nitrogen-rich COF-JLU2 as precursors by a simple carbonization for potassium-ion batteries (PIBs) and aluminum (Al) batteries for the first time. The computational results suggest that NPC has an enhanced conductivity and optimized electron density distribution. NPC could overcome the low conductivity of COF and thus further optimize its electrochemical performance in PIBs and Al batteries. It displays an excellent stability even after 2500 cycles (as the anode for PIBs) and 30000 cycles (as the cathode for Al batteries) with a high Coulombic efficiency. This fascinating study may be extended in other COFs for energy storage applications.

In this paper, a turbulence model based on OpenFOAM has been developed for the jet impingement heat transfer, which is based on the standard SST k-ω model and considers the effects of cross-diffusion term and the Kato-Launder model. The effects of the modifications have been studied for different nozzle-plate spacing of 4 and 9.2 in terms of pressure distributions, mean velocity, skin friction and the local Nusselt number distributions. The results have been compared with both the experimental data and the numerical results in the literatures. Good agreement is obtained in the studied cases and the developed model overcomes the false secondary Nusselt number peak in high nozzle-plate spacing for slot jets which is predicted by the standard SST k-ω model. The results show that the modifications improve the model’s ability to predict the heat transfer for jet impingement by reinforcing the model’s sensitivity to the pressure gradient. By way of comparative studies, it shows that the SST k-ω with transition model and the standard SST k-ω model are not sensitive to the pressure gradient. Meanwhile, the cases of nozzle-plate spacing of 2 and 6 are also investigated. This investigation indicates that the pressure gradient plays an important role for turbulent slot impinging jet. And it also reveals that the effect of cross-diffusion term should not be ignored in the boundary layer.

A novel ratiometric and reversible chemosensor 4-((2-(Benzo[d]thiazol-2-yl)phenyl)ethynyl)-N,N-diethylaniline (BT-1) based on ortho-arylethynyl benzothiazole with large Stokes shift (Δλ≈190 nm) was designed and synthesized to recognize Cu2+. Copper ion induces a remarkable fluorescence enhancement and causes formation of a BT-1-Cu complex. The clamp-on coordination mode of BT-1 to Cu2+ was demonstrated using Job's plot, mass spectrum (MS) and DFT calculations. The calculations also indicate that Cu2+ was chelated to BT-1 through N and alkyne instead of S and alkyne. The probe could quantify Cu2+ with the detection limit of 3.2 × 10−9 M. The in vitro imaging results indicated that the probe BT-1 was membrane-permeable and could be applied into the recognition of Cu2+ ions in living cells.

The classical synthesis of quinoids, which involves Takahashi coupling and subsequent oxidation, often gives only low to medium yields. Herein, we disclose the keto–enol-tautomerism-assisted spontaneous air oxidation of the coupling products to quinoids. This allows for the synthesis of various indandione-terminated quinoids in high isolated yields (85–95%). The origin of the high yield and the mechanism of the spontaneous air oxidation were ascertained by experiments and theoretical calculations. All the quinoidal compounds displayed unipolar n-type transport behavior, and single crystal field-effect transistors based on the micro-wires of a representative quinoid delivered an electron mobility of up to 0.53 cm2 V−1 s−1, showing the potential of this type of quinoid as an organic semiconductor., Facilitated by the highly efficient Pd-catalyzed coupling and keto–enol-tautomerism-assisted spontaneous air oxidation, various indandione-terminated quinoidal compounds have been synthesized in isolated yields up to 95%.

We investigate the evolution and interaction mechanism of different vortex structures for the jet in crossflow by a high precision numerical method. To verify the accuracy of the numerical method, the numerical and experimental results are compared. Numerical results show a reasonable agreement with the experimental data. The typical vortex structures can be clearly identified in the flow field, including shear layer vortices, horseshoe vortices, counter rotating vortices pairs, and wake vortices. Through the analysis of spatial distribution of different vortex structures, the formation and interaction mechanisms of different vortices are discussed in detail. The results show that the shear layer rolling up appears due to the strong rotation, inducing the formation of the shear layer vortices. The influences of velocity ratios on the vortex structures are further investigated. At low velocity ratios, the rotation is weak along the windward of the jet. With the increase in the velocity ratios, the stronger rotation is formed near the jet exit hole, inducing the instability of interface and formation of the shear layer vortices to occur earlier. In the far flow field, as the shear layer vortices gradually break up into the fine-scale vortices, both the rotation and shear tend to become weaker at different velocity ratios.

To investigate the impact of brash ice on the dynamics of the water exit of an axisymmetric vehicle, an experimental study was conducted on the water exit of an axisymmetric vehicle in brash ice using a water tank, launching system, control system, data acquisition system, and high-speed camera system. The brash ice zone was modeled using actual observational data from the Antarctic marginal ice zone off Wilkes Land in late winter. Brash ice was created from polypropylene material, and the influence of brash ice on the dynamics of the water-exit of the vehicle is analyzed. The results show that the collapse of bubbles during water-exit of a vehicle in the presence of brash ice creates a state of eruption, which splashes upward from the shoulder to the center of the vehicle, and the underwater cavities undergo shrinkage and shedding. The effects of brash ice on the magnitude of the force and moment on the vehicle during the process are diverse and operate in different directions. The overall deflection angle is greater than that under ice-free conditions. As water-exit speed increases, the splash time becomes earlier, and the extent of the splash becomes more dispersive. In addition, pressure falls as the vehicle approaches the water surface, and the extent and magnitude of pressure fluctuation during the whole water-exit process becomes more severe.

Open-shell π-conjugated compounds have recently received intense attention due to their unique properties and promising applications in materials science. However, the experiments on how the substituents affect their chemical bonding and structural motif remain less addressed. In this work, a series of tetrabenzo-Chichibabin's hydrocarbon (TBC) derivatives substituted by different electron-donating or -withdrawing groups at the termini were synthesized. The substituent effect was studied via X-ray crystallographic analysis. The strong electron-donating dimethylamino-group substituted TBC derivative underwent simultaneous oxidation to give two cyanine-like moieties at the termini. More interestingly, it exhibited unusual thermochromic and thermomagnetic behaviours.

The detection and identification of faults in rotary machines are of great significance to the mechanical equipment reliability especially the gearbox. Traditional machine learning algorithms suffer from low diagnosis accuracy of faults that have multiple types and exist concurrently. A novel machine learning method called hierarchical machine learning (HML) was proposed in this study to improve the faults diagnosis accuracy. The proposed algorithm consists of two layers. The first layer comprises a traditional machine learning model to identify the faults with distinguishable features and filter out these faults with indistinguishable features. The second layer model recognizes the faults filtered out by the first layer. In order to verify the effectiveness of the proposed method, the gearbox simulation experiment is carried out in the study. The simulation results validate that the proposed method outperforms other algorithms under an identical measure.

Despite the great potential of heteroatom-containing polycyclic aromatic hydrocarbons in organic optoelectronics, there are very limited reports on heteroaromatics containing a B–N–B bond in the π-scaffold. Herein, stable 1,9-dibora-9a-azaphenalenyl (DBAP) derivatives, named BNB-embedded phenalenyls, are presented. The DBAP skeleton contains a three-center two-π-electron B–N–B moiety with 12 π-electrons and can be regarded as the isoelectronic structure of the phenalenyl cation. Chemical reduction of the phenyl derivative of DBAP by potassium generated the dianion containing 14 delocalized π-electrons, which can be regarded as the isoelectronic structure of the phenalenyl anion. The dianion is sandwiched and stabilized by two bulky [K([18]crown-6)]+ counterions according to its X-ray structure. However, its monoanion (an isoelectronic structure of the henalenyl radical) generated by mixing equal moles of neutral compound and dianion gave an unusual B–N–B-embedded benzo[cd]fluoranthene dianion, which again...

Organic π-extended radicals display unique electronic structures, and could be used as promising functional materials. However, design and synthesis of stable radicals are challenging for chemists due to their high reactivity. In this work, we synthesized a stable N-annulated perylene-bridged bisphenoxyl diradicaloid, and its complex with Lewis acid boron trifluoride. Their ground-state geometric and electronic structures were systematically studied by various experimental methods, including X-ray crystallographic analysis, variable-temperature NMR spectroscopy, electron-spin resonance spectroscopy (ESR), and superconducting quantum interference device (SQUID) measurements, supported by density functional theory. Both were observed as open-shell singlet diradicaloids in the ground state. The bisphenoxyl diradicaloid demonstrated string features of strong near-infrared (NIR) absorption, closely packed π-dimer structure in crystals, amphoteric redox behavior with a small HOMO-LUMO energy band gap, and a rather small singlet-triplet gap, whereas the complex showed very different photophysical, electrochemical, and magnetic properties. Our studies provide an efficient method of making stable diradicaloids by Lewis acid/base complexation.

Most of the existing researches on public health events focus on the number and duration of events in a year or month, which are carried out by regression equation. COVID-19 epidemic, which was discovered in Wuhan, Hubei Province, quickly spread to the whole country, and then appeared as a global public health event. During the epidemic period, Chinese netizens inquired about the dynamics of COVID-19 epidemic through Baidu search platform, and learned about relevant epidemic prevention information. These groups’ search behavior data not only reflect people’s attention to COVID-19 epidemic, but also contain the stage characteristics and evolution trend of COVID-19 epidemic. Therefore, the time, space and attribute laws of propagation of COVID-19 epidemic can be discovered by deeply mining more information in the time series data of search behavior. In this study, it is found that transforming time series data into visibility network through the principle of visibility algorithm can dig more hidden information in time series data, which may help us fully understand the attention to COVID-19 epidemic in Chinese provinces and cities, and evaluate the deficiencies of early warning and prevention of major epidemics. What’s more, it will improve the ability to cope with public health crisis and social decision-making level.

A new class of pyridazine fused aromatics, 1,2-diazabenzo[ghi]perylenes, is conveniently synthesized from 2,7-dihydroxynaphthalene via intermolecular oxidative coupling followed by a condensation reaction. These new compounds are fully characterized via X-ray crystallographic analysis, optical spectroscopy and electrochemistry, in addition to DFT calculations. They show a twisted structure and unique P-/P- and M-/M-enantiomer pairs are observed in their single crystals. They exhibit intramolecular charge transfer character and emit at a longer wavelength with a larger Stokes shift compared with their all-carbon analog.

A novel ratiometric and reversible chemosensor 4-((2-(Benzo[d]thiazol-2-yl)phenyl)ethynyl)-N,N-diethylaniline (BT-1) based on ortho-arylethynyl benzothiazole with large Stokes shift (Δλ≈190 nm) was designed and synthesized to recognize Cu

We have prepared a turn-on fluorescent probe for biothiols based on bromoketo coumarin (KC-Br). The emission intensity of the coumarin chromophore is modulated by both the heavy atom effect and internal charge transfer (ICT) process. The probe KC-Br is intrinsically nonfluorescent; however, after being reacted with thiols, the bromide moiety is substituted by the -SH group, which elicits a significant fluorescence increase. We surmised the free -NH2 group would further react with carbonyl in the Cys/Hcy-substituted intermediate product yielding to Schiff base compound KC-Cys/KC-Hcy, but not in compound KC-GSH. The ICT effect has a stronger influence in compound KC-GSH than that in compound KC-Cys/KC-Hcy, resulting in compound KC-GSH having a stronger fluorescence. Thus, the probe has a good selectivity for GSH over other various biologically relevant species and even two other similar biothiols (Cys/Hcy) and could image glutathione (GSH) in living cells. We expect the design concept presented in this work would be widely used for the design of fluorescent probes for distinguishing among biothiols.

Hydrogen sulfide (H2S), traditionally considered to be a toxic gas with the typical smell of rotten eggs and an antioxidant or scavenger for reactive oxygen species (ROS) [1], has recently emerged as a member of the endogenous gaseous transmitter family of signaling molecules including nitric oxide (NO) and carbon monoxide (CO) [2–3]. The endogenous H2S is produced by the enzymes (such as cystathionine β-synthase, cyst a t h i o n i n e γ l y a s e , a n d 3 -me r c a p t o p y r u v a t e sulphurtransferase) catalysis action of cysteine or cysteine derivatives in mammalian tissues [4–6]. H2S plays an important physiological role in many biological processes, for instance, ischemia reperfusion injury, vasodilation, apoptosis, insulin signaling, and oxygen sensing [7–11]. However, abnormal levels of H2S is associated with various diseases, like Alzheimer’s disease [12], Down’s syndrome [13], diabetes [10], and liver cirrhosis [14]. Therefore, it’s very significant for monitoring H2S using sensitive, selective, and watersoluble fluorescent probe in the native biological environment. Fluorescence imaging has been widely used as a powerful tool for monitoring biomolecules within the context of living systems with high spatial and temporal resolution [15–16]. Naphthalimide dye is the favorable building block for constructing fluorescent probes because of its excellent photophysical properties, such as high extinction coefficients, excellent quantum yields, and great photostability. In addition, azido group is well-known for sensitively and selectively responding to H2S, the electron withdrawing azide is very easy reduced by H2S affording the electron donating amine [17–26]. Thus, in this work, we employed the naphthalimide chromophore as the signal reporter and azido group as the responding site for H2S to construct a H2S probe based on internal charge transfer (ICT) process (Scheme 1). In addition, to enhance the water solubility, we introduced a hydrophilic alcoholic group to the naphthalimide core. Prior to react with H2S, we supposed that probe Nap-N3 has negligible fluorescence. However, interaction of naphthalimide azide with H2S affords 4-amino-1,8-naphthalimide, which would elicit a significant fluorescence enhancement via ICT process caused by the electron donating amine and the electron withdrawing amide. So, probe Nap-N3 might be employed as a turn-on fluorescent probe for detecting H2S.

Heptamethine cyanines are favorable for fluorescence imaging applications in biological systems owing to their near-infrared (NIR) absorption and emission. However, it is very difficult to quench the fluorescence of NIR dyes by the classic photoinduced electron transfer mechanism due to their relatively high-lying occupied molecular orbital energy levels. Herein, we present a simple and effective “capping” approach to readily tune the fluorescence of NIR cyanines. The resulting new functional NIR CyBX (X = O, N, or S) dyes not only retain the intact tricarbocyanine scaffold, but also have a built-in switch to regulate the fluorescence by spiro-cyclization. When compared to traditional cyanines, novel CyBX dyes have a superior character in that their NIR optical properties can be readily tuned by the intrinsic spiro-cyclization mechanism. We expect that this “capping” strategy can be extended across not only the visual spectrum but also to structurally distinct fluorophores.

A key intermediate compound, 2,5,8,11-tetrabromo-1,6,7,12-tetrabutoxyperylene (Per-4Br), was synthesized from 3,6-dibromo-2,7-dioxylnaphthalene via simple regioselective oxidative radical–radical coupling, followed by reduction and nucleophilic substitution. Various bay- and ortho-octasubstituted perylenes containing cyano, methoxy and aryl groups were then obtained by nucleophilic substitution or Pd-catalyzed coupling reactions. X-ray crystallographic analyses reveal that these new perylene molecules process a twisted structure due to steric congestion at the bay-regions and there is no obvious intermolecular π–π interaction. As a result, they exhibit moderate fluorescence quantum yields even in solid state. Therefore, Per-4Br can serve as a versatile building block for various functional perylene dyes with tunable optoelectronic property.

The development of new functional fluorescent dyes has attracted great attention. Herein we have described a novel strategy to design a unique type of cyanine dyes by attaching two indolium moieties at the α-positions of the pyrrole core. The new type of cyanine dyes is named as PyCy fluorophores. Importantly, PyCy dyes can exhibit an exceptional feature, fluorescence turn-on response at pH varying from acidic to near-neutral conditions, and a ratiometric fluorescence response at pH varying from near-neutral to basic conditions. By taking advantage of the fluorescence turn-on response of PyCy2 at pH varying from acidic to near-neutral conditions and emission properties of PyCy2, we have demonstrated that a small-molecule fluorescent probe can image pH variations in living cells. Furthermore, we have demonstrated that PyCy2 can sense real-time pH changes under alkaline conditions induced by enzymes based on the ratiometric fluorescence response of PyCy2 at pH varying from near-neutral to basic conditions. We expect that the new design strategy for PyCy fluorophores may prompt the development of a wide variety of cyanine derivatives with desirable properties.

The main purpose of this study was to investigate the influence of air-injection technique on unsteady cloud cavitating flow dynamics. High-speed camera and pressure measurement system are used to record ventilated cavitation images and wall-pressure fluctuation in a convergent–divergent channel, respectively. The measured ventilated cavitation evolution process and corresponding wall-pressure fluctuation are compared with those obtained under non-ventilation condition. The results show that air-injection technique can significantly suppress pressure pulses induced by cavity collapse. Furthermore, by increasing ventilation rate, the time evolution of cavitation tends to be more stable, the wall-pressure fluctuation magnitude is reduced significantly, and the cloud shedding frequency is reduced, which is believed to be related to the interaction between injected air and re-entrant flow.

Broadband capturing and FRET-based light-harvesting molecular triads, CRBs, based on the coumarin-rhodamine-BODIPY platform were rationally designed and synthesized. The absorption band of CRBs starts from blue-green to yellow-orange regions (330-610 nm), covering the strong radiation scope of sunlight. The peripheral coumarin and BODIPY chromophore energy could transfer to the central acceptor rhodamine by a one-step direct way. The energy of the coumarin moiety could also transfer to the BODIPY unit, subsequently transferring to the rhodamine core by two-step sequential ways. Both the efficiencies of the coumarin moiety and the BODIPY unit to the rhodamine core in CRBs, determined by two different ways, are very high.

We introduce a new FRET strategy to construct a ratiometric fluorescent H2S sensor. The ratio emission signal of the coumarin–naphthalimide dyad is modulated by the FRET process, which works in coordination with the ICT mechanism. The FRET process on/off is controlled through tuning the overlap level of the donor emission spectrum with the acceptor absorption via modulation of the acceptor fluorophore absorption wavelength. CN-N3 was applied to visualize both the intracellular exogenous and endogenous H2S through blue and green emission channels.