Highly conducting single-molecule topological insulators based on mono- and di-radical cations

Single-molecule topological insulators are promising candidates as conducting wires over nanometre length scales. A key advantage is their ability to exhibit quasi-metallic transport, in contrast to conjugated molecular wires which typically exhibit a low conductance that decays as the wire length increases. Here, we study a family of oligophenylene-bridged bis(triarylamines) with tunable and stable mono- or di-radicaloid character. These wires can undergo one- and two-electron chemical oxidations to the corresponding mono-cation and di-cation, respectively. We show that the oxidized wires exhibit reversed conductance decay with increasing length, consistent with the expectation for Su–Schrieffer–Heeger-type one-dimensional topological insulators. The 2.6-nm-long di-cation reported here displays a conductance greater than 0.1G0, where G0 is the conductance quantum, a factor of 5,400 greater than the neutral form. The observed conductance–length relationship is similar between the mono-cation and di-cation series. Density functional theory calculations elucidate how the frontier orbitals and delocalization of radicals facilitate the observed non-classical quasi-metallic behaviour

Competition modes determine ecosystem stability in rock–paper–scissors games

Identification of the mechanisms which permit ecological communities to maintain high levels of biodiversity is of both theoretical interest and practical importance. Intransitive competition, in which there is no single superior competitor, is known to play an important role in this problem. In this study, we undertake a systematic comparative analysis of how different competition modes and ranges affect community stability in paper-rock-scissors games. We confirm that short-ranged interactions, in combination with cyclic competition, permits relatively stable coexistence. However, in contrast to previous studies, we show that long-range interactions can also produce stable communities. This stability emerges when competition interactions create asymmetries in the opportunities for population growth depending on the abundance of the species. Our findings demonstrate that small differences in the way species compete can qualitatively change dynamic behaviors of the system, and therefore emphasize the importance of correctly identifying these competition modes when designing conservation actions

Contrasting effects of dispersal network heterogeneity on ecosystem stability in rock-paper-scissors games

Intransitive competition, typically represented by the classic rock-paper-scissors game, provides an endogenous mechanism promoting species coexistence. As well known, species dispersal and interaction in nature might occur on complex patch networks, with species interacting in diverse ways. However, the effects of different interaction modes, combined with spatial heterogeneity in patch connectivities, have not been well integrated into our general understanding of how stable coexistence emerges in cyclic competition. We thus incorporate network heterogeneity into the classic rock-paper-scissors game, in order to compare ecosystem stability under two typical modes of interaction: species compete to fill empty sites, and species seize each other’s colony sites. On lattice-structured regular networks, the two interaction modes produce similar stability patterns through forming conspecific clusters to reduce interspecific competition. However, for heterogeneous networks, the interaction modes have contrasting effects on ecosystem stability. Specifically, if species compete for colony sites, increasing network heterogeneity stabilizes competitive dynamics. When species compete to fill empty sites, an increase in network heterogeneity leads to larger population fluctuations and therefore a higher risk of stochastic extinctions, in stark contrast to current knowledge. Our findings strongly suggest that particular attention should be devoted to testing which mode of interaction is more appropriate for modelling a given system

Effects of the Peripheral Heteroaryl Substituents on the Photochromism of New Pyridine-Containing Diarylethenes

Three new unsymmetrical pyridine-containing diarylethenes with a variable peripheral heteroaryl unit were synthesized and their structures were determined by single-crystal X-ray diffraction analysis. The substituent effects of variable heteroaryl groups on the photochromic and fluorescence properties were systematically discussed. Thienyl and thiazyl could effectively enhance the cyclization quantum yields and photoconversion ratios in the photostationary state, as compared to the phenyl group. However, they had no obvious effect on the fluorescence behaviors. Moreover, X-ray structural analysis revealed that the N···S heteroatom-contact interactions resulted in a higher cyclization quantum yield, which may be ascribed to the effective stabilizing ability on the photoreactive formations in diarylethenes with a thienyl/thiazyl unit

Towards a mechanistic understanding of variation in aquatic food chain length

Ecologists have long sought to understand variation in food chain length (FCL) 42 among natural ecosystems. Various drivers of FCL, including ecosystem size, 43 resource productivity and disturbance, have been hypothesized. However, when 44 results are aggregated across existing empirical studies from aquatic ecosystems, we 45 observe mixed FCL responses to these drivers. To understand this variability, we 46 develop a unified competition-colonization framework for complex food webs 47 incorporating all of these drivers. With competition-colonization tradeoffs among 48 basal species, our model predicts that increasing ecosystem size generally results in a 49 monotonic increase in FCL, while FCL displays non-linear, oscillatory responses to 50 resource productivity or disturbance in large ecosystems featuring little disturbance or 51 high productivity. Interestingly, such complex responses mirror patterns in empirical 52 data. Therefore, this study offers a novel mechanistic explanation for observed 53 variations in aquatic FCL driven by multiple environmental factors

The Appropriate Combination of Hemagglutinin and Neuraminidase Prompts the Predominant H5N6 Highly Pathogenic Avian Influenza Virus in Birds

Haemagglutinin (HA) and neuraminidase (NA) are two vital surface glycoproteins of influenza virus. The HA of H5N6 highly pathogenic avian influenza virus is divided into Major/H5 and Minor/H5, and its NA consists of short stalk NA and full-length stalk NA. The strain combined with Major/H5 and short stalk NA account for 76.8% of all strains, and the proportion was 23.0% matched by Minor/H5 and full-length stalk NA. Our objective was to investigate the influence of HA–NA matching on the biological characteristics and the effects of the epidemic trend of H5N6 on mice and chickens. Four different strains combined with two HAs and two NAs of the represented H5N6 viruses with the fixed six internal segments were rescued and analyzed. Plaque formation, NA activity of infectious particles, and virus growth curve assays, as well as a saliva acid receptor experiment, with mice and chickens were performed. We found that all the strains can replicate well on Madin–Darby canine kidney (MDCK) cells and chicken embryo fibroblasts (CEF) cells, simultaneously, mice and infection group chickens were complete lethal. However, the strain combined with Major/H5 and short stalk N6 formed smaller plaque on MDCK, showed a moderate replication ability in both MDCK and CEF, and exhibited a higher survival rate among the contact group of chickens. Conversely, strains with opposite biological characters which combined with Minor/H5 and short stalk N6 seldom exist in nature. Hence, we drew the conclusion that the appropriate combination of Major/H5 and short stalk N6 occur widely in nature with appropriate biological characteristics for the proliferation and transmission, whereas other combinations of HA and NA had a low proportion and even have not yet been detected

Highly Emissive 9‐Borafluorene Derivatives: Synthesis, Photophysical Properties and Device Fabrication

A series of 9-borafluorene derivatives, functionalised with electron-donating groups, have been prepared. Some of these 9-borafluorene compounds exhibit strong yellowish emission in solution and in the solid state with relatively high quantum yields (up to 73.6 % for FMesB-Cz as a neat film). The results suggest that the highly twisted donor groups suppress charge transfer, but the intrinsic photophysical properties of the 9-borafluorene systems remain. The new compounds showed enhanced stability towards the atmosphere, and exhibited excellent thermal stability, revealing their potential for application in materials science. Organic light-emitting diode (OLED) devices were fabricated with two of the highly emissive compounds, and they exhibited strong yellow-greenish electroluminescence, with a maximum luminance intensity of >22 000 cd m$^{-2}$. These are the first two examples of 9-borafluorene derivatives being used as light-emitting materials in OLED devices, and they have enabled us to achieve a balance between maintaining their intrinsic properties while improving their stability

Highly Emissive 9-Borafluorene Derivatives: Synthesis, Photophysical Properties and Device Fabrication

A series of 9-borafluorene derivatives, functionalised with electron-donating groups, have been prepared. Some of these 9-borafluorene compounds exhibit strong yellowish emission in solution and in the solid state with relatively high quantum yields (up to 73.6 % for FMesB-Cz as a neat film). The results suggest that the highly twisted donor groups suppress charge transfer, but the intrinsic photophysical properties of the 9-borafluorene systems remain. The new compounds showed enhanced stability towards the atmosphere, and exhibited excellent thermal stability, revealing their potential for application in materials science. Organic light-emitting diode (OLED) devices were fabricated with two of the highly emissive compounds, and they exhibited strong yellow-greenish electroluminescence, with a maximum luminance intensity of >22 000 cd m$^{-2}$. These are the first two examples of 9-borafluorene derivatives being used as light-emitting materials in OLED devices, and they have enabled us to achieve a balance between maintaining their intrinsic properties while improving their stability