Thickness-dependent exciton relaxation dynamics of few-layer rhenium diselenide

Rhenium diselenide(ReSe_(2))has gathered much attention due to its low symmetry of lattice structure,which makes it possess in-plane anisotropic optical,electrical as well as excitonic properties and further enables ReSe_(2)have an important application in optoelectronic devices.Here,we report the thickness-dependent exciton relaxation dynamics of mechanically exfoliated few-layer ReSe_(2)flakes by using time-resolved pump–probe transient transmission spectroscopies.The results reveal two thickness-dependent relaxation processes of the excitons.The fast one correlates with the exciton formation(i.e.,the conversion of hot carriers to excitons),while the slow one is attributed to the exciton recombination dominated by defect-assisted exciton trapping besides photon emission channel.The decrease of scattering probability caused by defects leads to the increase of fast lifetime with thickness,and the increase of slow lifetime with thickness is related to the trap-mediated exciton depopulation induced by surface defects.Polarization-dependent transient spectroscopy indicates the isotropic exciton dynamics in the two-dimensional(2D)plane.These results are insightful for better understanding of excitonic dynamics of ReSe_(2)materials and its application in future optoelectronic and electronic devices.

Glutathione peroxidase mimicry of diphenyl diselenide: Plausible contribution of proteins’ thiols

Organoseleniums are a class of compounds attracting attention across the globe owing to their Glutathione peroxidase(GPx)mimicry,which confers on them a strong antioxidant activity.Diphenyl diselenide(DPDS)is an Organoselenium whose GPx mimetic property has been suggested to rely on the oxidation of non-protein or protein thiols critical to the activities of some sulfhydryl enzymes.This study,therefore investigated the GPx mimic/antioxidant property of DPDS as well as the role of thiols of two key sulfhydryl enzymes,cerebral Na^(+)/K^(+)-ATPase(sodium pump)and hepatic delta-aminolevulinic acid dehydratase(δ-ALAD)in the GPx mimicry of DPDS.Albino Wistar rats were euthanized,and the liver and brain were removed and used to assay for the effect of DPDS on lipid peroxidation induced by two prooxidants[Fe2^(+)(10μM)and H2O2,(1 mM)]as well as the activities of the sulfhydryl enzymes.The results revealed that DPDS profoundly(P<0.05)counteracted Fe2^(+)and H2O2-induced lipid peroxidation in the rats’hepatic and cerebral tissues.Furthermore,the results of assay systems for lipid peroxidation and sodium pump revealed that DPDS inhibited Na^(+)/K^(+)-ATPase and lipid peroxidation in the brain tissue homogenates in the same reaction system.A similar result was obtained in the assay system for lipid peroxidation and hepaticδ-ALAD as DPDS simultaneously inhibited the enzyme’s activity and lipid peroxidation.This suggests that the GPx mimetic property of DPDS may be linked to the enzymes’loss of activity,which further validates the suggestions that the enzymes’inhibition,as well as the antioxidant action of DPDS,rely on the oxidation of critical thiols of the enzymes.However,the GPx mimicry of DPDS should be investigated in the presence of thiol-blocking or oxidizing agents in biological systems in order to further ascertain the role of protein thiols.

Electrospinning of Flexible Poly(vinyl alcohol)/MXene Nanofiber-Based Humidity Sensor Self-Powered by Monolayer Molybdenum Diselenide Piezoelectric Nanogenerator

Two-dimensional material has been widely investigated for potential applications in sensor and flexible electronics.In this work,a self-powered flexible humidity sensing device based on poly(vinyl alcohol)/Ti_(3)C_(2)Tx(PVA/MXene)nanofibers film and monolayer molybdenum diselenide(MoSe2)piezoelectric nanogenerator(PENG)was reported for the first time.The monolayer MoSe_(2)-based PENG was fabricated by atmospheric pressure chemical vapor deposition techniques,which can generate a peak output of 35 mV and a power density of42 mW m^(-2).The flexible PENG integrated on polyethylene terephthalate(PET)substrate can harvest energy generated by different parts of human body and exhibit great application prospects in wearable devices.The electrospinned PVA/MXene nanofiber-based humidity sensor with flexible PET substrate under the driven of monolayer MoSe_(2) PENG,shows high response of~40,fast response/recovery time of 0.9/6.3 s,low hysteresis of 1.8%and excellent repeatability.The self-powered flexible humidity sensor yields the capability of detecting human skin moisture and ambient humidity.This work provides a pathway to explore the high-performance humidity sensor integrated with PENG for the self-powered flexible electronic devices.

Applications of 2D-Layered Palladium Diselenide and Its van der Waals Heterostructures in Electronics and Optoelectronics

The rapid development of two-dimensional(2D)transition-metal dichalcogenides has been possible owing to their special structures and remarkable properties.In particular,palladium diselenide(PdSe_(2))with a novel pentagonal structure and unique physical characteristics have recently attracted extensive research inter-est.Consequently,tremendous research progress has been achieved regarding the physics,chemistry,and electronics of PdSe_(2).Accordingly,in this review,we recapitulate and summarize the most recent research on PdSe_(2),including its structure,properties,synthesis,and appli-cations.First,a mechanical exfoliation method to obtain PdSe_(2) nanosheets is introduced,and large-area synthesis strate-gies are explained with respect to chemical vapor deposition and metal selenization.Next,the electronic and optoelectronic properties of PdSe_(2) and related hetero-structures,such as field-effect transistors,photodetectors,sensors,and thermoelec-tric devices,are discussed.Subsequently,the integration of systems into infrared image sensors on the basis of PdSe_(2) van der Waals heterostructures is explored.Finally,future opportunities are highlighted to serve as a general guide for physicists,chemists,materials scientists,and engineers.Therefore,this com-prehensive review may shed light on the research conducted by the 2D material community.

Small changes in the length of diselenide bond-containing linkages exert great influences on the antitumor activity of docetaxel homodimeric prodrug nanoassemblies

Homodimeric prodrug-based self-assembled nanoparticles,with carrier-free structure and ultrahigh drug loading,is drawing more and more attentions.Homodimeric prodrugs are composed of two drug molecules and a pivotal linkage.The influence of the linkages on the self-assembly,in vivo fate and antitumor activity of homodimeric prodrugs is the focus of research.Herein,three docetaxel(DTX)homodimeric prodrugs are developed using different lengths of diselenide bond-containing linkages.Interestingly,compared with the other two linkages,the longest diselenide bond-containing linkage could facilitate the self-delivery of DTX prodrugs,thus improving the stability,circulation time and tumor targeting of prodrug nanoassemblies.Besides,the extension of linkages reduces the redox-triggered drug release and cytotoxicity of prodrug nanoassemblies in tumor cells.Although the longest diselenide bond-containing prodrug nanoassemblies possessed the lowest cytotoxicity to 4T1 cells,their stable nanostructure maintained intact during circulation and achieve the maximum accumulation of DTX in tumor cells,which finally“turned the table”.Our study illustrates the crucial role of linkages in homodimeric prodrugs,and gives valuable proposal for the development of advanced nano-DDS for cancer treatment.

Two‑Dimensional Platinum Diselenide:Synthesis,Emerging Applications,and Future Challenges

In recent years,emerging two-dimensional(2D)platinum diselenide(PtSe2)has quickly attracted the attention of the research community due to its novel physical and chemical properties.For the past few years,increasing research achievements on 2D PtSe2 have been reported toward the fundamental science and various potential applications of PtSe2.In this review,the properties and structure characteristics of 2D PtSe2 are discussed at first.Then,the recent advances in synthesis of PtSe2 as well as their applications are reviewed.At last,potential perspectives in exploring the application of 2D PtSe2 are reviewed.

Morphology-controlled Tantalum Diselenide Structures as Self-optimizing Hydrogen Evolution Catalysts

Metallic layered transition metal dichalcogenides(TMDs)nanomaterials based on Group 5 transition metals are attracting substantial interests as alternative catalysts for hydrogen evolution reaction(HER).However,controllable preparation of tantalum diselenide(TaSe2)remains challenging,which has hindered the exploration on its application in HER.Herein,we develop a facile method named surface-assisted chemical vapor transport(SACVT)for controllable synthesis of TaSe2 plates and nanobelts,by regulating the molar ratio of selenium to tantalum and reaction temperature.Unique quasi-arrays and self-supported structure help TaSe2 nanobelt own more active sites and higher ability of charge transfer,so it is superior to TaSe2 plate in electrocatalytic HER.Interestingly,they both exhibit the ability to optimize their morphologies upon cycling for dramatically improved and robust electrocatalytic performance.The selfoptimized structures can increase the effective active surface by exposing more active sites on the basal-planes and edges,shorten the interlayer electron-transfer pathways at a thinned domain,and accelerate the charge transfer,which mainly derive from high basal-plane activity and weak interaction between layers of metallic TaSe2.This work provides a reliable way for controllable synthesis of different TaSe2 structures,motivating further efforts to explore new high-efficiency catalysts in the large family of metallic TMDs for electrochemical energy conversion.

Tunable Electronic and Magnetic Properties from Structure Phase Transition of Layered Vanadium Diselenide

The atomic geometry, structure stability, electronic and magnetic properties of VSe2 were systematically investigated based on the density functional theory（DFT）. Varying from 3D to 2D four VSe2 structures, bulk 2H-VSe2 and 1T-VSe2, monolayer H-VSe2 and T-VSe2 are all demonstrated as thermodynamically stable by lattice dynamic calculations. More interestingly, the phase transition temperature is dramatically different due to the lattice size. Finally, owing to different crystal structures, H-VSe2 is semimetallic whereas T-VSe2 is totally metallic and also they have different magnetic moments. Our main argument is that being exfoliated from bulk to monolayer, 2H-VSe2 transforms to T-VSe2, accompanied by both semimetallic-metallic transition and dramatic magnetic moment variation. Our calculations provide a novel structure phase transition and an efficient way to modulate the electronic structure and magnetic moment of layered VSe2, which suggests potential applications as high-performance functional nanomaterial.

A convenient and stereoselective synthesis of (Z)-allyl selenides via Sm/TMSCl system-promoted coupling of Baylis-Hillman adducts with diselenides

A simple and convenient procedure for stercoselective synthesis of （Z）-allyl selenides has been developed by a one-pot reaction of diselenides with Baylis-Hillman adducts in the presence of samarium metal-trimethylsilyl chloride under mild conditions. Presumably, the diselenides are cleaved by Sm/TMSCI system to form selemde anions, which then undergo SN2＇ substitution of Baylis-Hillman adducts to produce the （Z）-allyl selenides.

Zn/ ZrCl_4 System Induced Reductive Cleavage of Se-Se Bond in Diaryl Diselenides: A Novel Method for the Systhesis of Selenoesters

The Se-Se bond in diaryl diselenides was reduced by Zn/ZrCl4 system to produce selenide anions, which react with acyl chlorides or acid anhydrides to afford selenoesters in THF under mild and neutral conditions.

The Synthesis of Bis(carboxyalkylmethyl) Diselenides by Selenium Transfer Reaction of Aryl Selenoamides

Aryl selenoamides react smoothly with a-haloacetic acid in various alcohol to give corresponding bis(carboxyalkylmethyl) diselenides in good yields.

Samarium Diiodide-Mediated Reductive Cleavage of Se-Se Bond of Diacyl Diselenides:A New Method for Synthesis of β-Selenoesters

The reduction of diacyl diselenides by samarium diiodide led to the production ofsamarium acylselenolates, which reacted with a,β-unsaturated esters or nitriles to give β-selenoesters or selenonitriles under mild and neutral conditions.

Synthesis of α-Selenoesters By Reactions of α-Bromoesters With Diselenides Promoted By Metallic Tin

α-Bromoesters can react with diselenides by metallic tin in THF to give α-selenoesters in moderate to good yields.

Dynamic diselenide bond-enabled liquid crystal elastomer-based two-way shape memory aerogels with weldability and closedloop recyclability

Two-way shape memory polymeric aerogels(2W-SMPAs),with the ability to undergo reversible shape deformation in response to external stimuli,have extensive application in diverse fields such as actuators,sensors,robotics,and other relevant domains.In this study,we introduce a novel approach for fabricating a 2W-SMPA material based on liquid crystal elastomers(LCEs)incorporating dynamic diselenide bonds.The aerogel exhibits liquid crystal phases,excellent compressibility and shape stability,and the mesogens are uniaxial-oriented along the stretching direction.By capitalizing on the dynamic diselenide bonds,the LCEbased aerogel demonstrated remarkable reprogrammability,weldability,and recyclability through thermal reorganization.The shape-programmed aerogel sample exhibits reversible shrinking deformation during the heating and cooling cycles,ultimately achieving a maximum shrinkage ratio of 26.1%.Moreover,the LCE-based aerogel's porous structure and monodomain orientation effectively enable the adsorption of the photothermal dye DR1 and facilitated the reversible photothermal-induced shape deformation when exposed to 520 nm light irradiation.These findings reveal the potential application of this innovative LCE-based aerogel material,enabled by dynamic diselenide bonds,in various areas including control devices,soft actuators,and other diverse fields.

Room-temperature vertical ferroelectricity in rhenium diselenide induced by interlayer sliding

One variety of ferroelectricity that results from lateral relative movements between the adjacent atomic layers is referred to as sliding ferroelectricity,which generates an interfacial charge transfer and hence a polarization reversal.The mechanism of sliding ferroelectricity existent in van der Waals crystals is quite distinct from the conventional ferroelectric switching mechanisms mediated by ion displacement.It creates new possibilities for the design of two-dimensional(2D)ferroelectrics since it can be achieved even in non-polar systems.Before 2D ferroelectrics can be widely employed for practical implementations,however,there is still significant work to be done on several fronts,such as exploring ferroelectricity possibly in more potential 2D systems.Here,we report the experimental observation of room-temperature robust vertical ferroelectricity in layered semiconducting rhenium diselenide(ReSe_(2)),a representative member of the transition metal dichalcogenides material family,based on a combined research of nanoscale piezoresponse and second harmonic generation measurements.While no such ferroelectric behavior was seen in 1L ReSe_(2),2L ReSe_(2)exhibits vertical ferroelectricity at ambient environment.Based on density-functional theory calculations,we deduce that the microscopic origin of ferroelectricity for ReSe_(2)is uncompensated vertical charge transfer that is dependent on in-plane translation and switchable upon interlayer sliding.Our findings have important ramifications for the ongoing development of sliding ferroelectricity since the semiconducting properties and low switching barrier of ReSe2 open up the fascinating potential for functional nanoelectronics applications.

Diselenide as a Dual Functional Mechanophore Capable of Stress Self-Reporting and Self-Strengthening in Polyurethane Elastomers

Unlike biological materials that can sense mechanical force and actively remodel locally,synthetic polymers typically break down under stress.Molecular-level responses to damage with both stress-reporting and self-strengthening functions are significant yet difficult to realize for synthetic polymers.To overcome this challenge,chemo-mechanical coupling into polymers that can simultaneously ameliorate mechanical,optical,or other functional properties of a polymer combined with mechanical treatment will offer a new principle for materials design.Here,we report a kind of elastomer in which destructive forces are channelled into productive and bond-forming reactions by using diselenide(Se–Se)as a mechanophore.Polyurethane has been functionalized with labile Se–Se bonds,whosemechanical activation generates seleno radicals that trigger radical transfer and cross-linking reactions in situ.These reactions are activated efficiently in a mechanical way by compression in bulk materials.The resulting covalent networks possess turn-on mechano-fluorescence and increased moduli,which provide the functions of stress reporting,mechano-healing,and mechano-remodeling for the deformed film.This study not only illuminates themechano-responsive nature of Se–Se bonds in the bulk state but also paves the way for the development of new stress-responsive materials.

Halide vapor phase epitaxy of monolayer molybdenum diselenide single crystals

Single-crystalline transition metal dichalcogenides(TMD)films are of potential application in future electronics and optoelectronics.In this work,a halide vapor phase epitaxy(HVPE)strategy was proposed and demonstrated for the epitaxy of molybdenum diselenide(MoSe_(2))single crystals,in which metal halide vapors were in-situ produced by the chlorination of molybdenum as sources for the TMD growth.Combined with the epitaxial sapphire substrate,unidirectional domain alignment was successfully achieved and monolayer single-crystal MoSe_(2) films have been demonstrated on a 2-inch wafer for the first time.A series of characterizations ranging from centimeter to nanometer scales have been implemented to demonstrate the high quality and uniformity of the MoSe_(2).This work provides a universal strategy for the growth of TMD single-crystal films.

Electrochemical radical annulation of 2-alkynyl biaryls with diselenides under catalyst-and chemical oxidant-free conditions

A facile and efficient electrochemical method for sustainable constructing both selanyl phenanthrenes and selanyl polycyclic heteroaromatics(32 examples,71%-97%yields)through the radical annulation of 2-alkynyl biaryls and 2-heteroaryl-substituted alkynyl benzenes with diselenides at ambient temperature under additive-,chemical oxidant-,catalyst-free and mild conditions was established.

Visible-to-near-infrared photodetectors based on SnS/SnSe_(2)and SnSe/SnSe_(2)p−n heterostructures with a fast response speed and high normalized detectivity

The emergent two-dimensional(2D)material,tin diselenide(SnSe_(2)),has garnered significant consideration for its potential in image capturing systems,optical communication,and optoelectronic memory.Nevertheless,SnSe_(2)-based photodetection faces obstacles,including slow response speed and low normalized detectivity.In this work,photodetectors based on SnS/SnSe_(2)and SnSe/SnSe_(2)p−n heterostructures have been implemented through a polydimethylsiloxane(PDMS)−assisted transfer method.These photodetectors demonstrate broad-spectrum photoresponse within the 405 to 850 nm wavelength range.The photodetector based on the SnS/SnSe_(2)heterostructure exhibits a significant responsivity of 4.99×10^(3)A∙W^(−1),normalized detectivity of 5.80×10^(12)cm∙Hz^(1/2)∙W^(−1),and fast response time of 3.13 ms,respectively,owing to the built-in electric field.Meanwhile,the highest values of responsivity,normalized detectivity,and response time for the photodetector based on the SnSe/SnSe_(2)heterostructure are 5.91×10^(3)A∙W^(−1),7.03×10^(12)cm∙Hz^(1/2)∙W−1,and 4.74 ms,respectively.And their photodetection performances transcend those of photodetectors based on individual SnSe_(2),SnS,SnSe,and other commonly used 2D materials.Our work has demonstrated an effective strategy to improve the performance of SnSe_(2)-based photodetectors and paves the way for their future commercialization.

Interlayer interactions in anisotropic atomically thin rhenium diselenide

In this work, we study the interlayer phonon vibration modes, the layer-number- dependent optical bandgap, and the anisotropic photoluminescence （PL） spectra of atomically thin rhenium diselenide （ReSe2） for the first time. The ultralow frequency interlayer Raman spectra and the polarization-resolved high frequency Raman spectra in ReSe2 allow the identification of its layer number and crystal orientation. Furthermore, PL measurements show the anisotropic optical emission intensity of the material with its bandgap increasing from 1.26 eV in the bulk to 1.32 eV in the monolayer. The study of the layer-number dependence of the Raman modes and the PL spectra reveals relatively weak van der Waal＇s interaction and two-dimensional （2D） quantum confinement in the atomically thin ReSe2. The experimental observation of the intriguing anisotropic interlayer interaction and tunable optical transition in monolayer and multilayer ReSe2 establishes the foundation for further exploration of this material in the development of anisotropic optoelectronic devices functioning in the near-infrared spectrum, which is important for many applications in optical communication and infrared sensing,