Hyperbranched polytriazoles with spring-like architectures exhibit the feature of aggregation-induced emission (AIE) due to the high compressibility of polymer spheres from solution to aggregate. Thanks to their AIE effect, the polymer nanoaggregates can detect explosives with superamplification effect.
Liquid-crystalline and light-emitting poly(2-alkyne)s and poly(1-phenyl-1-alkyne)s containing biphenyl (Biph) cores, alkyl spacers, and alkoxy tails (-{RC=C[(CH2)m-OCO-Biph-OC7H15]}n-, where R, m = CH3, 4 [P1(4)]; CH3, 9 [P1(9)]; C6H5, 4 [P2(4)]; and C6H5, 9 [P2(9)]}, were synthesized and the effects of the spacer length and backbone structure on the properties of the polymers were investigated. The disubstituted acetylene monomers [1(m) and 2(m) (m = 4, 9)] were prepared by esterification of biphenylcarboxylic acid (6) with ω-alkynyl alcohols [4(m) or 5(m)]. Polymerizations of 1(m) and 2(m) were effected by WCl6−, MoCl5−, and NbCl5−Ph4Sn and the reactions catalyzed by WCl6−Ph4Sn under optimal conditions produce polymers P1(m) and P2(m) with high molecular weights (Mw up to 3.1 × 105) in good yields (up to 81%). The structures and properties of the disubstituted polyacetylenes were characterized and evaluated by nuclear magnetic resonance (NMR), thermogravimetry (TGA), differential scanning calorimetry (DSC), polarized optical microscope (POM), X-ray diffraction (XRD), ultraviolet spectroscopy (UV), and photoluminescence (PL) analyses. The polymers are resistant to thermolysis (Td ≥ 360 °C) and all but P2(4) exhibit liquid crystallinity at elevated temperatures. The polymers with long methylene spacers, that is, P1(9) and P2(9), form a smectic A (SmA) mesophase with a monolayer arrangement. Upon excitation, strong UV and blue emissions peaking at 369 and 460 nm are observed in P1(m) and P2(m), respectively, whose quantum yields are found to increase with the spacer lengths.
Blue light‐emitting poly(1‐phenyl‐1‐alkyne)s containing photo‐cross‐linkable vinyl pendants were synthesized and photophysically characterized. Photoluminescence quantum yields are virtually unchanged for pristine and photo‐cross‐linked films showing excellent stability and light emitting property of the insoluble polymer film after photo‐cross‐linking process. By using laser interference lithography technique, active submicron two‐dimensional photonic crystal structures have been fabricated by exposure to UV light. The obtained high quality nanostructures demonstrate that these polymers are applicable in active photonic devices such as polymer light emitting diode or distributed feedback lasers.
We report the design and fabrication of a vertical structure using a distributed Bragg reflector and dielectric material layer to achieve optimized optical absorption enhancement for a stack of monolayer WS2 and MoS2, namely, a tenfold increase in absorption over a 100 nm spectral range. Our research indicates that we can approach over 50% absorption by finely tuning the thickness of the spacer layer. Our theoretical model shows that the dependence of the absorption coefficient on the spacer thickness can be understood as a solution of a non-Hermitian Schrödinger equation. These results advance the development of broadband optical devices, including solar energy conversion and sensitive optical sensors, by using two-dimensional excitonic materials.
In this paper, four new π-conjugated dendrimers G1 and G2-1–G2-3, constructed by triphenylamine and carbazole moieties, have been successfully prepared via a simple synthetic route. This molecular design imparts the materials with good solution-processability, high thermal and morphological stabilities, and low oxidation potential, all of which are promising properties for optoelectronic materials. The double-layer OLEDs fabricated using these materials through solution processing demonstrate that they can exhibit dual functions, hole-transporting and light-emitting. Devices using G1 or G2-1 as the hole-transporting layer present good stability during the passage of current, with a maximum efficiency of 1.70 and 1.59 cd A−1, respectively. Moreover, devices using these dendrimers as the emitting layer show moderate performance, and the device of G2-2 gives a maximum luminance and efficiency of 1190 cd m−2 and 1.67 cd A−1, respectively, thanks to three-dimensional building of the dendritic system, which might suppress the inherent reductive or aggregation-caused quenching that usually happens for triphenylamine/carbazole derivatives to some degree. Also, the photo-cross-linking property of triple bonds enables ready fabrication of highly fluorescent photoresist patterns of these dendrimers.
Moiré superlattices have emerged as a highly controllable quantum platform for exploration of various fascinating phenomena, such as Mott insulator states, ferroelectric order, unconventional superconductivity and orbital ferromagnetism. Although remarkable progress has been achieved, current research in moiré physics has mainly focused on the single species properties, while the coupling between distinct moiré quantum phenomena remains elusive. Here we demonstrate, for the first time, the strong coupling between ferroelectricity and correlated states in a twisted quadrilayer MoS 2 moiré superlattice, where the twist angles are controlled in sequence to be ∼ 57°, ∼ 0°, and ∼ –57°. Correlated insulator states are unambiguously established at moiré band filling factors v = 1, 2, 3 of twisted quadrilayer MoS 2 . Remarkably, ferroelectric order can occur at correlated insulator states and disappears quickly as the moiré band filling deviates from the integer fillings, providing smoking gun evidences of the coupling between ferroelectricity and correlated states. Our results demonstrate the coupling between different moiré quantum properties and will hold great promise for new moiré physics and applications.
Istitut di Statistica Medica e Biometria, Universita di Milano Istitut di Ricerche Farmacologische 'Mario Negri', Via Eritrea 62, 20157 Milan, Italy
Bi-layer non-doped white organic light-emitting diodes (WOLEDs) with hole-transporting layer 4-(4-(1,2,2-triphenylvinyl)phenyl)-7-(5-(4-(1,2,2-triphenylvinyl)phenyl)thiophen-2yl)benzo[c][1,2,5]thiadiazole (BTPETTD) as a red emitter and electron-transporting layer 4,4′-bis(1-phenyl-1H-phenanthro[9,10-d]imidazol-2-yl)biphenyl (DDPi) as a blue emitter are demonstrated. The blue emission is due to direct recombination of excitons in DPPi, while the red emission originates not only from the direct recombination of excitons in BTPETTD but also from a colour down-conversion process by absorbing blue emission and re-emitting red photons. The combination of blue emission and red emission yields an efficient and extremely stable white colour, regardless of driving voltages. In our demonstration, a bi-layer WOLED with an efficiency of 4.2 cd A −1 at 1000 cd m −2 , 1931 Commision International de L'Eclairage coordinates of (0.31, 0.31) and a high colour rendering index of 92 over a wide range of driving voltages is obtained.
Read moreWith the explosive growth in data traffic, operators are faced with the challenges of transforming their existing networks through careful investment in the right technology to lower the cost per bit. In this paper, we explored the economic impact of NG-OTN technologies on future converged IP Optical transport network through a comprehensive case study of a typical service provider in Asia Pacific. The key learning from the case study could help service providers to develop cost-effective evolution strategies while fulfilling the scalability, availability and flexibility requirements.
Read moreStacking monolayers of transition metal dichalcogenides (TMDs) has led to the discovery of a plethora of new exotic phenomena, resulting from moiré pattern formation. Due to the atomic thickness and high surface-to-volume ratio of heterostructures, the interfaces play a crucial role. Fluctuations in the interlayer distance affect interlayer coupling and moiré effects. Therefore, to access the intrinsic properties of the TMD stack, it is essential to obtain a clean and uniform interface between the layers. Here, we show that this is achieved by ironing with the tip of an atomic force microscope. This post-stacking procedure dramatically improves the homogeneity of the interfaces, which is reflected in the optical response of the interlayer exciton. We demonstrate that ironing improves the layer coupling, enhancing moiré effects and reducing disorder. This is crucial for the investigation of TMD heterostructure physics, which currently suffers from low reproducibility.
Read moreElectron-electron interactions in high-mobility conductors can give rise to transport signatures resembling those described by classical hydrodynamics. Using a nanoscale scanning magnetometer, we imaged a distinctive hydrodynamic transport pattern-stationary current vortices-in a monolayer graphene device at room temperature. By measuring devices with increasing characteristic size, we observed the disappearance of the current vortex and thus verified a prediction of the hydrodynamic model. We further observed that vortex flow is present for both hole- and electron-dominated transport regimes but disappears in the ambipolar regime. We attribute this effect to a reduction of the vorticity diffusion length near charge neutrality. Our work showcases the power of local imaging techniques for unveiling exotic mesoscopic transport phenomena.
Read moreVan der Waals interactions with transition metal dichalcogenides were shown to induce strong spin-orbit coupling (SOC) in graphene, offering great promises to combine large experimental flexibility of graphene with unique tuning capabilities of the SOC. Here, we probe SOC-driven band splitting and electron dynamics in graphene on WSe<sub>2</sub> by measuring ballistic transverse magnetic focusing. We found a clear splitting in the first focusing peak whose evolution in charge density and magnetic field is well reproduced by calculations using the SOC strength of ~ 13 meV, and no splitting in the second peak that indicates stronger Rashba SOC. Possible suppression of electron-electron scatterings was found in temperature dependence measurement. Further, we found that Shubnikov-de Haas oscillations exhibit a weaker band splitting, suggesting that it probes different electron dynamics, calling for a new theory. Our study demonstrates an interesting possibility to exploit ballistic electron motion pronounced in graphene for emerging spin-orbitronics.
Read moreA new platform for position and polarization aligned 2D single-photon emitter integration within background-free silicon-nitride microring resonator is presented. Emitters achieve a cavity-enhanced coupling efficiency of 46±4%, exceeding previous demonstration by over an order-of- magnitude.
Read moreTetraphenylethene derivatives [Ph(PhCH=CHPhR)C=C(PhCH=CHPhR)Ph, R=H, CN, NO2, NPh2] with green, yellow-green, and orange emission colours were designed and synthesized. These molecules are practically non-emissive in their dilute solutions but emit intensely as nanoaggregates in poor solvents, demonstrating a novel phenomenon of aggregation-induced emission. Their blended films with poly(methyl methacrylate) also display bright emissions. Restriction of intramolecular motion in the condensed phase may be responsible for such unusual behaviour. Multilayer electroluminescence devices with a configuration of indium tin oxide/N,N'-di(1-naphthyl)-N,N'-diphenylbenzidine/emitter/tris(8-hydroxyquinolinolato)aluminum (Alq3)/LiF/Al were constructed, which gave green light with a maximum luminance and current efficiency of 12930 cd cm–2 and 3.04 cd A–1 respectively. The tetraphenylethenes can serve as excellent cell staining agents for selectively illuminating the cytoplasm and vesicles of living cells.
Read moreAn unexpected recognition of β-cyclodextrin (CD) from α- and γ-CDs was achieved. The emission from a diboronic acid-containing tetraphenylethene (TPEDB) was amplified upon addition of β-CD, whereas there was almost no response for α-, and γ-CDs. TPEDB is proposed to be anchored onto the wide rim of β-CD through the alternative and conceptually new cooperative boronic acid/diol dynamic binding interaction, resulting in the restriction of intramolecular rotations of its phenyl rings (see scheme). Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.
Read moreAbstract We revisit and extend the standard bosonic interpretation of interlayer excitons (ILX) in the moiré potential of twisted heterostructures of transition-metal dichalcogenides. In our experiments, we probe a high quality MoSe 2 /WSe 2 van der Waals bilayer heterostructure via density-dependent photoluminescence spectroscopy and reveal strongly developed, unconventional spectral shifts of the emergent moiré exciton resonances. The observation of saturating blueshifts of successive exciton resonances allow us to explain their physics in terms of a model utilizing fermionic saturable absorbers. This approach is strongly inspired by established quantum-dot models, which underlines the close analogy of ILX trapped in pockets of the moiré potential, and quantum emitters with discrete eigenstates.
Read more
