High Pressure Polymerization of 2,6-Diethynylpyridine

Pressure induced polymerization (PIP) of unsaturated molecules like aromatics is highly focused on its production of novel carbon materials like diamond nanothread and graphane. However, the high stability of the aromatic molecules results in a high polymerization pressure at room temperature. To reduce the reaction pressure of the aromatic ring, here we introduced conjugated alkynyl, investigated the PIP of 2,6-diethynylpyridine (2,6-DEP) up to 30.7 GPa, and successfully obtained one-dimensional (1-D) ordered polymers below 10 GPa. In situ Raman and IR spectra show that the alkynyl starts to react at 4–5 GPa. At 5.4 GPa, the critical crystal structure of 2,6-DEP was investigated by in situ X-ray diffraction, and the shortest intermolecular distance was determined as 2.90 Å, between the pyridine ring. The product recovered from 10 GPa shows clearly a 1-D structure via transmission electron microscopy (TEM), and strong diffractions at d = 7.5 and 5.2 Å, corresponding to the interplane distance of the stacked 1-D polymer. Theoretical simulations show that the reaction starts between the alkynyl groups, after which the aromatic rings are drawn close to each other and react. Combining the predicted reaction and the experimental result, we concluded possible models of the product. Our study shows that alkynyl is a good initiator for reducing the polymerization pressure of the aromatics and therefore allows the synthesis of ordered 1-D carbon materials in large scale

Thin-Film Lithium Niobate based Dual-Polarization IQ modulator for Single-Carrier 1.6 Tb/s Transmission

We successfully demonstrate a monolithic integrated dual-polarization (DP) IQ modulator based on thin-film lithium niobate (TFLN) platform with a silicon substrate, which consists of IQ modulators, spot-size converters (SSCs) and a polarization rotator combiner (PRC). After coupled with polarization maintaining fibers, the measured insertion loss of the modulator is 12 dB. In addition, we experimentally achieve a single-carrier 1.6 Tb/s net bitrate transmission

Tuning of Interlayer Interaction in MoS₂–WS₂ van der Waals Heterostructures Using Hydrostatic Pressure

Van der Waals heterostructures have recently attracted great interest of the scientific community due to their rich exotic physical properties and extensive application prospects. Therefore, we conducted pressure-dependent Raman and photoluminescence spectroscopic studies on MoS2–WS2 heterostructures in different twist angles (24.5 and 54°). Thus, it was confirmed that as the interlayer interaction increases under pressure, an electronic phase transition and a structural phase transition due to layer sliding are observed at ∼1.8 and ∼3.8 GPa in the HS-24.5° structures, while no phase transition is observed in the HS-54° structures. As a result of a larger tunable interlayer space in HS-24.5° structures, optical properties of HS-24.5° structures are more pressure-sensitive than those of the HS-54° structure. It is expected that this work will help comprehensively establish the correlation between the interlayer interactions and optical properties of vdW HSs at the atomic level. Understanding this correlation is crucial for the development of new excitonic devices

Pressure-Induced Hydrogen Transfer in 2‑Butyne via a Double CH···π Aromatic Transition State

Hydrogen transfer (H-transfer) is an important elementary reaction in chemistry and bioscience. It is often facilitated by the hydrogen bonds between the H-donor and acceptor. Here, at room temperature and high pressure, we found that solid 2-butyne experienced a concerted two-in–two-out intermolecular CH···π H-transfer, which initiated the subsequent polymerization. Such double H-transfer goes through an aromatic Hückel six-membered ring intermediate state via intermolecular CH···π interactions enhanced by external pressure. Our work shows that H-transfer can occur via the CH···π route in appropriate conformations under high pressure, which gives important insights into the H-transfer in solid-state hydrocarbons

High-Pressure Synthesis of Highly Conjugated Polymers via Synergistic Polymerization of Phenylpropiolic Acid

The synergistic reaction between alkyne and phenyl groups is a promising pathway for decreasing the reaction pressures of aromatics and enabling scalable high-pressure synthesis of carbon materials via pressure-induced polymerization (PIP). Here by combining theoretical calculations and experimental data, we demonstrate that a simultaneous polymerization of alkynyl and phenyl groups occurred in phenylpropiolic acid (PPA) with the threshold distance dC···C = 3.3 Å, generating an extended structure consisting of sp2 and sp3 carbons. The reaction pressure of phenyl was significantly decreased to ∼5 GPa, which can be applied for large-scale synthesis. The product has a large π-electron conjugated system, resulting in a band gap energy reduced to 1.65 eV and an electrical conductivity increasing to 1.24 × 10–6 S · cm–1. Our research confirmed that conjugated polymers can be synthesized at lower pressures via the high-pressure synergistic reaction route of phenylethynyl compounds and can be used to further realize applications in organic photovoltaic devices

High Performance Thin-film Lithium Niobate Modulator Applied ITO Composite Electrode with Modulation Efficiency of 1V*cm

Thin film lithium niobate (TFLN) based electro-optic modulator is widely applied in the field of broadband optical communications due to its advantages such as large bandwidth, high extinction ratio, and low optical loss, bringing new possibilities for the next generation of high-performance electro-optic modulators. However, the modulation efficiency of TFLN modulators is still relatively low when compared with Silicon and Indium-Phosphide (InP) based competitors. Due to the restriction of the trade-off between half-wave voltage and modulation length, it is difficult to simultaneously obtain low driving voltage and large modulating bandwidth. Here, we break this limitation by introducing Transparent Conductive Oxide (TCO) film, resulting in an ultra-high modulation efficiency of 1.02 V*cm in O-Band. The fabricated composite electrode not only achieves high modulation efficiency but also maintains a high electro-optic bandwidth, as demonstrated by the 3 dB roll-off at 108 GHz and the transmission of PAM-4 signals at 224 Gbit/s. Our device presents new solutions for the next generation of low-cost high-performance electro-optic modulators. Additionally, it paves the way for downsizing TFLN-based multi-channel optical transmitter chips

From Biomass to Functional Crystalline Diamond Nanothread: Pressure-Induced Polymerization of 2,5-Furandicarboxylic Acid

2,5-Furandicarboxylic acid (FDCA) is one of the top-12 value-added chemicals from sugar. Besides the wide application in chemical industry, here we found that solid FDCA polymerized to form an atomic-scale ordered sp3-carbon nanothread (CNTh) upon compression. With the help of perfectly aligned π–π stacked molecules and strong intermolecular hydrogen bonds, crystalline poly-FDCA CNTh with uniform syn-configuration was obtained above 11 GPa, with the crystal structure determined by Rietveld refinement of the X-ray diffraction (XRD). The in situ XRD and theoretical simulation results show that the FDCA experienced continuous [4 + 2] Diels–Alder reactions along the stacking direction at the threshold C···C distance of ∼2.8 Å. Benefiting from the abundant carbonyl groups, the poly-FDCA shows a high specific capacity of 375 mAh g–1 as an anode material of a lithium battery with excellent Coulombic efficiency and rate performance. This is the first time a three-dimensional crystalline CNTh is obtained, and we demonstrated it is the hydrogen bonds that lead to the formation of the crystalline material with a unique configuration. It also provides a new method to move biomass compounds toward advanced functional carbon materials

Crystalline Fully Carboxylated Polyacetylene Obtained under High Pressure as a Li-Ion Battery Anode Material

Substituted polyacetylene is expected to improve the chemical stability, physical properties, and combine new functions to the polyacetylene backbones, but its diversity is very limited. Here, by applying external pressure on solid acetylenedicarboxylic acid, we report the first crystalline poly-dicarboxylacetylene with every carbon on the trans-polyacetylene backbone bonded to a carboxyl group, which is very hard to synthesize by traditional methods. The polymerization is evidenced to be a topochemical reaction with the help of hydrogen bonds. This unique structure combines the extremely high content of carbonyl groups and high conductivity of a polyacetylene backbone, which exhibits a high specific capacity and excellent cycling/rate performance as a Li-ion battery (LIB) anode. We present a completely functionalized crystalline polyacetylene and provide a high-pressure solution for the synthesis of polymeric LIB materials and other polymeric materials with a high content of active groups

Arylazo under Extreme Conditions: [2 + 2] Cycloaddition and Azo Metathesis

The four-membered nitrogen ring (N4-ring) is predicted to be a high-energy density moiety and has been the target of chemical synthesis for quite a long time. Here, by compressing the 1:1 co-crystal of trans-azobenzene and trans-perfluoroazobenzene up to ∼40 GPa, the azo groups were restrained closely in parallel in the crystal and underwent two competitive addition reactions. One is [4 + 2] cycloaddition with the azo group as a part of diene and phenyl as dienophile. The other is [2 + 2] cycloaddition between two azo groups, which produced an unprecedented N4-ring structure as evidenced by the metathesis product. The content of the N4-ring structure significantly increases under higher pressure, and we found that it was the external pressure that decreased the kinetic barrier and realized such a high-tensile moiety. Our work shows that high pressure is an alternative synthetic strategy for these high-tensile structures, which can be very effective under the cooperation of crystal engineering