Ether Units Research Articles

One‐Step Synthesis of Multi‐Block Copolymers of Isotactic Polypropylene (iPP) and Theoretical Studies on the Regioselectivity and Stereoselectivity of Polypropylene

ABSTRACTFor multi‐block copolymers, using a one‐step synthesis route can avoid repeating addition of monomers during the reaction, thereby preventing the contamination of polymerization reaction and the accidental termination of the polymer chain. For this purpose, described herein is a simple and efficient approach for synthesizing topological structure multi‐block copolymers of isotactic polypropylene by copolymerizing ethylene, propylene and higher α‐olefins by [N, Si, N, P] multi‐chelated complexes ({P(C6H5)2‐N(C6H5)‐(CH3)2Si‐N‐2,4,6‐(F)3C6H2}ZrCl3). In this contribution, the complexes are found to exhibit high polymerization activity (up to 9.5 × 106gP (mol ∙ Zr)−1 ∙ h−1) and relatively high incorporation content of 1‐octene (up to 15 mol%). Density functional theory (DFT) was used to study the mechanism of copolymerization reaction. The results showed that propylene monomer is more prone to 1,2‐insertion in kinetics to obtain iPP. Different lengths of iPP segments in the copolymer (terpolymer) chain not only led to different melting points but also block the terpolymer of propylene, ethylene and higher α‐olefins. Enhancing α‐olefins and ethylene units within the copolymer chain will also destroy the layered polypropylene crystals. Furthermore, the crystallizable polyethylene segment was not observed, implying that ethylene only participates in forming the random segments in the copolymer chains. Most importantly, polypropylene thermoplastic elastomer with good elasticity can be produced by the copolymerization of propylene with ethylene and 1‐octene.

Supramolecular chemistry in solution and solid-gas interfaces: synthesis and photophysical properties of monocolor and bicolor fluorescent sensors for barium tagging in neutrinoless double beta decay.

Translation of photophysical properties of fluorescent sensors from solution to solid-gas environments via functionalized surfaces constitutes a challenge in chemistry. In this work, we report on the chemical synthesis, barium capture ability and photophysical properties of two families of monocolor and bicolor fluorescent sensors. These sensors were prepared to capture barium cations that can be produced in neutrinoless double beta decay of Xe-136. These sensors incorporate crown ether units, two different fluorophores, aliphatic spacers of different lengths, and a silatrane linker that forms covalent bonds with indium tin oxide (ITO) surfaces. Both species shared excellent Ba2+ binding abilities. Fluorescent monocolor indicators (FMIs), based on naphthyl fluorophores, showed an off-on character in solution controlled by photoinduced electron transfer. Fluorescent bicolor indicators (FBIs), based on benzo[a]imidazo[5,1,2-cd] fluorophores, exhibited a significant change in their emission spectra on going from the free to the barium-bound state. Both FMIs and FBIs showed similar photophysics in solution and on ITO. However, their performance on ITO was found to be attenuated, but not fully extinguished, with respect to the values obtained in solution, both in terms of intensity and selectivity between the free and Ba2+-bound states. Despite this issue, improved performance of the FBIs based on confocal microscopy of the directly attached molecules was observed. These selective FMI and FBI chemosensors installed on tailor-made functionalized surfaces are promising tools to capture the barium cations produced in the double beta decay of Xe-136. The identification of this capture would boost the sensitivity of the experiments searching for the Xe-136-based neutrinoless double beta decay, as backgrounds would be almost totally suppressed.

TVT-Based New Building Block with Enhanced π-Electron Delocalization for Efficient Non-Fused Photovoltaic Acceptor.

To address the high-cost issue that impedes the large-scale fabrication and industrialization of organic solar cells (OSCs), it is crucial to design low-cost photovoltaic materials with simplified synthesis procedures. In this study, a novel fully non-fused acceptor, ATVT-BO, featuring a triisopropylbenzene-substituted (E)-1,2-di(thiophen-2-yl)ethene (TVT) unit as the central core is designed and synthesized. A control acceptor, A4T-BO, with the same alkyl chains but a bithiophene central core, is also synthesized for comparison. Theoretical calculations and practical measurements reveal that compared to A4T-BO, the insertion of an ethylene bond in ATVT-BO enhances the molecular planarity and reduces the aromaticity, leading to enhanced π-electron delocalization and thus improved electron mobility and a red-shifted optical absorption spectrum. The 3D molecular packing mode of ATVT-BO, characterized by tight intermolecular interactions, also promotes efficient charge transport in OSCs. Consequently, when paired with the low-cost polymer PTVT-T, featuring an ester-substituted TVT structure, as the photoactive layer, the PTVT-T:ATVT-BO-based device achieves a remarkable power conversion efficiency of 14.8%, distinctly higher than that of PTVT-T:A4T-BO-based cell. The result highlights the significant potential of TVT units in creating both low-cost polymer donors and fully non-fused acceptors, which opens up new possibilities for designing low-cost photoactive materials in OSCs.

Synthesis of poly(terphenyl-co-dibenzo-18-crown-6 methylimidazole) copolymers for high-performance high temperature polymer electrolyte membrane fuel cells

This study focuses on the development of high temperature polymer electrolyte membranes (HT-PEMs), which are essential components for HT-PEM fuel cells (HT-PEMFCs). While phosphoric acid (PA) doped polybenzimidazole (PBI) has been recognized as a successful HT-PEM, it faces several challenges, including the use of carcinogenic monomer, complex synthesis processes, and poor solubility in organic solvents. To produce more cost-effective, easily synthesized, and high-performance alternatives, this study utilizes a straightforward superacid-catalyzed Friedel-Crafts reaction to synthesize a series of poly(terphenyl-co-dibenzo-18-crown-6 methylimidazole) copolymers, referred to as Co-x%TP-y%CE-Im, using p-terphenyl, dibenzo-18-crown-6 and 1-methyl-1H-imidazole-2-formaldehyde as monomers. The copolymerized hydrophilic and bulky crown ether units introduce substantial free volume and multiple interaction sites with PA molecules, as indicated by theoretical calculations. Additionally, the formation of microphase separation structures, confirmed by atomic force microscope (AFM) and transmission electron microscope (TEM), contributes to the enhanced performance of these membranes. For instance, after immersion in 85 wt% and 75 wt% PA solutions, the Co-90%TP-10%CE membrane achieves PA doping contents of 200 % and 169 %, achieving high conductivities of 0.092 S cm−1 and 0.054 S cm−1 at 180 °C, while maintaining tensile strengths of 6.5 MPa and 7.5 MPa at room temperature. Without the need for humidification or backpressure, the peak power density of an H2-O2 cell equipped with Co-90%TP-10%CE/169%PA membrane with a thickness of 79 μm reaches an impressive 1018 mW cm−2 at 210 °C. These results demonstrate new materials and insights for the development of high-performance HT-PEMs.

Helical Star-Shaped Bottlebrush Polymers: From Controlled Synthesis to Tunable Photoluminescence and Circularly Polarized Luminescence.

The controlled synthesis of star-shaped bottlebrush polymers with tunable topologies is a challenge. However, such materials may exhibit distinct photoluminescence properties. Bottlebrush polymers have polymerization-induced emission (PIE) properties due to their aggregated side chains, and aggregation-induced emission (AIE) is also a unique luminescent property. In this work, we prepared a variety of highly active alkyne Pd catalysts and polymerized poly(L/D-lactic acid) macromonomers containing polymerizable phenylisocyanide groups as end groups to obtain a variety of topologically structured bottlebrush polymers with controllable molecular weights and narrow molecular weight distributions. Bottlebrush polymers with tetraphenyl ethylene (TPE) units as the core exhibit tunable photoluminescence and circularly polarized luminescence properties. We propose that such properties are due to the unique AIE characteristics of the TPE unit combined with the PIE characteristics of the bottlebrush polymer.

Vinyl Ether Maleic Acid Polymers: Tunable Polymers for Self-Assembled Lipid Nanodiscs and Environments for Membrane Proteins.

Native lipid bilayer mimetics, including those that use amphiphilic polymers, are important for the effective study of membrane-bound peptides and proteins. Copolymers of vinyl ether monomers and maleic anhydride were developed with controlled molecular weights and hydrophobicity through reversible addition-fragmentation chain-transfer polymerization. After polymerization, the maleic anhydride units can be hydrolyzed, giving dicarboxylates. The vinyl ether and maleic anhydride copolymerized in a close to alternating manner, giving essentially alternating hydrophilic maleic acid units and hydrophobic vinyl ether units along the backbone after hydrolysis. The vinyl ether monomers and maleic acid polymers self-assembled with lipids, giving vinyl ether maleic acid lipid particles (VEMALPs) with tunable sizes controlled by either the vinyl ether hydrophobicity or the polymer molecular weight. These VEMALPs were able to support membrane-bound proteins and peptides, creating a new class of lipid bilayer mimetics.

Promoting the spatial arrangement of TTF to optimize the photocurrent response of MOFs

The arrangement of Tetrathiafulvalene (TTF) plays a critical role in modulating the photocurrent responses of MOFs. In this work, employing m-H4-TTFTB as the building block and Cd as the metal center, two distinct MOF materials were selectively synthesized, and one MOF is different from the another one due to the incorporating of the (E)-1,2-di (pyridin-4-yl)ethene (BPE) unit. The MOF comprised solely of 3,3′,3″,3‴-([2,2′-bi (1,3-dithiolylidene)]-4,4′,5,5′-tetrayl)tetrabenzoic acid (m-H4-TTFTB) ligands showcased a 2D spatial arrangement. Differently, the introduction of the BPE unit facilitated the transition from a 2D to a 3D MOF architecture. The resulting 3D MOF exhibited an enhanced thermal stability compared to its 2D counterpart. Nevertheless, owing to the denser TTF arrangement demonstrated by the 2D MOF, its photoresponse performance also proved superior, approximately 1.2 times that of the Cd-BPE-m-TTFTB crystal.

Phenolic syringyl end groups in 13C-enriched hardwoods detected and quantified by solid-state NMR

While syringyl units are the most abundant monolignols in hardwood lignin, their phenolic (i.e. hydroxyl) end group concentration has not been measured. In two uniformly 13C-enriched young hardwoods, from beech and oak, the syringyl units were quantitatively investigated by advanced solid-state 13C NMR. Small signals of OH-terminated syringyl units were resolved in spectrally edited two-dimensional 13C–13C NMR spectra of the two hardwoods. Their distinct peak positions predicted based on literature data were validated via the abundant OH-terminated syringyl units in hydrolyzed 13C-beechwood. In a two-dimensional 13C–13C exchange spectrum with diagonal-ridge suppression, a well-resolved peak of phenolic syringyl units was observed at the characteristic C–H peak position of syringyl rings, without significant overlap from guaiacyl peaks. Accurate 13C chemical shifts of regular and end-group syringyl units were obtained. Through spectrally edited 2D NMR after 1H inversion recovery, phenols of condensed tannin complexed with arginine were carefully analyzed and shown to overlap minimally with signals from phenolic syringyl units. The local structure and resulting spin dynamics of ether (chain) and hydroxyl (end-group) syringyl units are nearly the same, enabling quantification by peak integration or deconvolution, which shows that phenolic syringyl end groups account for 2 ± 1 % of syringyl units in beechwood and 5 ± 2 % in oakwood. The observed low end-group concentration needs to be taken into account in realistic molecular models of hardwood lignin structure.

The mechanism insight into the cooperative coordination of Aza-18-crown-6 ether with diglycolamide by p-benzyl as linkers enhancing the selectivity for heavy REEs(III)

The development of new ligands is crucial for the functional application of REEs(III), because the coordination compounds of rare-earth elements (REEs) have many important applications in pharmaceuticals and nuclear medicine. In this paper, a novel ligand (Cr6-Bz-DGA) with the aza-crown ether and diglycolamide (DGA) units was designed to coordinate with light, medium, and heavy REEs(III). It was found that M/L = 2:2 species (aza-crown ether-REEs(III)-DGA connection) was the thermodynamically stable complex. The stability constants of Nd(III), Eu(III), and Ho(III) complexes were determined by UV–Vis and fluorescence titration, respectively, which were logβNd = 7.49 ± 0.019, logβEu = 7.10 ± 0.013 and logβHo = 8.27 ± 0.032. The variation of fluorescence lifetime suggested that the Eu(III) ion was exclusively coordinated by the ligand with coordination number 9 in the inner sphere of the Eu(III) ion. The shifts of 1H NMR revealed that there are different coordination between the ligand and REEs(III). For larger ionic radii La(III), three O atoms of the DGA unit and five O and one N atoms of the aza-crown ether unit were supplied. While, for Y(III)/Lu(III) with smaller ion radii, the ligand supplied three O atoms from the DGA and one N atom and only two O atoms from the aza-crown ether. The displacement experiment of REEs(III) combined with ligand and the fitted stability constants prove that the smaller ionic radii REEs(III) more strongly bind with ligand than larger ionic radius REEs(III). These results may help understand the coordination behavior of REEs(III) and expand their potential applications.

Feasibility of Repairing Concrete with Ultra-High Molecular Weight Polyethylene Fiber Cloth: A Comprehensive Literature Review

This review explores the use of Ultra-High Molecular Weight Polyethylene (UHMWPE) fiber cloth as an innovative solution for the repair and reinforcement of concrete structures. UHMWPE is a polymer formed from a very large number of repeated ethylene (C2H4) units with higher molecular weight and long-chain crystallization than normal high-density polyethylene. With its superior tensile strength, elongation, and energy absorption capabilities, UHMWPE emerges as a promising alternative to traditional reinforcement materials like glass and carbon fibers. The paper reviews existing literature on fiber-reinforced polymer (FRP) applications in concrete repair in general, highlighting the unique benefits and potential of UHMWPE fiber cloth compared to other commonly used methods of strengthening concrete structures, such as enlarging concrete sections, near-surface embedded reinforcement, and externally bonded steel plate or other FRPs. Despite the scarcity of experimental data on UHMWPE for concrete repair, this review underscores its feasibility and calls for further research to fully harness its capabilities in civil engineering applications.

Phase Morphology Dependence of Ionic Conductivity and Oxidative Stability in Fluorinated Ether Solid-State Electrolytes.

Solid-state polymer electrolytes can enable the safe operation of high energy density lithium metal batteries; unfortunately, they have low ionic conductivity and poor redox stability at electrode interfaces. Fluorinated ether polymer electrolytes are a promising approach because the ether units can solvate and conduct ions, while the fluorinated moieties can increase oxidative stability. However, current perfluoropolyether (PFPE) electrolytes exhibit deficient lithium-ion coordination and ion transport. Here, we incorporate cross-linked poly(ethylene glycol) (PEG) units within the PFPE matrix and increase the polymer blend electrolyte conductivity by 6 orders of magnitude as compared to pure PFPE at 60 °C from 1.55 × 10-11 to 2.26 × 10-5 S/cm. Blending varying ratios of PEG and PFPE induces microscale phase separation, and we show the impact of morphology on ion solvation and dynamics in the electrolyte. Spectroscopy and simulations show weak ion-PFPE interactions, which promote salt phase segregation into-and ion transport within-the PEG domain. These polymer electrolytes show promise for use in high-voltage lithium metal batteries with improved Li|Li cycling due to enhanced mechanical properties and high-voltage stability beyond 6 V versus Li/Li+. Our work provides insights into transport and stability in fluorinated polymer electrolytes for next-generation batteries.

Light-Induced Reactivity Switch at O2-Activating Bioinspired Copper(I) Complexes.

Using light to unveil unexplored reactivities of earth-abundant metal-oxygen intermediates is a formidable challenge, given the already remarkable oxidation ability of these species in the ground state. However, the light-induced reactivity of Cu-O2 intermediates still remains unexplored, due to the photoejection of O2 under irradiation. Herein, we describe a photoinduced reactivity switch of bioinspired O2-activating CuI complexes, based on the archetypal tris(2-pyridyl-methyl)amine (TPA) ligand. This report represents a key precedent for light-induced reactivity switch in Cu-O2 chemistry, obtained by positioning C-H substrates in close proximity of the active site. Open and caged CuI complexes displaying an internal aryl ether substrate were evaluated. Under light, a Cu-O2 mediated reaction takes place that induces a selective conversion of the internal aryl ether unit to a phenolate-CH2- moiety with excellent yields. This light-induced transformation displays high selectivity and allows easy postfunctionalization of TPA-based ligands for straightforward preparation of challenging heteroleptic structures. In the absence of light, O2 activation results in the standard oxidative cleavage of the covalently attached substrate. A reaction mechanism that supports a monomeric cupric-superoxide-dependent reactivity promoted by light is proposed on the basis of reactivity studies combined with (TD-) DFT calculations.

Thermal Oxidative Aging and Service Life Prediction of Commercial Ethylene-Propylene-Diene Monomer Spacer Damping Composites for High-Voltage Transmission Lines.

The aging behavior and life prediction of rubber composites are crucial for ensuring high-voltage transmission line safety. In this study, commercially available ethylene-propylene-diene monomer (EPDM) spacer composites were chosen and investigated to elucidate the structure and performance changes under various aging conditions. The results showed an increased C=O peak intensity with increasing aging time, suggesting intensified oxidation of ethylene and propylene units. Furthermore, the surface morphology of commercial EPDM composites displayed increased roughness and aggregation after aging. Furthermore, hardness, modulus at 100% elongation, and tensile strength of commercial EPDM composites exhibited a general increase, while elongation at break decreased. Additionally, the damping performance decreased significantly after aging, with a 20.6% reduction in loss factor (20 °C) after aging at 100 °C for 672 h. With increasing aging time and temperature, the compression set gradually rose due to the irreversible movement of the rubber chains under stress. A life prediction model was developed based on a compression set to estimate the lifetime of rubber composites for spacer bars. The results showed that the product's life was 8.4 years at 20 °C. Therefore, the establishment of a life prediction model for rubber composites can provide valuable technical support for spacer product services.

Highly efficient non-doped organic light emitting diodes based on phenanthreneimidazole derivatives with hot exciton mechanism

Organic light-emitting diodes (OLEDs) promise many advantages for next-generation illumination and future display applications. Developing organic metal-free fluorescent emitter with wide bandgap and high efficiency is both significant and challenging in OLEDs. Here, phenanthroimidazole (PI) unit possessing ultraviolet emission is connected with biphenyl, diphenylmethane and diphenyl ether moieties to construct a series of blue luminogens of PPIDPh, PPIDPhC and PPIDPhO with hot exciton character. PPIDPh with biphenyl substituent at C2 position of PI group exhibits emission peak at 454 nm in non-doped film. The integration of diphenylmethane and diphenyl ether units with PI group in PPIDPhC and PPIDPhO further limits the π-conjugation owing to sp3 hybridized carbon atom and oxygen atom, which results in bluer emission peaking at 433 nm and 437 nm in the aggregated state, respectively. Particularly, the maximum external quantum efficiency (EQEmax) of PPIDPh-based non-doped OLED reaches 10.33 % with CIE coordinates of (0.15, 0.10) and subtle efficiency roll-off of only 7.4 % at high brightness of 1000 cd m−2. The PPIDPhC and PPIDPhO-based non-doped devices display even better color purity with high EQEmax of 8.56 % and 7.90 %, Commission Internationale de ĺEclairage (CIE) coordinates of (0.17, 0.08) and (0.16, 0.08), respectively, matching well with National Television Standards Committee (NTSC) requirement for saturated blue color. Such result is among the best outcomes of non-doped blue fluorescent OLEDs with the same emission color. This result will also shed light on the further development of efficient organic wide bandgap emitter and corresponding high-performance OLED.

Design of sec-Benzyl Vinyl Ethers toward the Synthesis of Alternating Copolymers Composed of Vinyl Alcohol and Vinyl Ether Units.

In this work, we designed benzyl vinyl ethers carrying alkyl substituents at the benzyl position (i.e., sec-BnVEs) as bulky, reactive, and transformable monomers to realize the alternating cationic copolymerization with an alkyl vinyl ether (VE). In particular, the isopropyl substitution caused not only the bulkiness to suppress the successive propagation but also an enhancement of the vinyl group reactivity to promote crossover propagation with a less bulky VE comonomer. The isopropyl-substituted BnVE (iPr-BnVE) underwent living cationic alternating copolymerization with n-butyl VE (nBVE), and the alternating propagation was strongly suggested by the reactivity ratios. The subsequent deprotection of the sec-benzyl pendant afforded the vinyl alcohol (VA)-nBVE alternating copolymer, and the corresponding statistical copolymer was also synthesized by using the nonsubstituted monomer (BnVE) instead of iPr-BnVE. The alternating copolymer exhibited a higher glass transition temperature, which likely stems from the uniform and efficient hydrogen-bonding formation due to the periodic sequence.

Synthesis and Properties of Vinyl Ether and Acrylonitrile Copolymers

AbstractThe radical copolymerizations of vinyl ethers, including ethylene glycol monovinyl ether (HEVE) and isobutyl vinyl ether (IBVE), and acrylonitrile (AN) are investigated. The reactivity ratios of comonomers are evaluated by Fineman–Ross (rHEVE = 0.032 and rAN = 1.054, and rIBVE = 0.031 and rAN = 13.984) and Kelen–Tudos (rHEVE = 0.001 and rAN = 1.036, and rIBVE = 0.032 and rAN = 13.981) methods, respectively. The conversions of HEVE and IBVE under similar conditions also support that HEVE has a higher reactivity than that of IBVE. A series of poly(HEVE‐co‐AN)s (Mn from 56 000 to 110 000) and poly(IBVE‐co‐AN)s (Mn from 52 000 to 97 000) with random sequential structure are prepared. Furthermore, the glass transitional temperatures of poly(vinyl ether‐co‐AN)s decrease with the increase of vinyl ether units in the copolymers. Thermal stability of poly(vinyl ether‐co‐AN)s is comparable, which is slightly affected by vinyl ether contents. Poly(HEVE‐co‐AN)s possess a two‐stage weight loss (one around 230 °C, and the other around 300 °C), and poly(IBVE‐co‐AN)s decompose at around 350 °C with one stage. In addition, the poly(HEVE‐co‐AN)s demonstrate a good hydrophilicity of which the average of static water contact angles decrease from 85.4° to 62.4° with the HEVE units increased from 8% to 33%.

Mechanically Interlocked Interphase with Energy Dissipation and Fast Li-Ion Transport for High-Capacity Lithium Metal Batteries.

Constructing an artificial solid electrolyte interphase (ASEI) on Li metal anodes (LMAs) is a potential strategy for addressing the dendrite issues. However, the mechanical fatigue of the ASEI caused by stress accumulation under the repeated deformation from the Li plating/stripping is not taken seriously. Herein, this work introduces a mechanically interlocked [an]daisy chain network (DC MIN) into the ASEI to stabilize the Li metal/ASEI interface by combining the functions of energy dissipation and fast Li-ion transport. The DC MIN featured by large-range molecular motions is cross-linked via efficient thiol-ene click chemistry; thus, the DC MIN has flexibility and excellent mechanical properties. As an ASEI, the crown ether units in DC MIN not only interact with the dialkylammonium of a flexible chain, forming the energy dissipation behavior but also coordinate with Li ion to support the fast Li-ion transport in DC MIN. Therefore, a stable 2800h-symmetrical cycling (1mA cm-2 ) and an excellent 5 C-rate (full cell with LiFePO4 ) performance are achieved by DC MIN-based ASEI. Furthermore, the 1-Ah pouch cell (LiNi0.88 Co0.09 Mn0.03 O2 cathode) with DC MIN-coated LMA exhibits improved capacity retention (88%) relative to the Control. The molecular design of DC MIN provides new insights into the optimization of an ASEI for high-energy LMAs.

3D Crown Ether Covalent Organic Framework as Interphase Layer toward High-Performance Lithium Metal Batteries.

The practical application of lithium (Li) metal batteries is inhibited by accumulative Li dendrites and continuous active Li consumption during cycling, which results in a low Coulombic efficiency and short lifetime. Constructing artificial solid-electrolyte interphase (SEI) layer in Li anode, such as 2D covalent organic frameworks (COFs), is an effective strategy to restrain the formation of Li dendrites and improve cycling performance. However, the exploration of 3D COFs as protecting layers is rarely reported, because of the preconception that the interconnect pores in 3D COFs eventually cause Li dendrites in disordered direction. 3D crown ether-based COF with ffc topology as interphase layer, in which the crown ether units are arranged in parallel and vertical orientation along the electrode, is demonstrated. The strong coupling effect between the crown ether and Li+ accelerates Li+ diffusion kinetics and enables homogeneous Li+ flux, resulting in a high Li+ transference number of 0.85 and smooth Li deposition in 3D direction. Li/COF-Cu cells display a lower Li-nucleation overpotential (17.4mV) and high average Coulombic efficiency of ≈98.6% during 340 cycles with COF incorporation. This work gives a new insight into designing COFs for energy storage systems.

Asymmetric catalytic [1,3]- or [3,3]-sigmatropic rearrangement of 3-allyloxy-4H-chromenones and their analogues.

A highly efficient asymmetric [1,3]- and [3,3]-O-to-C sigmatropic rearrangement of 3-allyloxy-4H-chromenones and their analogues was developed. Chiral N,N'-dioxide complexes of 3d late transition metal complexes enabled two mechanistically different processes, giving a series of optically active 2,2-disubstituted chromane-3,4-diones and 2-allyl-3-hydroxy-4H-chromen-4-ones as well as their related compounds in excellent yield and enantioselectivity. Systemic mechanistic studies and DFT calculation revealed the nature of the vinyl ether unit of the substrate, which biased regioselectivity via a stepwise tight ion pair pathway and a concerted pericyclic pathway, respectively. The enantioselectivity of the two processes is also disclosed.

Amphiphilic Polyurethane with Cluster-Induced Emission for Multichannel Bioimaging in Living Cell Systems.

The development of single-component materials with low cytotoxicity and multichannel fluorescence imaging capability is a research hotspot. In the present work, highly electron-deficient pyrazine monomers were covalently connected into a polyurethane backbone using addition polymerization with terminal poly(ethylene glycol) monomethyl ether units containing a high density of electron pairs. Thereby, an amphiphilic polyurethane-pyrazine (PUP) derivative has been synthesized. The polymer displays cluster-induced emission through compact inter- and/or intramolecular noncovalent interactions and extensive through-space electron coupling and delocalization. Molecular rigidity facilitates red-shifted emission. Based on hydrophilic/hydrophobic interactions and excitation dependence emission at low concentrations, PUP has been self-assembled into fluorescent nanoparticles (PUP NPs) without additional surfactant. PUP NPs have been used for cellular multicolor imaging to provide a variety of switchable colors on demand. This work provides a simple molecular design for environmentally sustainable, luminescent materials with excellent photophysical properties, biocompatibility, low cytotoxicity, and color modulation.