Helical polymers for dissymmetric circularly polarized light imaging.

Control of the spin angular momentum (SAM) carried in a photon provides a technologically attractive element for next-generation quantum networks and spintronics1-5. However, the weak optical activity and inhomogeneity of thin films from chiral molecular crystals result in high noise and uncertainty in SAM detection. Brittleness of thin molecular crystals represents a further problem for device integration and practical realization of chiroptical quantum devices6-10. Despite considerable successes with highly dissymmetric optical materials based on chiral nanostructures11-13, the problem of integration of nanochiral materials with optical device platforms remains acute14-16. Here we report a simple yet powerful method to fabricate chiroptical flexible layers via supramolecular helical ordering of conjugated polymer chains. Their multiscale chirality and optical activity can be varied across the broad spectral range by chiral templating with volatile enantiomers. After template removal, chromophores remain stacked in one-dimensional helical nanofibrils producing a homogeneous chiroptical layer with drastically enhanced polarization-dependent absorbance, leading to well-resolved detection and visualization of SAM. This study provides a direct path to scalable realization of on-chip detection of the spin degree of freedom of photons necessary for encoded quantum information processing and high-resolution polarization imaging.

Depolymerization of plastics by means of electrified spatiotemporal heating.

Depolymerization is a promising strategy for recycling waste plastic into constituent monomers for subsequent repolymerization1. However, many commodity plastics cannot be selectively depolymerized using conventional thermochemical approaches, as it is difficult to control the reaction progress and pathway. Although catalysts can improve the selectivity, they are susceptible to performance degradation2. Here we present a catalyst-free, far-from-equilibrium thermochemical depolymerization method that can generate monomers from commodity plastics (polypropylene (PP) and poly(ethylene terephthalate) (PET)) by means of pyrolysis. This selective depolymerization process is realized by two features: (1) a spatial temperature gradient and (2) a temporal heating profile. The spatial temperature gradient is achieved using a bilayer structure of porous carbon felt, in which the top electrically heated layer generates and conducts heat down to the underlying reactor layer and plastic. The resulting temperature gradient promotes continuous melting, wicking, vaporization and reaction of the plastic as it encounters the increasing temperature traversing the bilayer, enabling a high degree of depolymerization. Meanwhile, pulsing the electrical current through the top heater layer generates a temporal heating profile that features periodic high peak temperatures (for example, about 600 °C) to enable depolymerization, yet the transient heating duration (for example, 0.11 s) can suppress unwanted side reactions. Using this approach, we depolymerized PP and PET to their monomers with yields of about 36% and about 43%, respectively. Overall, this electrified spatiotemporal heating (STH) approach potentially offers a solution to the global plastic waste problem.

Efficient and Modular Biofunctionalization of Thiophene-Based Conjugated Polymers through Embedded Latent Disulfide.

Biofunctionalized conjugated polymers (i.e., carrying enzymes, antibodies, and nucleic acids) are of great interest for many biological applications, yet efficient biofunctionalization of conjugated polymers under biocompatible conditions is challenging. We report a facile strategy to make biofunctionalized conjugated polymers through thiol-ene chemistry with embedded latent disulfide functional groups. This is made possible through the design of a cyclic disulfide-containing dioxythiophene, which can be integrated into a series of conjugated polymers via acid-catalyzed chain-growth polymerization. The utility of such a biofunctionalized polymer with glucose oxidase has been examined in organic electrochemical transistors for the selective sensing of glucose. This work provides a venue for the creation of biofunctional organic semiconductors.

Reductive Doping Inhibits the Formation of Isomerization-Derived Structural Defects in N-doped Poly(benzodifurandione) (n-PBDF).

Recently, solution-processable n-doped poly(benzodifurandione) (n-PBDF) has been made through in-situ oxidative polymerization and reductive doping, which exhibited exceptionally high electrical conductivities and optical transparency. The discovery of n-PBDF is considered a breakthrough in the field of organic semiconductors. In the initial report, the possibility of structural defect formation in n-PBDF was proposed, based on the observation of structural isomerization from (E)-2H,2'H-[3,3'-bibenzofuranylidene]-2,2'-dione (isoxindigo) to chromeno[4,3-c]chromene-5,11-dione (dibenzonaphthyrone) in the dimer model reactions. In this study, we present clear evidence that structural isomerization is inhibited during polymerization. We reveal that the dimer (BFD1) and the trimer (BFD2) can be reductively doped by several mechanisms, including hydride transfer, forming charge transfer complexes (CTC) or undergoing an integer charge transfer (ICT) with reactants available during polymerization. Once the hydride transfer adducts, the CTC, or the ICT product forms, structural isomerization can be effectively prevented even at elevated temperatures. Our findings provide a mechanistic understanding of why isomerization-derived structural defects are absent in n-PBDF backbone. It lays a solid foundation for the future development of n-PBDF as a benchmark polymer for organic electronics and beyond.

Highly Conductive and Solution-Processable n-Doped Transparent Organic Conductor.

Transparent conductors (TCs) play a vital role in displays, solar cells, and emerging printed electronics. Here, we report a solution-processable n-doped organic conductor from copper-catalyzed cascade reactions in the air, which involves oxidative polymerization and reductive doping in one pot. The formed polymer ink is shelf-stable over 20 days and can endure storage temperatures from -20 to 65 °C. The optimized n-doped thin-film TC exhibits a low sheet resistance of 45 Ω/sq and a high transmittance (T550 > 80%), which can rival indium tin oxide. The transparent organic conductor exhibits excellent durability under accelerated weathering tests (85 °C/85% RH). Furthermore, the n-doped polymer film can also function as an electrode material with a high volumetric capacity. When it is paired with p-doped PEDOT:PSS, a record-high coloration efficiency is obtained in a dual-polymer electrochromic device.

Circularly Recyclable Polymers Featuring Topochemically Weakened Carbon-Carbon Bonds.

Closed-loop circular utilization of plastics is of manifold significance, yet energy-intensive and poorly selective scission of the ubiquitous carbon-carbon (C-C) bonds in contemporary commercial polymers pose tremendous challenges to envisioned recycling and upcycling scenarios. Here, we demonstrate a topochemical approach for creating elongated C-C bonds with a bond length of 1.57∼1.63 Å between repeating units in the solid state with decreased bond dissociation energies. Elongated bonds were introduced between the repeating units of 12 distinct polymers from three classes. In all cases, the materials exhibit rapid depolymerization via breakage of the elongated bond within a desirable temperature range (140∼260 °C) while otherwise remaining remarkably stable under harsh conditions. Furthermore, the topochemically prepared polymers are processable and 3D-printable while maintaining a high depolymerization yield and tunable mechanical properties. These results suggest that the crystalline polymers synthesized from simple photochemistry and without expensive catalysts are promising for practical applications with complete materials' circularity.

n-type charge transport in heavily p-doped polymers.

It is commonly assumed that charge-carrier transport in doped π-conjugated polymers is dominated by one type of charge carrier, either holes or electrons, as determined by the chemistry of the dopant. Here, through Seebeck coefficient and Hall effect measurements, we show that mobile electrons contribute substantially to charge-carrier transport in π-conjugated polymers that are heavily p-doped with strong electron acceptors. Specifically, the Seebeck coefficient of several p-doped polymers changes sign from positive to negative as the concentration of the oxidizing agents FeCl3 or NOBF4 increase, and Hall effect measurements for the same p-doped polymers reveal that electrons become the dominant delocalized charge carriers. Ultraviolet and inverse photoelectron spectroscopy measurements show that doping with oxidizing agents results in elimination of the transport gap at high doping concentrations. This approach of heavy p-type doping is demonstrated to provide a promising route to high-performance n-type organic thermoelectric materials.

Bioinspired Dynamic Camouflage from Colloidal Nanocrystals Embedded Electrochromics.

Camouflage is often seen in animals, and it presents in both passive and active forms. For instance, the wings of Closterocerus coffeellae exhibit distinct appearances against different backgrounds, while the chameleon actively changes its skin colors to morph into the environment. Herein, we report an artificial skin-like optoelectronic device that enables actively changing appearances and passively morphing into the environment by manipulating light-matter interactions with electrochromic polymers and photonic colloid nanocrystals. To construct the new electrochromic device, highly reflective, yet transmissive photonic nanocrystals are introduced into the gel electrolyte and sandwiched between the layers of electrochromic polymers and ion storage materials. Through voltage-controlled color switching of electrochromic polymers from colored state to bleached state, the degree of light absorbance, transmittance, and reflectance can be finely balanced and precisely modulated with the device. A broad synthesized color gamut and angle-dependent visual effects can be realized on this electronic skin-like device.

Catalytic Synthesis of Conjugated Azopolymers from Aromatic Diazides.

Conjugated polymers containing main chain azoarene repeat units are synthesized by a dinickel catalyzed N=N coupling reaction of aromatic diazides. The polymerization exhibits broad substrate scope and is compatible with heterocycles commonly featured in high performance organic materials, including carbazole, thiophene, propylenedioxythiophene (ProDOT), diketopyrrolopyrrole (DPP), and isoindigo. Copolymerizations can be carried out using monomer mixtures, and monoazide chain stoppers can be used to install well-defined end groups. Azopolymers possess unique properties owing to the functionality of the azo linkages. For example, protonation at nitrogen results in LUMO lowering and red-shifted absorption bands. Additionally, N=N bonds possess low-lying π* levels, allowing azopolymers to be reversibly reduced under mild conditions.

Ambient Oxygen-Doped Conjugated Polymer for pH-Activatable Aggregation-Enhanced Photoacoustic Imaging in the Second Near-Infrared Window.

Photoacoustic (PA) probes absorbing in the second near-infrared (NIR-II: 1000-1700 nm) window hold great promise for deep-tissue diagnosis and treatment. Currently, NIR-II PA probes typically involve complex synthesis and surfactant adjuvant for processing and delivery. Furthermore, these NIR-II PA probes are "always-on," leading to inadequate signal-to-background ratio and low specificity. To address these challenges, this study reports a pH-activatable and aggregation-enhanced NIR-II PA probe. Without using any toxic or exotic oxidants, the selected polymer (PPE) is readily doped by oxygen in an ambient environment and simultaneously red-shifts its absorption profile from visible to NIR-II region. By virtue of the carboxyl groups on the side chains, oxygen-doped PPE is readily water-soluble at a physiological pH but tends to aggregate in an acidic environment. The pH-induced aggregation results in a significant PA enhancement and thus allows specific PA imaging of acidic tumor microenvironment in vivo. Our study provides a facile and surfactant-free strategy for achieving water-soluble and pH-responsive NIR-II PA probes, which could be applied for diagnoses of cancer and other diseases associated with changes in pH. It paves the way for the development of new activatable NIR-II imaging probes and also could facilitate the investigation of biological and pathological processes in deep tissue.

Polymer Electrochromism Driven by Metabolic Activity Facilitates Rapid and Facile Bacterial Detection and Susceptibility Evaluation.

The electrochromism of a water-soluble naturally oxidized electrochromic polymer, ox-PPE, is harnessed for rapid and facile bacterial detection, discrimination, and susceptibility testing. The ox-PPE solution shows distinct colorimetric and spectroscopic changes within 30 min when mixed with live bacteria. For the underlying mechanism, it is found that ox-PPE responds to the reducing species (e.g. cysteine and glutathione) released by metabolically active bacteria. This reduction reaction is ubiquitous among various bacterial strains, with a noticeable difference that enables discrimination of Gram-negative and Gram-positive bacterial strains. Combining ox-PPE with antibiotics, methicillin-susceptible and -resistant S. aureus can be differentiated within 2.5 h. Proof-of-concept demonstration of ox-PPE for antimicrobial susceptibility testing is carried out by incubating E. coli with various antibiotics. The obtained minimum inhibition concentrations are consistent with the conventional culture-based methods, but with the procedure time significantly shortened to 3 h.

Functionalized NIR-II Semiconducting Polymer Nanoparticles for Single-cell to Whole-Organ Imaging of PSMA-Positive Prostate Cancer.

Development of molecular probes holds great promise for early diagnosis of aggressive prostate cancer. Here, 2-[3-(1,3-dicarboxypropyl) ureido] pentanedioic acid (DUPA)-conjugated ligand and bis-isoindigo-based polymer (BTII) are synthesized to formulate semiconducting polymer nanoparticles (BTII-DUPA SPN) as a prostate-specific membrane antigen (PSMA)-targeted probe for prostate cancer imaging in the NIR-II window. Insights into the interaction of the imaging probes with the biological targets from single cell to whole organ are obtained by transient absorption (TA) microscopy and photoacoustic (PA) tomography. At single-cell level, TA microscopy reveals the targeting efficiency, kinetics, and specificity of BTII-DUPA SPN to PSMA-positive prostate cancer. At organ level, PA tomographic imaging of BTII-DUPA SPN in the NIR-II window demonstrates superior imaging depth and contrast. By intravenous administration, BTII-DUPA SPN demonstrates selective accumulation and retention in the PSMA-positive tumor, allowing noninvasive PA detection of PSMA overexpressing prostate tumors in vivo. The distribution of nanoparticles inside the tumor tissue is further analyzed through TA microscopy. These results collectively demonstrate BTII-DUPA SPN as a promising probe for prostate cancer diagnosis by PA tomography.

Recent advances in the use of microcarriers for cell cultures and their ex vivo and in vivo applications.

Microcarriers are 100- to 300-micron support matrices that permit the growth of adherent cells in bioreactor systems. They have a larger surface area to volume ratio in comparison to single cell monolayers, enabling cost-effective cell production and expansion. Microcarriers are composed of a solid matrix that must be separated from expanded cells during downstream processing stages. The detachment method is chosen on the basis of several factors like cell type, microcarrier surface chemistry, cell confluency and degree of aggregation. The development of microcarriers with a range of physiochemical properties permit controlled cell and protein associations that hold utility for novel therapeutics. In this review, we provide an overview of the recent advances in microcarrier cell culture technology. We also discuss its significance as an ex vivo research tool and the therapeutic potential of newly designed microcarrier systems in vivo.

Preparative Mass Spectrometry Using a Rotating-Wall Mass Analyzer.

The design of functional interfaces is central to both fundamental and applied research in materials science and energy technology. We introduce a new, broadly applicable technique for the precisely controlled high-throughput preparation of well-defined interfaces containing polyatomic species ranging from small ions to nanocrystals and large protein complexes. The mass-dispersive deposition of ions onto surfaces is achieved using a rotating-wall mass analyzer, a compact device which enables the separation of ions using low voltages and has a theoretically unlimited mass range. We demonstrate an efficient deposition of singly charged Au144 (SC4 H9 )60 ions (33.7 kDa), which opens up exciting opportunities for the structural characterization of nanocrystals and their assemblies using transmission electron microscopy. Our approach also enables the high-throughput deposition of mass-selected ions from multicomponent mixtures, which is of interest to the controlled preparation of surface gradients and rapid screening of molecules in mixtures for a specific property.

Catalytic Azoarene Synthesis from Aryl Azides Enabled by a Dinuclear Ni Complex.

Azoarenes are valuable chromophores that have been extensively incorporated as photoswitchable elements in molecular machines and biologically active compounds. Here, we report a catalytic nitrene dimerization reaction that provides access to structurally and electronically diverse azoarenes. The reaction utilizes aryl azides as nitrene precursors and generates only gaseous N2 as a byproduct. By circumventing the use of a stoichiometric redox reagent, a broad range of organic functional groups are tolerated, and common byproducts of current methods are avoided. A catalyst featuring a Ni-Ni bond is found to be uniquely effective relative to those containing only a single Ni center. The mechanistic origins of this nuclearity effect are described.

Critical Role of Surface Energy in Guiding Crystallization of Solution-Coated Conjugated Polymer Thin Films.

It is well-known that substrate surface properties have a profound impact on the morphology of thin films solution coated atop and the resulting solid-state properties. However, design rules for guiding the substrate selection have not yet been established. Such design rules are particularly important for solution-coated semiconducting polymers, as the substrate-directed thin film morphology can impact charge transport properties by orders of magnitude. We hypothesize that substrate surface energies dictate the thin film morphology by modulating the free energy barrier to heterogeneous nucleation. To test this hypothesis, we systematically vary the substrate surface energy via surface functionalization techniques. We perform in-depth morphology and device characterizations to establish the relationship between substrate surface energy, thin film morphology and charge transport properties, employing donor-acceptor (D-A) conjugated polymers. We find that decreasing the substrate surface energy progressively increases thin film crystallinity, degree of molecular ordering, and extent of domain alignment. Notably, the enhanced morphology on the lowest surface energy substrate leads to a 10-fold increase in the charge carrier mobility. We further develop a free energy model relating the substrate surface energy to the penalty of heterogeneous nucleation from solution in the thin film geometry. The model correctly predicts the experimental trend, thereby validating our hypothesis. This work is a significant step toward establishing design rules and understanding the critical role of substrates in determining morphology of solution-coated thin films.

Hierarchical N-Doped Carbon as CO2 Adsorbent with High CO2 Selectivity from Rationally Designed Polypyrrole Precursor.

Carbon capture and sequestration from point sources is an important component in the CO2 emission mitigation portfolio. In particular, sorbents with both high capacity and selectivity are required for reducing the cost of carbon capture. Although physisorbents have the advantage of low energy consumption for regeneration, it remains a challenge to obtain both high capacity and sufficient CO2/N2 selectivity at the same time. Here, we report the controlled synthesis of a novel N-doped hierarchical carbon that exhibits record-high Henry's law CO2/N2 selectivity among physisorptive carbons while having a high CO2 adsorption capacity. Specifically, our synthesis involves the rational design of a modified pyrrole molecule that can co-assemble with the soft Pluronic template via hydrogen bonding and electrostatic interactions to give rise to mesopores followed by carbonization. The low-temperature carbonization and activation processes allow for the development of ultrasmall pores (d < 0.5 nm) and preservation of nitrogen moieties, essential for enhanced CO2 affinity. Furthermore, our described work provides a strategy to initiate developments of rationally designed porous conjugated polymer structures and carbon-based materials for various potential applications.

Effect of Broken Conjugation on the Stretchability of Semiconducting Polymers.

Increasing the flexibility of polymer chains is a common method of increasing the deformability of solid polymeric materials. Here, the effects of "conjugation-break spacers" (CBSs)-aliphatic units that interrupt the sp2 -hybridized backbone of semiconducting polymers-on the mechanical and photovoltaic properties of a diketopyrrolopyrrole-based polymer are described. Unexpectedly, the tensile moduli and cracking behavior of a series of polymers with repeat units bearing 0%, 30%, 50%, 70%, and 100% of the CBS are not directly related to the percent incorporation of the flexible unit. Rather, the mechanical properties are a strong function of the order present in the film as determined by grazing-incidence x-ray diffraction. The effect of the CBSs on the photovoltaic performance of these materials, on the other hand, is more intuitive: it decreases with increasing fraction of the flexible units. These studies highlight the importance of solid-state packing structure-as opposed to only the flexibility of the individual molecules-in determining the mechanical properties of a conjugated polymer film for stretchable, ultraflexible, and mechanically robust electronics.

Chiroptical Switching of Electrochromic Polymer Thin Films.

The interaction between light and chiroptical polymers plays a crucial role in chiroptics, spintronics, and chiral-spin selectivity. Despite considerable successes in creating dissymmetric polymer films, the elucidation of chiroptical activities under electrochemical switching remains unexplored. Here homogeneous chiral electrochromics is reported using chiral assembly of conjugated polymers through a transient solidification process with molecular chiral templates. In their neutral state, the chiral electrochromic polymers directly produce a remarkably dissymmetric polarization-dependent transmittance. The circular dichroism (CD) and dissymmetric transmission can be tuned by adjusting the doping level of the electrochemically active polymer films. Under high levels of oxidation, the chiroptical activities are reversed with strong bleaching in the visible, leading to formation of monosignate CD spectra over the infrared region. The matching between circular polarization handedness and chirality of chiroptical polymers makes a distinct impact on optical contrast and color switching dynamics due to the flipped chiroptical activities through polymer redox reactions. The differential circularly polarized transmission in the chiral see-through display can make a well-resolved color change in human eyes, demonstrating proof-of-concept devices for 3D imaging and information encryption. This work serves as a foundation to develop advanced on-chip fabrication of circular polarization-multiplexed display in flexible and highly integrated platforms.

Transparent Electrochromic Polymers with High Optical Contrast and Contrast Ratio.

Colored-to-transmissive electrochromic polymers, known for their wide selection of colors and solution processability, have gained great attraction in thin film electrochromic devices that have entered the market. However, their adoption in the real world is limited due to their limited optical transparency and contrast. This study introduces a new molecular design strategy to overcome these issues. This strategy involves using meta-conjugated linkers (MCLs) and aromatic moieties along polymer backbones, which enable transparent-to-colored electrochromic switching. The MCL interrupts charge delocalization, increasing the band gap in the neutral state and ensuring transparency in the visible region. This innovative approach achieves nearly 100% transmittance in the neutral state and a high absorption in the oxidized state, overcoming residue absorption issues in conventional electrochromic polymers. Simultaneously, the MCL and aromatic moieties enable low oxidation potential, facilitating stable transparent-to-color switching. Polymers developed using this approach exhibit wide color tunability, optical contrast exceeding 93%, and cycling stability over 5000 cycles with less than 3% contrast decay. Our research represents a major advancement in overcoming existing challenges, enabling polymer-based electrochromic devices for visual comfort and energy conservation.