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We report a versatile new synthetic route to poly(para-phenylene)s (PPPs) and related poly(para-arylene)s containing high degrees of substitution not readily available by other methods. Our method transforms highly soluble, alkyne-containing polymers into PPPs via high-yielding, transition metal-mediated [2+2+2] cyclizations., National Science Foundation (U.S.) (Grant DMR-1005810)

© 2019 The Royal Society of Chemistry. Stimuli-responsive supramolecular assemblies are dynamic systems that can reversibly switch between different states upon external stimuli. In this context, metal coordination offers a reliable strategy for the preparation of stimuli responsive supramolecular architectures. Herein we report the preparation of a solvent-responsive cavitand-lanthanum coordination complex. A tetra-phosphonate cavitand has been functionalized with four hydroxyl moieties at the upper rim to form a pre-organized octadentate ligand capable of binding lanthanum salts. Exploiting the orthogonal recognition sites, two different complex architectures are formed in acetonitrile and acetone, respectively. The complexes have been characterized in solution by NMR spectroscopy, ITC experiments, while at the solid state, the single crystal structure of the acetonitrile derivative has been determined. Furthermore, as observed by DOSY-NMR spectroscopy, small quantities of acetone in acetonitrile are sufficient to trigger assembly interconversion.

Incorporating fluorine atoms into a molecule can endow it with various unique properties that enable materials applications. Selective solubility in fluorous solvents is achieved by a high fluorine content and selective partitioning into perfluorinated liquids over organic and aqueous phases provides orthogonal opportunities for chemistry and materials assembly. Although there is a growing number of partially fluorinated molecules, there are insufficient structural design principles to produce diverse fluorous soluble dyes. Herein, we report the synthesis of six fluorous phthalocyanine and subphthalocyanine dyes, and study their properties in the fluorous phase. Phthalocyanines generally display limited solubility and we also observed apparent aggregation in the fluorous phase. However, the nonplanar subphthalocyanines showed greater solubility. Subphthalocyanines also displayed fluorescence in selected solvents, and their emissive properties were investigated. The materials described expand the library of fluorous dyes and provide insights for the design of new molecules with fluorous solubility.

Copyright © 2020 American Chemical Society. Despite the recent emergence of microcavity resonators as label-free biological and chemical sensors, practical applications still require simple and robust methods to impart chemical selectivity and reduce the cost of fabrication. We introduce the use of hydrocarbon-in-fluorocarbon-in-water (HC/FC/W) double emulsions as a liquid top cladding that expands the versatility of optical resonators as chemical sensors. The all-liquid complex emulsions are tunable droplets that undergo dynamic and reversible morphological transformations in response to a change in the chemical environment (e.g., exposure to targeted analytes). This chemical-morphological coupling drastically modifies the effective refractive index, allowing the complex emulsions to act as a chemical transducer and signal amplifier. We detect this large change in the refractive index by tracking the shift of the enveloped resonant spectrum of a silicon nitride (Si3N4) racetrack resonator-based sensor, which correlates well with a change in the morphology of the complex droplets. This combination of soft materials (dynamic complex emulsions) and hard materials (on-chip resonators) provides a unique platform for liquid-phase, real-time, and continuous detection of chemicals and biomolecules for miniaturized and remote, environmental, medical, and wearable sensing applications.

© 2019 The Royal Society of Chemistry. We report on a new modular sensing approach in which complex emulsions serve as efficient transducers in optical evanescent field-based sensing devices. Specifically, we leverage the tunable refractive index upon chemically triggered changes in droplet morphology or orientation. Variations in the optical coupling result in readily detectable changes in the light transmitted from a waveguide.

Efficient syntheses that incorporate thiophene units into different extended conjugation systems are of interest as a result of the prevalence of sulfur-rich aromatics in organic electronics. Self-organization by using liquid crystal properties is also desirable for optimal processing of organic electronics and optical devices. In this article, we describe a two-step process to access extended regioisomers of polyaromatics with different shapes. This method involves an efficient single or double benzannulation from an alkyne precursor followed by Scholl cyclization. In spite of their unconventional nondiscoid shape, these materials display stable columnar liquid crystal phases. We examine the photophysical and electrochemical properties and find that structurally very similar thiophene-fused polyaromatics display significant differences in their properties., Swiss National Science Foundation (Award P2ELP2_165170), Minister of Science and Technology, Taiwan (Award 106-2917-I-564-058), National Institutes of Health (Award F32 GM126643), Air Force Office of Scientific Research (Grant FA9550-18-1-0341)

Square planar platinum(II) thienyl pyridyl complexes with board-shaped structures assemble into lamellar (SmA) liquid crystal phases at elevated temperatures. Liquid crystals of this type are expected to have stronger biaxial correlations than typical calamitic mesogens. The mesophase stability improves with decreasing alkyl chain lengths with C₈H₁₇ having the widest range of stability. All complexes are luminescent in solution., National Science Foundation (U.S.) (Grant DMR-1410718)

Poly(p-phenylene sulfide) (PPS) is a highly robust thermoplastic with outstanding thermal and chemical stability. However, development of functional PPS-based materials is hampered by harsh synthetic conditions and poor solubility. As an alternative to nucleophilic aromatic substitution (SNAr), we report herein on the use of benzoquinone conjugate addition chemistry to prepare PPS derivatives bearing redox-active hydroquinones in the polymer backbone. Specifically, we utilize thiosilanes as thiol surrogates to attenuate unproductive redox isomerization reactions and to provide a thermodynamic driving force for polymerization. The silyl transfer conjugate addition process results in a poly(phenylene silylhydroquinone sulfide) (PPSHS) amenable to several divergent modes of functionalization. Notably, the so-formed PPSHS exists as gels, which swell organic solvents and exhibit distinct changes in color and swelling upon redox changes. By repeated cycling of oxidation and thiol conjugate addition, the cross-linked networks can be depolymerized under ambient conditions. Finally, we prepared an interpenetrating polymer network (IPN) composed of PPSHS and cross-linked poly(n-butyl acrylate), which exhibits a significant enhancement in thermomechanical properties over the base materials., NIH (Award F32 GM126643-02)

Complex liquid colloids hold great promise as transducers in sensing applications as a result of their tunable morphology and intrinsic optical properties. Herein, we introduce meta-amino substituted green fluorescence protein chromophore (GFPc) surfactants that localize at the organic-water interface of complex multiphase liquid colloids. The meta-amino GFPc exhibits hydrogen-bonding (HB) mediated fluorescence quenching, and are nearly nonemissive in the presence of protic solvents. We demonstrate morphology-dependent fluorescence of complex liquid colloids and investigate the interplay between GFPc surfactants and other simple surfactants. This environmentally responsive surfactant allows us to observe morphological changes of complex emulsions in randomized orientations. We demonstrate utility with an enzyme activity based fluorescence "turn-ON" scheme. The latter employs an oligopeptide-linked GFPc that functions as both a surfactant and trypsin target. The cleavage of hydrophilic peptide results in a morphology change and ultimately a fluorescence turn-on. Fluorescent complex colloids represent a new approach for biosensing in liquid environments., National Institutes of Health of General Medical Sciences (Grant GM095843)

Here we report a sensing method for Listeria monocytogenes based on the agglutination of all-liquid Janus emulsions. This two-dye assay enables the rapid detection of trace Listeria in less than 2 h via an emissive signal produced in response to Listeria binding. The biorecognition interface between the Janus emulsions is assembled by attaching antibodies to a functional surfactant polymer with a tetrazine/transcyclooctene click reaction. The strong binding between Listeria and the Listeria antibody located at the hydrocarbon surface of the emulsions results in the tilting of the Janus structure from its equilibrium position to produce emission that would ordinarily be obscured by a blocking dye. This method provides rapid and inexpensive Listeria detection with high sensitivity (<100 CFU/mL in 2 h) that can be paired with many antibody or related recognition elements to create a new class of biosensors., Department of Defense (Grant N000141812878)

Single-walled carbon nanotubes (SWCNTs) are recognized as versatile materials for the formation of chemiresistive sensors. However, imparting high sensitivity and selectivity to SWCNTs remains a major challenge. Herein, we report a new sensory system that interfaces SWCNTs and catalytic metal nanoparticles (NPs) in a film of a porous ion exchange polymer to produce sensitive and selective sensors. The porous polymer films are based on imidazolium-functionalized triptycene polyether sulfone, and the environment created by this polymer results in the formation of ultrasmall (<5 nm) Au NPs. The polymer serves to suppress the growth of Au NPs while maintaining gas transport. The size control promotes strong interactions between Au NPs and carbon monoxide (CO), and this composition produces a robust, sensitive, and selective CO chemiresistive sensor. We further demonstrate that the modulation of a gate voltage in chemical field-effect transistor sensing devices enhances the performance by promoting the activity of Au NPs. The sensors display an increase of CO response at room temperature in air under the negative gate voltage. Our results demonstrate that the combination of a porous ion exchange matrix, NPs, and gate voltage-modulated chemiresistors can be synergistically tuned to create sensitive and selective sensors for target analytes., National Science Foundation (Grant DMR-1809740)

Controlled, dynamic movement of materials through noncontacting forces provides interesting opportunities in systems design. Confinement of magnetic nanoparticles to the interfaces of double emulsions introduces exceptional control of double emulsion movement. We report the selective magnetic functionalization of emulsions by the in situ selective reactions of amine-functionalized magnetic nanoparticles and oil-soluble aldehydes at only one of the double emulsion's interfaces. We demonstrate morphology-dependent macroscopic ferromagnetic behavior of emulsions induced by the interfacial confinement of the magnetic nanoparticles. The attraction and repulsion of the emulsions to applied magnetic fields results in controlled orientation changes and rotational movement. Furthermore, incorporation of liquid crystals into the double emulsions adds additional templating capabilities for precision assembly of magnetic nanoparticles, both along the interface and at point defects. Applying a magnetic field to liquid crystal complex emulsions can produce movement as well as reorganization of the director field in the droplets. The combination of interfacial chemistry and precise assembly of magnetic particles creates new systems with potentially useful field-responsive properties., Department of Defense (Grant N000141812878)

We report a new class of dynamically reconfigurable complex colloids comprising immiscible liquid crystals (LCs) and fluorocarbon oils. Producing stable spherical droplets requires the utilization of appropriately designed surfactants to reduce the high intrinsic surface tension between the LCs and the fluorocarbon oils that initially lead to nonspherical, "snowman-shaped" Janus droplets. After stabilizing the interfaces via surfactants, the LC droplet morphology can be dynamically switched between LC-in-fluorocarbon-in-water double emulsions (LC/F/W), spherical Janus emulsions, and inverted double emulsions (fluorocarbon-in-LC-in-water, F/LC/W) in response to changes in the surrounding surfactants. These stabilization methods can be extended to smectic LCs to create droplets with more complex internal arrangements and expand the range of LC emulsions that can be prepared. In addition, by using new mesogenic surfactants that control the LC director field at each LC interface, we prepare LC complex colloids exhibiting different internal configurations. The ability to control the LC anchoring conditions made it possible to create topological singularities as powerful templates for the precision assembly of antibodies at the droplets' interface. These dynamic LC complex colloids of controllable morphology and LC orientation are rich soft material platforms that will find utility in a variety of sensing applications., Department of Defense (Grant N000141812878)

Fluid-like sliding graphenes but with solid-like out-of-plane compressive rigidity offer unique opportunities for achieving unusual physical and chemical properties for next-generation interfacial technologies. Of particular interest in the present study are graphenes with specific chemical functionalization that can predictably promote adhesion and wetting to substrate and ultralow frictional sliding structures. Lubricity between stainless steel (SS) and diamond-like carbon (DLC) is experimentally demonstrated with densely functionalized graphenes displaying dynamic intersheet bonds that mechanically transform into stable tribolayers. The macroscopic lubricity evolves through the formation of a thin film of an interconnected graphene matrix that provides a coefficient of friction (COF) of 0.01. Mechanical sliding generates complex folded graphene structures wherein equilibrated covalent chemical linkages impart rigidity and stability to the films examined in macroscopic friction tests. This new approach to frictional reduction has broad implications for manufacturing, transportation, and aerospace., National Science Foundation (Grant DMR‐1809740)

Orthogonal functionalization of 2D materials by selective assembly at interfaces provides opportunities to create new materials with transformative properties. Challenges remain in realizing controllable, scalable surface-selective, and orthogonal functionalization. Herein, dynamic covalent assembly is reported that directs the functionalization of graphene surfaces at liquid–liquid interfaces. This process allows facile addition and segregation of chemical functionalities to impart Janus characteristics to graphenes. Specifically, dynamic covalent functionalization is accomplished via Meisenheimer complexes produced by reactions of primary amines with pendant dinitroaromatics attached to graphenes. Janus graphenes are demonstrated to be powerful surfactants that organize at water/organic, water/fluorocarbon, and organic/fluorocarbon liquid interfaces. This approach provides general access to the creation of diverse surfactant materials and promising building blocks for 2D materials.

Dynamically reconfigurable oil-in-water (o/w) Pickering emulsions are developed, wherein the assembly of particles (i.e., platinum-on-carbon and iron-on-carbon particles) can be actively controlled by adjusting interfacial tensions. A balanced adsorption of particles and surfactants at the o/w interface allows for the creation of inhomogeneity of the particle distribution on the emulsion surface. Complex Pickering emulsions with highly controllable and reconfigurable morphologies are produced in a single step by exploiting the temperature-sensitive miscibility of hydrocarbon and fluorocarbon liquids. Dynamic adsorption/desorption of (polymer) surfactants afford both shape and configuration transitions of multiple Pickering emulsions and encapsulated core/shell structured can be transformed into a Janus configuration. Finally, to demonstrate the intrinsic catalytic or magnetic properties of the particles provided by carbon bound Pt and Fe nanoparticles, two different systems are investigated. Specifically, the creation of a bimetallic microcapsule with controlled payload release and precise modulation of translational and rotational motions of magnetic emulsions are demonstrated, suggesting potential applications for sensing and smart payload delivery., National Research Foundation (Grant 2018R1D1A1B07040671 and 2016R1E1A1A02921128)

Stimuli-responsive materials offer new opportunities to resolve long-standing material challenges and are rapidly gaining pivotal roles in diverse applications. For example, smart protective garments that rapidly transport water vapor and autonomously block chemical threats are expected to enable an effective new paradigm of adaptive personal protection. However, the incorporation of these seemingly incompatible properties into a single responsive system remains elusive. Herein, a bistable membrane that can rapidly, selectively, and reversibly transition from a highly breathable state in a safe environment to a chemically protective state when exposed to organophosphate threats such as sarin is demonstrated. Dynamic response to chemical stimuli is achieved through the physical collapse of an ultrathin copolymer layer on the membrane surface, which efficiently gates transport through membrane pores composed of single-walled carbon nanotubes (SWNTs). The adoption of nanometer-wide SWNTs for ultrafast moisture conduction enables a simultaneous boost in size-sieving selectivity and water-vapor permeability by decreasing nanotube diameter, thereby overcoming the breathability/protection trade-off that limits conventional membrane materials. Adaptive multifunctional membranes based on this platform greatly extend the active use of a protective garment and present exciting opportunities in many other areas including separation processes, sensing, and smart delivery.

© 2020 World Scientific Publishing Company. Incorporating fluorine atoms into a molecule can endow it with various unique properties that enable materials applications. Selective solubility in fluorous solvents is achieved by a high fluorine content and selective partitioning into perfluorinated liquids over organic and aqueous phases provides orthogonal opportunities for chemistry and materials assembly. Although there is a growing number of partially fluorinated molecules, there are insufficient structural design principles to produce diverse fluorous soluble dyes. Herein, we report the synthesis of six fluorous phthalocyanine and subphthalocyanine dyes, and study their properties in the fluorous phase. Phthalocyanines generally display limited solubility and we also observed apparent aggregation in the fluorous phase. However, the nonplanar subphthalocyanines showed greater solubility. Subphthalocyanines also displayed fluorescence in selected solvents, and their emissive properties were investigated. The materials described expand the library of fluorous dyes and provide insights for the design of new molecules with fluorous solubility.

Materials with magneto-optic (MO) properties have enabled critical fiber-optic applications and highly sensitive magnetic field sensors. While traditional MO materials are inorganic in nature, new generations of MO materials based on organic semiconducting polymers could allow increased versatility for device architectures, manufacturing options, and flexible mechanics. However, the origin of MO activity in semiconducting polymers is far from understood. In this paper, we report high MO activity observed in a chiral helical poly-3-(alkylsulfone)thiophene (P3AST), which confirms a new design for the creation of a giant Faraday effect with Verdet constants up to (7.63 ± 0.78) × 104 deg T-1 m-1 at 532 nm. We have determined that the sign of the Verdet constant and its magnitude are related to the helicity of the polymer at the measured wavelength. The Faraday rotation and the helical conformation of P3AST are modulated by thermal annealing, which is further supported by DFT calculations and MD simulations. Our results demonstrate that helical polymers exhibit enhanced Verdet constants and expand the previous design space for polythiophene MO materials that was thought to be limited to highly regular lamellar structures. The structure-property studies herein provide insights for the design of next-generation MO materials based upon semiconducting organic polymers.

Here we report an efficient synthesis of optically active ladder-type molecules and polymers through intramolecular cyclization of chiral triptycenes containing bis[2-(4-alkoxyphenyl)ethynyl]phenylene units. The electrophile-induced cyclization reactions are directed away from the bridgehead carbon atoms of triptycene by steric factors, thereby producing one-handed twisted ladder units without any detectable byproducts. Moreover, the quantitative and regioselective nature of this intramolecular cyclization allowed us to synthesize optically active ladder polymers with a well-defined one-handed helical geometry in which homoconjugated dibenzo[a,h]anthracene units are helically arranged along the main chain. This synthesis route enables the construction of a variety of nanoscale helical ladder architectures and provides an entry into new chiroptical materials., Air Force Office of Scientific Research (Grant 17RT0904)

Ethylene is a dynamic plant hormone, and its temporal monitoring can be used to glean insight into plant health and status. However, the real-time distributed detection of ethylene at trace levels under ambient conditions remains a challenge. We report a single-walled carbon nanotube-based chemiresistor catalyst combination that can detect ppb levels of ethylene in air. Cycling between Pd(II) and Pd(0) via Wacker oxidation with a nitrite cocatalyst imparts response discrimination driven by the chemoselectivity of the chemical transformation. Sensitivity is controlled by a combination of the chemical reaction efficiency and the n-doping strength of the Pd(0) species generated in situ. The covalent functionalization of the carbon nanotube sidewall with pyridyl ligands drastically improves the device sensitivity via enhanced n-doping. The utility of this ethylene sensor is demonstrated in the monitoring of senescence in red carnations and purple lisianthus flowers., U.S. Army Engineer Research and Development Center Environmental Quality Technology Program (Contract W912HZ-17-2-0027), National Science Foundation (Grant DMR-1809740)

Investigations of magnetism in electronically coupled polyradicals have largely focused on applications in photonic and magnetic devices, wherein radical polymers were found to possess molecularly tunable and cooperative magnetic properties. Radical polymers with nonconjugated insulating backbones have been intensively investigated previously; however the integration of radical species into conducting polymer backbones is at an early stage. We report herein 1,3-bisdiphenylene-2-phenylallyl (BDPA)-based conjugated radical polymers that display ambipolar redox activities and conductivities. Moreover, these radical polymers were demonstrated to be promising magneto-optic (MO) materials with Faraday rotations wherein the sign is modulated by the radical character and display absolute Verdet constants up to (2.80 ± 0.84) × 104 deg T-1 m-1 at 532 nm. These values rival the performance of the present-day commercial inorganic MO materials (e.g., terbium gallium garnet, V = -1.0 × 104 deg T-1 m-1 at 532 nm). The structure property studies detailed herein reveal the promise of multifunctional conjugated radical polymers as responsive MO materials.

A modular and facile route has been developed to synthesize functionalized 2,5-di(thiophen-2-yl)-1-H-arylpyrroles from readily available starting materials. These units are compatible with various polymerization conditions and are versatile building blocks for conjugated polymers. The polymers show high thermal stability and solubility in a number of solvents. Characterization of the polymers reveals a correlation between molecular packing, controllable by polymer design, and charge carrier mobility.

Full-color reflective photonic ellipsoidal polymer particles, capable of a dynamic color change, are created from dendronized brush block copolymers (den-BBCPs) self-assembled by solvent-evaporation from an emulsion. Surfactants composed of dendritic monomer units allow for the precise modulation of the interfacial properties of den-BBCP particles to transition in shape from spheres to striped ellipsoids. Strong steric repulsions between wedge-type monomers promote rapid self-assembly of polymers into large domains (i.e., 153 nm ≤ D ≤ 298 nm). Of note, highly ordered axially stacked lamellae (i.e., number of layers >100) within an ellipsoid give rise to a near-perfect photonic multilayer. The reflecting color is readily tunable across the entire visible spectrum by alteration of the molecular weight from 477 to 1144 kDa. Finally, the photonic ellipsoids are functionalized with magnetic nanoparticles organized into bands on the particle surface to produce real-time on/off coloration by magnetic field-assisted activation. In total, the reported photonic ellipsoidal particles represent a new class of switchable photonic materials., Department of Defense (Grant N000141812878)

Perfluorinated liquids can exhibit immiscibility with organic solvents and water, and provide orthogonal opportunities in chemistry. Examples of emissive dyes that display only fluorous phase solubility are limited, despite the many potential applications. Perylene bisimides are among the most versatile dyes and are known for their outstanding stability and high quantum yields. Herein, we report the synthesis of two new fluorofluorescent perylene bisimide dyes, designed to be soluble in the fluorous phases. These two dyes possess unique photophysical properties, including dramatic increases in fluorescence quantum yields when treated with Bronsted acids as well as aggregation in the fluorous phase.