Structure and stability of polydiacetylene membrane systems: Molecular dynamics simulation studies

We have performed full atomistic molecular dynamics (MD) simulations to investigate structure and stability of bilayer membrane systems consisting of monomeric or polymeric 10,12-pentacosadiynoic acid (PCDA) units connected with lysine groups by amide bonds. The PCDA monomer molecules show a twisted three-rod-domain structure with two kinks but upon polymerization, they possess more elongated conformation. The resulting polydiacetylene (PDA) membrane systems have stable membrane structures at room temperature, which is similar to biological lipid bilayer membranes and maintain their gel-like membrane integrity even up to as high as 370 K. Structural properties such as area per monomer, membrane thickness, density profile, 2D pair distribution function, and orientational correlation function are also calculated to understand the membrane structure and check its stability upon thermal fluctuation with atomistic resolution. This study is expected to provide the understanding about PDA membrane systems in atomistic details as well as significant insights into designing new novel PDA sensors.

[Development of External Stimuli-responsive Organic π Molecules and the Creation of Novel Photo-functions]

We have found that the spiro form of aminobenzopyranoxanthene (ABPX) exhibits dual solvatochromic and nanoaggregate fluorescence in organic solvents by spectrophotometric and theoretical analyses. The dual fluorescence properties of ABPX were adjustable in response to water content, and served as a new detection principal for naked-eye visualization (above 0.5 wt%) and quantification (0.010-0.125 wt%) of water in tetrahydrofuran. In investigating the optical properties of a dicationic form of ABPX, ABPX containing linear n-alkyl chains at amino groups were then synthesized. These ABPX exhibited fluorescence emission in the far-red and NIR wavelength regions, and we noted an increased fluorescence quantum efficiency with increasing n-alkyl chain length. To further improve the fluorescence quantum yields, we have designed and synthesized ABPX with different nitrogen-containing fused rings. It was kinetically demonstrated that the structurally rigid conjugation of the xanthene moiety is an effective molecular design for the drastic enhancement of fluorescence emission efficiency.

Recent Advances of the Polymer Micro/Nanofiber Fluorescence Waveguide

Subwavelength optical micro/nanofibers have several advantages, such as compact optical wave field and large specific surface area, which make them widely used as basic building blocks in the field of micro-nano optical waveguide and photonic devices. Among them, polymer micro/nanofibers are among the first choices for constructing micro-nano photonic components and miniaturized integrated optical paths, as they have good mechanical properties and tunable photonic properties. At the same time, the structures of polymer chains, aggregated structures, and artificial microstructures all have unique effects on photons. These waveguided micro/nanofibers can be made up of not only luminescent conjugated polymers, but also nonluminous matrix polymers doped with luminescent dyes (organic and inorganic luminescent particles, etc.) due to the outstanding compatibility of polymers. This paper summarizes the recent progress of the light-propagated mechanism, novel design, controllable fabrication, optical modulation, high performance, and wide applications of the polymer micro/nanofiber fluorescence waveguide. The focus is on the methods for simplifying the preparation process and modulating the waveguided photon parameters. In addition, developing new polymer materials for optical transmission and improving transmission efficiency is discussed in detail. It is proposed that the multifunctional heterojunctions based on the arrangement and combination of polymer-waveguided micro/nanofibers would be an important trend toward the construction of more novel and complex photonic devices. It is of great significance to study and optimize the optical waveguide and photonic components of polymer micro/nanofibers for the development of intelligent optical chips and miniaturized integrated optical circuits.

Tuning of the Topochemical Polymerization of Diacetylenes Based on an Odd/Even Effect of the Peripheral Alkyl Chain: Thermochromic Reversibility in a Thin Film and a Single-Component Ink for a Fountain Pen

The topochemical polymerization of diacetylenes (DAs) is closely related to the length of their alkyl chain. DA monomers have two types of alkyl chain side groups: the inner alkyl chain and the outer alkyl chain, that is, the peripheral alkyl chain. Herein, we designed and synthesized a series of DA monomers that possess bis-amide linkages with different peripheral alkyl chains ( n = 6-9; DA1-DA4). The peripheral alkyl chain length of these DA monomers exhibits an odd/even effect on topochemical polymerization. The polymerization of DAs was achieved only when n is an odd number, whereas no polymerization occurred when n is an even number. The odd/even effect on the topochemical polymerization was also investigated using ab initio density functional theory calculations. The thermochromic reversibility of polydiacetylenes (PDAs) was investigated using UV-vis absorption spectroscopy at temperatures ranging from 20 to 60 °C. Monomer DA2 was used as a single-component ink solution in a fountain pen that can be transformed into thermochromic letters on conventional paper. Furthermore, a PDA-embedded polyethylene oxide film was included to monitor the thermochromic reversibility and was found to exhibit excellent thermochromic reversibility between 20 and 100 °C and stability, enabling storage for a few months without deformation. Finally, a green-colored patterned polymer film is readily obtained by a subtractive color (blue and yellow) mixing method and exhibits high thermochromic reversibility at temperatures between 20 and 100 °C.

Polydiacetylene Nanofiber Composites as a Colorimetric Sensor Responding To Escherichia coli and pH

Polydiacetylenes (PDAs) are conjugative polymers that demonstrate color changes as a response to an external stimulus. In this study, 10,12-pentacosadiynoic acid (PCDA) was mixed with a supporting polymer including poly(ethylene oxide) (PEO) and polyurethane (PU), and the mixture solution was electrospun to construct fiber composites. The electrospun fibers were then photopolymerized using UV irradiation to produce PEO-PDA and PU-PDA nanofiber mats with a fiber diameter ranging from 130 nm to 2.5 μm. The morphologies of both PEO-PDA and PU-PDA nanofibers were dependent on electrospinning parameters such as the ratio of PCDA to PEO or PCDA to PU and the total polymer concentrations. Scanning electron microscopy images showed beaded fibers of PEO-PDA and PU-PDA at 2 and 18 w/v % concentrations, respectively. Smooth fibers were found when the solvent concentration was increased to 3.75 w/v % in PEO-PDA and 25 w/v % in PU-PDA fibers. Both PEO-PDA and PU-PDA nanofiber composites demonstrated excellent colorimetric responses to the presence of Escherichia coli ATCC25922 bacterial cells and the changes in pH as external stimuli. The nanofibers underwent a rapid colorimetric response when exposed directly to E. coli ATCC25922 grown on Luria-Bertani agar. The comparison between the PEO-PDA and PU-PDA suggested that the combination of PEO and PDA is favorable because it provides a sensitive response to the presence of E. coli. The results were compared with samples of a PDA polymer in the absence of a matrix polymer. The colorimetric response was similar when the PDA polymer and the PDA nanofiber composites were exposed to pH changes, and the color change was found to occur at pH 10 and enhanced at pH 11-13. The PDA-containing nanofiber composites showed stronger colorimetric responses than those of the PDA polymer only, suggesting their potential as biosensors and chemosensors.

Advances in polydiacetylene development for the design of side chain groups in smart material applications – a mini review

This review focuses on various side chain groups based on PDAs published over the last 3 years, covering urea, melamine, ferriferous oxide and coumarin. Perspectives on the remaining challenges and future developments are also proposed.

Flexible and stretchable chromatic fibers with high sensing reversibility

Chromatic polymers, such as polydiacetylene (PDA) that display color changes under stimulations, have been widely explored as sensors and displays. However, the PDA-based materials are generally rigid and irreversible in the chromatic transition. Herein, a flexible and stretchable PDA composite fiber is produced by incorporating peptide-modified PDA into aligned carbon nanotubes on an elastic fiber substrate. It performs a rapid and reversible chromatic transition in response to electrical current that can be repeated for 1000 cycles without fatigue. Due to their high flexibility and stretchability, these chromatic fibers can be integrated into different patterns and woven into smart textiles for displaying and sensing applications.

A Magnetically Responsive Polydiacetylene Precursor for Latent Fingerprint Analysis

A magnetically responsive diacetylene (DA) powder was developed for the visualization of latent fingerprints. A mixture of the DA and magnetite nanoparticles, applied to a surface containing latent fingermarks, becomes immobilized along the ridge patterns of the fingerprints when a magnetic field is applied. Alignment along the ridge structures is a consequence of favorable hydrophobic interactions occurring between the long alkyl chains in the DAs and the lipid-rich, sebaceous latent fingermarks. UV irradiation of the DA-magnetite composite immobilized on the latent fingerprint results in the generation of blue-colored PDAs. Heat treatment of the blue-colored image promotes a blue-to-red transition as well as fluorescence turn-on. A combination of the aligned pale brown-colored monomeric state, UV irradiation generated blue-colored PDA state, as well as the heat treatment generated red-colored and fluorescent PDA state enables efficient visual imaging of a latent fingerprint, which is deposited on various colored solid surfaces.

Controlled Phase and Tunable Magnetism in Ordered Iron Oxide Nanotube Arrays Prepared by Atomic Layer Deposition

Highly-ordered and conformal iron oxide nanotube arrays on an atomic scale are successfully prepared by atomic layer deposition (ALD) with controlled oxidization states and tunable magnetic properties between superparamagnetism and ferrimagnetism. Non-magnetic α-Fe₂O₃ and superparamagnetic Fe₃O₄ with a blocking temperature of 120 K are in-situ obtained by finely controlling the oxidation reaction. Both of them exhibit a very small grain size of only several nanometers due to the nature of atom-by-atom growth of the ALD technique. Post-annealing α-Fe₂O₃ in a reducing atmosphere leads to the formation of the spinel Fe₃O₄ phase which displays a distinct ferrimagnetic anisotropy and the Verwey metal-insulator transition that usually takes place only in single crystal magnetite or thick epitaxial films at low temperatures. The ALD deposition of iron oxide with well-controlled phase and tunable magnetism demonstrated in this work provides a promising opportunity for the fabrication of 3D nano-devices to be used in catalysis, spintronics, microelectronics, data storages and bio-applications.

Origin of the Reversible Thermochromic Properties of Polydiacetylenes Revealed by Ultrafast Spectroscopy

Polydiacetylenes (PDAs) with thermochromic properties undergo colorimetric transitions when the external temperature is varied. This capability has the potential to enable these materials to be used as temperature sensors. These thermochromic properties of PDAs stem from their temperature-dependent optical properties. In this work, we studied the temperature-dependent optical properties of Bis-PDA-Ph, which exhibits reversible thermochromic properties, and PCDA-PDA, which exhibits irreversible thermochromic properties, by UV-visible absorption and femtosecond transient absorption spectroscopy. Our results indicate that the electronic relaxation of PDAs occurs via an intermediate state in cases where the material exhibits reversible thermochromic properties, whereas the excited PDAs relax directly back to the ground state when irreversible thermochromic properties are observed. The existence of this intermediate state in the electronic relaxation of PDAs thus plays an important role in determining their thermochromic properties. These results are very important for both understanding and strategically modulating the thermochromic properties of PDAs.

A 3D networked polydiacetylene sensor for enhanced sensitivity

Immobilization of polydiacetylene (PDA) vesicles on the surface of the modified carbon nanotube (CNT)-networked pillared structures afforded a 3D networked sensor system. A more than three order increase in the sensitivity was observed with the 3D networked sensor matrix in comparison with a conventional 2D PDA sensor system.

Chromatic response of polydiacetylene vesicle induced by the permeation of methotrexate

The noble vesicular system of polydiacetylene showed a red shift using two types of detecting systems. One of the systems involves the absorption of target materials from the outer side of the vesicle, and the other system involves the permeation through the vesicular layers from within the vesicle. The chromatic mixed vesicles of N-(2-aminoethyl)pentacosa-10,12-diynamide (AEPCDA) and dimethyldioctadecylammonium chloride (DODAC) were fabricated by sonication, followed by polymerization by UV irradiation. The stability of monomeric vesicles was observed to increase with the polymerization of the vesicles. Methotrexate was used as a target material. The polymerized mixed vesicles having a blue color were exposed to a concentration gradient of methotrexate, and a red shift was observed indicating the adsorption of methotrexate on the polydiacetylene bilayer. In order to check the chromatic change by the permeation of methotrexate, we separated the vesicle portion, which contained methotrexate inside the vesicle, and checked chromatic change during the permeation of methotrexate through the vesicle. The red shift apparently indicates the disturbance in the bilayer induced by the permeation of methotrexate. The maximum contrast of color appeared at the equal molar ratio of AEPCDA and DODAC, indicating that the formation of flexible and deformable vesicular layers is important for red shift. Therefore, it is hypothesized that the system can be applicable for the chromatic detection of the permeation of methotrexate through the polydiacetylene layer.

Polydiacetylene-embedded microbeads for colorimetric and volumetric sensing of hydrocarbons

Rational design of a hydrocarbon sensor that enables visual differentiation of saturated aliphatic hydrocarbons (SAHCs) is very difficult owing to the lack of useful functional groups that can interact with the sensor system. Here, we report a microbead embedded with polydiacetylene that undergoes faster swelling and faster blue-to-red color change in response to the hydrocarbons of shorter alkyl chains. Accordingly, visual differentiation among n-pentane, n-heptane, n-nonane, and n-undecane was readily achieved. By taking advantage of the collective effect, construction of a sensor system with amplified response was possible. Combination of microfluidic technology (for bead preparation), PDMS (swellable polymeric matrix), and polydiacetylene (colorimetric material) was key to enabling this unique hydrocarbon sensor.

Preparation of CNC-dispersed Fe3O4 nanoparticles and their application in conductive paper

Well-dispersed Fe3O4 nanoparticles (NPs) were synthesized by a co-precipitation method in the presence of cellulose nano-crystals (CNC) as the template. The thus prepared Fe3O4 NPs were then used as a coating agent for the preparation of conductive paper. Fourier transform infrared spectroscopy (FTIR) results revealed that the Fe3O4 NPs were immobilized on the CNC through interactions between the hydroxyl groups of CNC and Fe3O4. Scanning transmission electron microscopy (STEM) images showed that the Fe3O4 NPs prepared in the presence of CNC can be dispersed in the CNC network, while the Fe3O4 NPs prepared in the absence of CNC tended to aggregate in aqueous solutions. The conductivity of the Fe3O4 NPs coated paper can reach to 0.0269 S/m at the coating amount of 14.75 g/m(2) Fe3O4/CNC nanocomposites. Therefore, the thus obtained coated paper can be potentially used as anti-static packaging material in the packaging field.

Electrochromic fiber-shaped supercapacitors

An electrochromic fiber-shaped super-capacitor is developed by winding aligned carbon nanotube/polyaniline composite sheets on an elastic fiber. The fiber-shaped supercapacitors demonstrate rapid and reversible chromatic transitions under different working states, which can be directly observed by the naked eye. They are also stretchable and flexible, and are woven into textiles to display designed signals in addition to storing energy.

Optical waveguide based on a polarized polydiacetylene microtube

An optical waveguide based on a PDA microtube has been prepared through a novel hierarchical assembly method. The waveguide performance of the PDA microtube can be easily modulated upon external stimuli. The polarization of the out-coupled emission light seems independent of the propagation distance, which should be ascribed to the ordered alignment of PDA chains in the microtube.

Encoding molecular information in plasmonic nanostructures for anti-counterfeiting applications

We present the next generation covert plasmonic security labels based on Ag nanowire structures and their polarization dependent surface-enhanced Raman scattering (SERS) imaging. The security labels consist of Ag nanowires fabricated by two-photon lithography and thermal evaporation, where molecular probes of choice are deposited. Simulation and experimental results show that the SERS signals from the embedded molecules depend significantly on the polarization of the incident field. The covert molecular information cannot be revealed directly from the physical features, but can only be read-out selectively by polarization-dependent SERS imaging. Our plasmonic security labels exhibit very narrow spectral fingerprint vibration, which is more specific than broadband colorimetry-based systems. The polarization-dependent SERS intensity, molecular fingerprint of SERS spectra, and versatile geometrical design by two-photon lithography have made our plasmonic Ag nanowire structures an ideal candidate as advanced security solutions for anti-counterfeiting application.

Unprecedented colorimetric responses of polydiacetylenes driven by plasma induced polymerization and their patterning applications

In this communication, we report that polydiacetylenes (PDAs) can be alternatively prepared via a plasma induced polymerization process.

Voltage-induced chromatic phase transition in ferrocene substituted polydiacetylene thin films

A novel ferrocene substituted PDA (FEPDA) material was synthesized and its chromatic phase transition behavior was studied under the application of a negative bias voltage. By the combination with CMS techniques, FEPDA materials could be used as a probe for mapping the topographic carrier density distribution in organic devices.

A soluble, low-temperature thermochromic and chemically reactive polydiacetylene

The majority of polydiacetylenes (PDAs) described to date display thermochromic transitions above room temperature. By following a strategy that employs headgroups that do not participate in strong interactions, we have designed and prepared a liquid diacetylene (DA) monomer that solidifies at a temperature near 0 °C. The isocyanate-containing DA monomer, DA-NCO, having this property does not undergo polymerization in its liquid state at room temperature. However, UV irradiation of frozen DA-NCO at 0 °C causes the instantaneous formation of a blue PDA (PDA-NCO). Interestingly, PDA-NCO was found to display a sharp blue-to-red color transition at a temperature near 11 °C. By taking advantage of its room temperature liquid-phase property, we were able to readily transfer the DA monomer to solid substrates by using common stamping and writing methods used for creating patterned PDA images. In addition, PDA-NCO dissolves in chloroform, giving a yellow solution that becomes red and simultaneously generates polymer aggregates when hexane is added. Finally, the isocyanate moieties present in PDA-NCO have been utilized to differentiate 1° from 2° and 3° amines owing to the fact that a chloroform solution of PDA-NCO undergoes a rapid yellow-to-red color change associated with an insoluble urea-forming reaction with primary amines.

Controlling and assessing the surface display of cell-binding domains on magnetite conjugated fluorescent liposomes

Biological systems provide us with a diverse source of peptide-based ligands for cellular adhesion. Controlling and assessing the ligand surface density as well as tailoring the surface chemistry to have specific cellular adhesion properties are important in biomaterials design. In the following work, we provide a means for displaying peptide-based ligands on magnetic liposomes in which the surface density and chemistry may be controlled. Simultaneously, the conjugated vesicles provide a fluorescent signal for examining steric hindrance among surface ligands. In addition, the inherent magnetic and fluorescence features of this system revealed potential for magnet-based cell isolation and fluorescent labeling of adhered cells, respectively. Adhered cells were found to remain viable and proliferative, thereby allowing them to be used for subsequent evaluation. In a specific demonstration, we control the density of fibronectin-mimetic ligands on the polydiacetylene liposome surfaces. We find that steric limitation occurring at over 20% surface density result in decreased cell adhesion, in accord with related techniques. The magnetic-liposome system offers the means for not only separating cells adhered to the biomaterial, but also providing the ability to control and assess the biomaterial surface. This may prove particularly useful for examining combinations of peptide-based ligands or for evaluating the molecular-level ligand accessibility and its effect on cell attachment to a biomaterial surface.

Inkjet-compatible single-component polydiacetylene precursors for thermochromic paper sensors

Inkjet-printable diacetylene (DA) supramolecules, which can be dispersed in water without using additional surfactants, have been developed. The supramolecules are generated from DA monomers that contain bisurea groups, which are capable of forming hydrogen-bonding networks, and hydrophilic oligoethylene oxide moieties. Because of suitable size distribution and stability characteristics, the single DA component ink can be readily transferred to paper substrates by utilizing a common office inkjet printer. UV irradiation of the DA-printed paper results in generation of blue-colored polydiacetylene (PDA) images, which show reversible thermochromic transitions in specific temperature ranges. Inkjet-printed PDAs, in the format of a two-dimensional (2D) quick response (QR) code on a real parking ticket, serve as a dual anticounterfeiting system that combines easy decoding of the QR code and colorimetric PDA reversibility for validating the authenticity of the tickets. This single-component ink system has great potential for use in paper-based devices, temperature sensors, and anticounterfeiting barcodes.

The alignment of carbon nanotubes: an effective route to extend their excellent properties to macroscopic scale

To improve the practical application of carbon nanotubes, it is critically important to extend their physical properties from the nanoscale to the macroscopic scale. Recently, chemists aligned continuous multiwalled carbon nanotube (MWCNT) sheets and fibers to produce materials with high mechanical strength and electrical conductivity. This provided an important clue to the use of MWCNTs at macroscopic scale. Researchers have made multiple efforts to optimize this aligned structure and improve the properties of MWCNT sheets and fibers. In this Account, we briefly highlight the new synthetic methods and promising applications of aligned MWCNTs for organic optoelectronic materials and devices. We describe several general methods to prepare both horizontally and perpendicularly aligned MWCNT/polymer composite films, through an easy solution or melting process. The composite films exhibit the combined properties of being flexible, transparent, and electrically conductive. These advances may pave the way to new flexible substrates for organic solar cells, sensing devices, and other related applications. Similarly, we discuss the synthesis of aligned MWCNT/polymer composite fibers with interesting mechanical and electrical properties. Through these methods, we can incorporate a wide variety of soluble or fusible polymers for such composite films and fibers. In addition, we can later introduce functional polymers with conjugated backbones or side chains to improve the properties of these composite materials. In particular, cooperative interactions between aligned MWCNTs and polymers can produce novel properties that do not occur individually. Common examples of this are two types of responsive polymers, photodeformable azobenzene-containing liquid crystalline polymer and chromatic polydiacetylene. Aligning the structure of MWCNTs induces the orientation of azobenzene-containing mesogens, and produces photodeformable polymer elastomers. This strategy also solves the long-standing problems from the traditional mechanical rubbing method, which include production of broken debris and structure damage during fabrication and building up electrostatic charge during use. Aligning MWCNTs induces a conformational change in polydiacetylene, which causes the composite fibers to be electrochromatic, a previously unknown reaction in chromatic polymers. Due to their large surface area, flexibility, electrical conductivity, and remarkable electrocatalytic activity, aligned MWCNT films can be used as counter electrodes to produce highly efficient dye-sensitized solar cells. In addition, chemists have developed new electrodes from the aligned MWCNT fibers to make a family of high-performing, wire-shaped dye-sensitized solar cells.

A protective layer approach to solvatochromic sensors

As they have been designed to undergo colorimetric changes that are dependent on the polarity of solvents, the majority of conventional solvatochromic molecule based sensor systems inevitably display broad overlaps in their absorption and emission bands. As a result, colorimetric differentiation of solvents of similar polarity has been extremely difficult. Here we present a tailor-made colorimetric and fluorescence turn-on type solvatochromic sensor that enables facile identification of a specific solvent. The sensor system displays a colorimetric transition only when a thin protective layer, which protects the solvatochromic materials, is destroyed or disrupted by a specific solvent. The versatility of the strategy is demonstrated by designing a sensor that differentiates chloroform and dichloromethane colorimetrically and one that performs sequence selective colorimetric sensing. In addition, the approach is employed to construct a solvatochromic molecular AND logic gate. The new strategy could open new avenues for the development of novel solvatochromic sensors.