Inkjet‐Printable Amphiphilic Polydiacetylene Precursor for Hydrochromic Imaging on Paper

Hydrochromic materials find great utility in a wide range of applications including humidity sensing and measuring the water contents of organic solvents, as well as substrates for rewritable paper and human sweat pore mapping. Herein, an inkjet printable diacetylene (DA) is described that can be transformed by UV irradiation to a hydrochromic‐conjugated polymer on conventional paper. Specifically, an amphiphilic DA that contains an ­imidazolium ion head‐group is found to be compatible with a common office inkjet printer. Various computer‐designed images are printed on paper using this substance. UV irradiation of the printed images results in the generation of blue‐colored images associated with formation of a polydiacetylene (PDA). The resolutions of the images are almost identical to those generated using a conventional black ink. Importantly, the printed images undergo a blue‐to‐red color change upon exposure to water and the hydrochromism is found to be temperature dependent. The facile color change that occurs near body ­temperatures enables use of the hydrochromic PDA‐coated paper for rapid and precise mapping of human sweat pores from fingers, palms, and feet.     

Mechanically Drawable Thermochromic and Mechanothermochromic Polydiacetylene Sensors

Recently, the development of directly writable techniques for depositing functional materials on solid substrates has received great attention. These pen‐on‐paper approaches enable generation of diverse patterned images on solid substrates in a flexible, easy handling, and inexpensive manner. Herein, the development of a directly writable conjugated polymer is described. Mechanically, drawable colorimetric polydiacetylene (PDA)–wax composites are readily fabricated by using a simple mixing‐molding method. Images are mechanically drawn on a paper substrate using the PDA–wax composites, display thermochromism, and mechanothermochromism. The thermochromic transition temperature is dependent on the melting point of the wax and, as a result, can be precisely controlled by the type of wax used. Optical microscopic analysis shows that formation of the DA–wax composite involves movement of wax molecules into a single diacetylene (DA) crystal. This process results in growth of the crystal. Importantly, the PDA crystal, obtained after UV light irradiation, undergoes significant shrinkage upon heating because of the release of monomers and the embedded wax molecules from the crystal. The release of these molecules creates void in the PDA supramolecules, allowing the PDA chains to undergo C–C bond rotation and hence the blue‐to‐red color transition.     

Inside Front Cover: Optical Control and Patterning of Gold‐Nanorod–Poly(vinyl alcohol) Nanocomposite Films (Adv. Funct. Mater. 7/2005)

The micropatterning of optical structures into thin films of poly (vinyl alcohol) (PVA) containing gold nanorods is demonstrated by Pérez‐Juste, Liz‐Marzán, and co‐workers on p. 1065. The nanorods are uniformly distributed in the thin films and can be aligned by stretching the films. The inside cover shows how irradiation with a nanosecond laser, using a TEM grid as mask, selectively reshapes the nanorods into nanospheres (upper and lower TEM images, respectively). Gold nanorods with well‐defined aspect ratios are homogeneously incorporated within poly(vinyl alcohol) thin films and subsequently aligned by heating and stretching the nanocomposite films. The spatial alignment of the nanorods is directly proved using transmission electron microscopy. The polarization‐dependent optical response of the rods is measured and compared with a dipole model. Excellent agreement is found. Additionally, irradiation of the film with nanosecond laser pulses (1064 nm) leads to selective reshaping of the nanorods into nanospheres, and we demonstrate that this effect can be used to micropattern optical structures into the films.     

Network Polydiacetylene Films: Preparation,Patterning, and Sensor Applications

The synthesis, characterization, and functionalization of polydiacetylene (PDA) networks on solid substrates is presented. A highly transparent and cross‐linked diacetylene film of DCDDA‐bis‐BA on a solid substrate is prepared first by tailoring the monomers with organoboronic acid moieties as pendant side groups and consequent drop‐casting and dehydration steps. Precisely controlled thermal curing plays a key role to obtain properly aligned diacetylene monomers that are closely packed between the boronic acid derived anhydride structures. A second cross‐linking, which occurs by polymerization of the diacetylene monomers with UV irradiation, induces a transparent to blue color shift. Accordingly, colored image patterns are readily available by polymerization through a photomask. The color change that takes place as a response to various organic solvents can be simply detected by naked eyes. The thermofluorescence change of PDA networks is demonstrated to be an effective method by which to obtain the microscale temperature distribution of thermal systems. The ease of film formation and stress‐induced blue‐to‐red color change with a simultaneous fluorescence generation features of the network structure should find a great utility in a wide range of chemical and thermal sensing platforms.     

Intercalation‐Induced Tunable Stimuli‐Responsive Color‐Change Properties of Crystalline Organic Layered Compound

Layered structures accommodate guest molecules and ions in the interlayer space through intercalation. Organic layered compounds, such as layered polymers, have both intercalation and dynamic properties. Here intercalation‐induced tunable temperature‐ and mechanical‐stress‐responsive color‐change properties of crystalline layered polydiacetylene (PDA) as an organic layered compound are reported. In general, organic materials with stimuli responsivity are developed by molecular design and synthesis. In the present work, intercalation of guest metal cations in the layered PDA directs tuning of the stimuli‐responsive color‐change properties, such as color, responsivity, and reversibility. Whereas PDA without intercalation of metal ions distinctly changes the color from blue to red at the threshold temperature, the PDA with intercalation of the divalent metal ions (PDA‐M²⁺) shows a variety of color‐change properties. The present study indicates that intercalation has versatile potentials for functionalization of organic layered compounds.     

A Printable Optical Time‐Temperature Integrator Based on Shape Memory in a Chiral Nematic Polymer Network

An optical and irreversible temperature sensor (e.g., a time‐temperature integrator) is reported based on a mechanically embossed chiral‐nematic polymer network. The polymer consists of a chemical and a physical (hydrogen‐bonded) network and has a reflection band in the visible wavelength range. The sensors are produced by mechanical embossing at elevated temperatures. A relative large compressive deformation (up to 10%) is obtained inducing a shift to shorter wavelength of the reflection band (>30 nm). After embossing, a temperature sensor is obtained that exhibits an irreversible optical response. A permanent color shift to longer wavelengths (red) is observed upon heating of the polymer material to temperatures above the glass transition temperature. It is illustrated that the observed permanent color shift is related to shape memory in the polymer material. The films can be printed on a foil, thus showing that these sensors are potentially interesting as time‐temperature integrators for applications in food and pharmaceutical products.     

White‐Emitting Conjugated Polymer/Inorganic Hybrid Spheres: Phenylethynyl and 2,6‐Bis(pyrazolyl)pyridine Copolymer Coordinated to Eu(tta)3

The synthesis of two cyan color (blue and green emission) displaying high molecular weight 2,6‐bis(pyrazolyl)pyridine‐co‐octylated phenylethynyl conjugated polymers (CPs) is presented. The conjugated polymers are solution‐processed to prepare spin coated thin films and self‐assembled nano/microscale spheres, exhibiting cyan color under UV. Additionally, the metal coordinating ability of the 2,6‐bis(pyrazolyl)pyridine available on the surface of the CP films and spheres is exploited to prepare red emitting Eu(III) metal ion containing conjugated polymer (MCCP) layer. The fabricated hybrid (CP/MCCP) films and spheres exhibit bright white‐light under UV exposure. The Commission Internationale de l'Eclairage (CIE) coordinates are found to be (x = 0.33, y = 0.37) for hybrid films and (x = 0.30, y = 0.35) for hybrid spheres. These values are almost close to the designated CIE coordinates for ideal white‐light color (x = 0.33, y = 0.33). This easy and efficient fabrication technique to generate white‐color displaying films and nano/microspheres signify an important method in bottom‐up nanotechnology of conjugated polymer based hybrid solid state assemblies.     

Tuning the Emitting Color of Organic Light‐Emitting Diodes Through Photochemically Induced Transformations: Towards Single‐Layer,Patterned, Full‐Color Displays and White‐Lighting Applications

Photochemically induced emission tuning for the definition of pixels emitting the three primary colors, red, green, blue (RGB), in a single conducting polymeric layer is investigated. The approach proposed is based on an acid‐induced emission shift of the (1‐[4‐(dimethylamino)phenyl]‐6‐phenylhexatriene) (DMA‐DPH) green emitter and acid‐induced quenching of the red fluorescent emitter (4‐dimethylamino‐4′‐nitrostilbene) (DANS). The two emitters are dispersed in the wide bandgap conducting polymer poly(9‐vinylcarbazole) (PVK), along with a photoacid generator (PAG). In the unexposed film areas, red emission is observed because of efficient energy transfer from PVK and DMA‐DPH to DANS. Exposure of selected areas of the film at different doses results in quenching of the red emitter's fluorescence and the formation of green, blue, or even other color‐emitting pixels, depending on the exposure dose and the relative concentrations of the different compounds in the film. Organic light‐emitting diodes having the PVK polymer containing the appropriate amounts of DMA‐DPH, DANS, and PAG as the emitting layer are fabricated and electroluminescence spectra are recorded. The time stability of induced emission spectrum changes and the color stability during device operation are also examined, and the first encouraging results are obtained.     

A Colorimetric Hydrocarbon Sensor Employing a Swelling‐Induced Mechanochromic Polydiacetylene

Exceptional challenges have confronted the rational design of colorimetric sensors for saturated aliphatic hydrocarbons (SAHCs). The main reasons for this difficulty are the extremely nonpolar nature of these targets and their lack of functional groups that can interact with probes. By taking advantage of a mechanochromic conjugated polydiacetylene (PDA) and the hydrocarbon‐induced swelling properties of polydimethylsiloxane (PDMS), a sensor film that enables simple, colorimetric differentiation between a variety of C5 to C14 aliphatic hydrocarbons is fabricated. The unprecedented PDA–PDMS composite sensor undergoes a blue‐to‐red colorimetric transition on a timescale that is dependent on the chain length of the hydrocarbon target. In addition, the development of the red color is directly proportional to the swelling ratio of the film. This straightforward approach enables naked‐eye differentiation between n‐pentane and n‐heptane. The versatility of the sensor system is demonstrated by using it for the colorimetric determination of kerosene in adulterated diesel oil. Finally, the observation that a PDA microcrystal in the film undergoes significant expansion and tearing in concert with a blue‐to‐red colorimetric transition during the swelling process provides direct evidence for the mechanism for the mechanochromic behavior of the PDA.     

Inkjet Printing of Luminescent CdTe Nanocrystal–Polymer Composites

Inkjet printing is used to produce well‐defined patterns of dots (with diameters of ca. 120 μm) that are composed of luminescent CdTe nanocrystals (NCs) embedded within a poly(vinylalcohol) (PVA) matrix. Addition of ethylene glycol (1–2 vol %) to the aqueous solution of CdTe NCs suppresses the well‐known ring‐formation effect in inkjet printing leading to exceptionally uniform dots. Atomic force microscopy characterization reveals that in the CdTe NC films the particle–particle interaction could be prevented using inert PVA as a matrix. Combinatorial libraries of CdTe NC–PVA composites with variable NC sizes and polymer/NC ratios are prepared using inkjet printing. These libraries are subsequently characterized using a UV/fluorescence plate reader to determine their luminescent properties. Energy transfer from green‐light‐emitting to red‐light‐emitting CdTe NCs in the composite containing green‐ (2.6 nm diameter) and red‐emitting (3.5 nm diameter) NCs are demonstrated.     

Universal Colorimetric Detection of Nucleic Acids Based on Polydiacetylene (PDA) Liposomes

A universal colorimetric method for the detection of nucleic acids, based on ionic interactions by polydiacetylene (PDA) liposomes, is described. Primary and quaternary amine‐modified diacetylene monomers were synthesized and used to generate positively charged PDA liposomes. The resulting PDA sensors showed a dramatic color change from blue to red upon the addition of nucleic acids amplified by using the polymerase chain reaction (PCR) due to the stimuli caused by ionic interactions between the positively charged PDA and negatively charged phosphate backbone of the nucleic acids. The color change that takes place can be simply detected by the naked eye. Compared with quaternary amine‐functionalized PDA vesicles, the primary amine‐functionalized PDA underwent a more intense color transition under optimized conditions. By using the PDA‐based colorimetric sensor, nucleic acids amplified by common PCR reaction, whose typical concentration is around 100 nM, can be readily detected. Since implementation of this universal colorimetric method is simple, rapid and does not require any sophisticated instrumentation, it should have greatly enhanced applications as a technology for DNA diagnosis.     

Assembly of Layered Rare‐Earth Hydroxide Nanosheets and SiO2 Nanoparticles to Fabricate Multifunctional Transparent Films Capable of Combinatorial Color Generation

Colloidal solutions of layered rare‐earth hydroxide nanosheets provide a simple route to deposit ultra thin luminescence films. The antireflection and antifogging properties were integrated into transparent luminescent films by the layer‐by‐layer assembly of Eu³⁺, Tb³⁺, Dy³⁺ doped‐hydroxocation nanosheets and negatively‐charged SiO₂ nanoparticles. Resulting multifunctional films exhibited efficient red, green, and blue emissions with controllable intensity. Highly improved transmittance enabled us to display combinatorial color luminescence, which can be achieved by multiply overlapping individual films with different combinations, without significant loss of transparency. Triple overlap of red/green/blue films generated an excellent white‐light under 254 nm UV irradiation.     

Novel Chromogenic Esters of ortho‐Phenylazonaphthols

We have prepared the photo‐labile benzoic acid esters and the acid‐labile tert‐butoxycarbonyl esters of Sudan I and Sudan Red B, two representatives of the ortho‐phenylazonaphthol dye family, exhibiting hydroxyazo–hydrazone tautomerism with the hydrazone as the strongly favored form. The chromophores obtained are “locked” in an exclusive azo configuration and exhibit absorbance spectra which are dramatically blue‐shifted (more than 100 nm) and have strongly reduced extinction coefficients when compared to their parent chromophores. Thus, the esters of the orange dye Sudan I exhibit an absorption maximum in the ultraviolet (UV) regime, and the esters of the red dye Sudan Red B appear yellow. Depending on the nature of the ester moiety, by irradiation with UV light or by exposure to preferentially photochemically released acidic species at elevated temperatures, these esters can be reverted to the parent, highly tinctured Sudan I and Sudan Red B, respectively. Unlike conventional chromogenic systems, these dyes are compatible with melt‐processible polymers and do not require any wet‐chemical development. In polymer films comprised of these chromogenic dyes, color patterns can be produced directly by masked irradiation. We here report on the synthesis, spectral properties, and conversion kinetics of these novel chromogenic dyes, which may be potentially suitable for marking and labeling goods in a lithographic process and for optical data storage and sensing applications.     

A Combinatorial Approach for Colorimetric Differentiation of Organic Solvents Based on Conjugated Polymer‐Embedded Electrospun Fibers

A combinatorial approach for the colorimetric differentiation of organic solvents is developed. A polydiacetylene (PDA)‐embedded electrospun fiber mat, prepared with aminobutyric acid‐derived diacetylene monomer PCDA‐ABA 1, displays colorimetric stability when exposed to common organic solvents. In contrast, a fiber mat prepared with the aniline‐derived diacetylene PCDA‐AN 2 undergoes a solvent‐sensitive color transition. Arrays of PDA‐embedded microfibers are constructed by electrospinning poly(ethylene oxide) solutions containing various ratios of two diacetylene monomers. Unique color patterns are developed when the conjugated polymer‐embedded electrospun fiber arrays are exposed to common organic solvents in a manner which enables direct colorimetric differentiation of the tested solvents.     

Carbazole–Dibenzofuran Dyads as Metal‐Free Single‐Component White‐Color Photoemitters

White‐color light emitters from single organic molecule without heavy metals are valuable for practical applications in organic light‐emitting devices. In this study, carbazole (Cz)–dibenzofuran (DBF) donor–acceptor dyads are designed for white‐color light emitters. Originally, these molecules show photoluminescence (PL) in near ultraviolet region. However, upon successive ultraviolet (UV) irradiation, white‐color PL appears, comprising dual‐color phosphorescence from the amorphous and crystalline state of the dyad. A continuous UV irradiation makes the twisting angle between the Cz and DBF planes flatten through the triplet‐excited state, which proceeds crystallization. Thermal annealing and UV irradiation can switch the blue‐ and white‐color phosphorescences from the dyad. Furthermore, charge injection generates white‐color electroluminescence. The materials with PL color modulation ability by UV‐light irradiation and heating can be applicable as light‐ and thermo‐sensors.     

Heterogeneous Transparent Ultrathin Films with Tunable‐Color Luminescence Based on the Assembly of Photoactive Organic Molecules and Layered Double Hydroxides

Multicolor luminescent films have great potential for use in optoelectronics, solid‐state light‐emitting materials, and optical devices. This work describes a systematic investigation of the ordered assembly of two‐ (blue/green, blue/orange, red/blue, red/green) and three‐color (blue/red/green) light‐emitting ultrathin films (UTFs) by using different photofunctional anions [bis(N‐methylacridinium)@polyvinylsulfonate ion pairs and anionic derivatives of poly(p‐phenylene), poly(phenylenevinylene), and poly(thiophene)] and Mg‐Al‐layered double hydroxide nanosheets as building blocks. The rational combination of luminescent components affords precise control of the emission wavelengths and intensity, and multicolored luminescent UTFs can be precisely tailored covering most of the visible spectral region. The assembly process of the UTFs and their luminescence properties, as monitored by UV–vis absorption and fluorescence spectroscopy, resulted in a gradual change in luminescence color in the selected light‐emitting spectral region upon increasing the number of deposition cycles. X‐ray diffraction demonstrates that the UTFs are periodic layered structures involving heterogeneous superlattices associated with individual photoactive anion–LDH units. These UTFs also exhibit well‐defined multicolor polarized fluorescence with high polarization anisotropy, and the emissive color changes with polarization direction. Therefore, this work provides a way of fabricating heterogeneous UTFs with tunable‐color luminescence as well as polarized multicolor emission, which have potential applications in the areas of light displays and optoelectronic devices.     

Ultrathin Polydopamine Films with Phospholipid Nanodiscs Containing a Glycophorin A Domain

Cellular membranes have long served as an inspiration for nanomaterial research. The preparation of ultrathin polydopamine (PDA) films with integrated protein pores containing phospholipids and an embedded domain of a membrane protein glycophorin A as simplified cell membrane mimics is reported. Large area, ultrathin PDA films are obtained by electropolymerization on gold surfaces with 10–18 nm thickness and dimensions of up to 2.5 cm². The films are transferred from gold to various other substrates such as nylon mesh, silicon, or substrates containing holes in the micrometer range, and they remain intact even after transfer. The novel transfer technique gives access to freestanding PDA films that remain stable even at the air interfaces with elastic moduli of ≈6–12 GPa, which are higher than any other PDA films reported before. As the PDA film thickness is within the range of cellular membranes, monodisperse protein nanopores, so‐called “nanodiscs,” are integrated as functional entities. These nanodisc‐containing PDA films can serve as semi‐permeable films, in which the embedded pores control material transport. In the future, these simplified cell membrane mimics may offer structural investigations of the embedded membrane proteins to receive an improved understanding of protein‐mediated transport processes in cellular membranes.     

A Novel Neutral State Green Polymeric Electrochromic with Superior n‐ and p‐Doping Processes: Closer to Red‐Blue‐Green (RGB) Display Realization

Two donor‐acceptor systems, 4,7‐di‐2‐thienyl‐2,1,3‐benzoselenadiazole (TSeT) and 4,7‐di‐2,3‐dihydrothieno[3,4‐b][1,4]dioxin‐5‐yl‐2,1,3‐benzoselenadiazole (ESeE) are synthesized and electropolymerized to give polymers PTSeT and PESeE, respectively. One of the polymers, PTSeT, is blue‐green in the neutral state and soluble, exhibiting a deep‐red emission color. The other, PESeE, is the first 2,1,3‐benzoselenadiazole‐based neutral state green polymer with a narrow bandgap (1.04 eV). Furthermore, PESeE has superior and durable n‐ and p‐doping processes. Beyond the stability and the robustness, both of the polymer films exhibit multi‐electrochromic behavior.     

A New Anti‐Counterfeiting Feature Relying on Invisible Luminescent Full Color Images Printed with Lanthanide‐Based Inks

Europium and terbium trisdipicolinate complexes are inkjet printed onto paper with commercially available desktop inkjet printers. Together with a commercial blue luminescent ink, the red‐emitting luminescent ink containing europium and the green‐emitting luminescent ink containing terbium are used to reproduce accurate full color images that are invisible under white light and appear under a 254 nm UV light. Such invisible luminescent images are attractive anti‐counterfeiting security features. The luminescent prints have a color range (gamut) nearly as wide as the gamut of a standard sRGB display. The gamut of the luminescent prints is determined by relying on a simple model predicting the relative spectral radiant emittances of any printed luminescent color halftone. The model is also used to establish the correspondence between the surface coverages of the printed luminescent inks and the emitted color of these luminescent halftones. The accuracy of the spectral prediction model is very good and can be rationalized by the absence of quenching when the luminescent lanthanide complexes are printed in superposition with the other luminescent materials.     

Photochemical Formation of Au/Cu Bimetallic Nanoparticles with Different Shapes and Sizes in a Poly(vinyl alcohol) Film

Metal nanoparticle (NP)–polymer nanocomposite thin films are attractive for applications in various devices. Since bimetallic NPs provide additional opportunities for tuning the physical properties of the NP components, the development of bimetallic NP nanocomposite thin films should lead to further enhancements of various applications. Au/Cu bimetallic NPs are fabricated in a poly(vinyl alcohol) (PVA) film using a photochemical process. Interestingly, different sizes and shapes of Au/Cu bimetallic NPs are formed in the PVA film, resulting in a uniquely patterned nanocomposite structure. It is determined that the different formation and growth mechanisms of NPs inside and outside the UV‐light irradiation spot leads to the differences in size and shape.