Tuning of Thermochromic Properties of Polydiacetylene toward Universal Temperature Sensing Materials through Amido Hydrogen Bonding

A Color-Detectable Vitamin C Controlled-Release System Fabricated Using Electrospinning

This study develops a vitamin C controlled-release system, trackable via color changes as a function of vitamin C release. The system is composed of coaxial microfibers prepared via coaxial electrospinning, with a core of poly(ethylene oxide) (PEO) incorporating vitamin C, and a shell composed of polycaprolactone (PCL) containing polydiacetylene (PDA) as the color-changing material. The shell thickness is controlled by adjusting the amount of PCL ejected during electrospinning, allowing regulation of the release rate of vitamin C. When vitamin C added to PEO penetrates the PCL layer, the color of PDA changes from blue to red, indicating a color change. The results of this study can be applied to devices that require immediate detection of vitamin C release levels.

Effect of UV Irradiation Time and Headgroup Interactions on the Reversible Colorimetric pH Response of Polydiacetylene Assemblies

Polydiacetylenes are chromatic conjugated polymers formed upon the photopolymerization of self-assembled diacetylenes. They exhibit conformation-dependent colorimetric responses, usually irreversible, to external triggers. Here, we presented an approach to obtain a reversible colorimetric response to a pH change through structural modifications on the monomer and extended photopolymerization time. Both factors, enhanced hydrogen bond forming headgroups and longer UV exposure, impacted the rotational freedom of polydiacetylene conformation. Such a restricted conformation state reduced colorimetric response efficiency but enabled reversible colorimetric response to a pH change. These results highlight the possibility of obtaining a reversible colorimetric pH response of polydiacetylenes for customized sensing applications through monomer-level tailoring combined with tuning the photopolymerization time.

Dual Nanofriction Force Microscopy/Fluorescence Microscopy Imaging Reveals the Enhanced Force Sensitivity of Polydiacetylene by pH and NaCl

Polydiacetylene (PDA) is a popular mechanochromic material often used in biosensing. The effect of its headgroup-headgroup interactions on thermochromism such as pH or salt concentration dependency has been extensively studied before; however, their effect on mechanochromism at the nanoscale is left unstudied. In this work, nanofriction force microscopy and fluorescence microscopy were combined to study the effect of pH and ionic strength on the polydiacetylene (PDA) force sensitivity at the nanoscale. We found that the increase in pH from 5.7 to 8.2 caused an 8-fold enhancement in force sensitivity. The elevation of NaCl concentration from 10 to 200 mM also made the PDA 5 times more force-sensitive. These results suggest that the PDA force sensitivity at the nanoscale can be conveniently enhanced by "pre-stimulation" with pH or ionic strength.

Structures and strategies for enhanced sensitivity of polydiacetylene(PDA) based biosensor platforms

Polydiacetylene (PDA) is a versatile polymer that has been studied in numerous fields because of its unique optical properties derived from alternating multiple bonds in the polymer backbone. The conjugated structure in the polymer backbone enables PDA to possess the ability of blue-red colorimetric transition when π-π interactions in the PDA backbone chain are disturbed by the external environment. The chromatic property of PDA disturbed by external stimuli can also emit fluorescence in the red region. Owing to the unique characteristics of PDA, it has been widely studied in facile and label-free sensing applications based on colorimetric or fluorescence signals for several decades. Among the various PDA structures, membrane structures assembled by amphiphilic molecules are widely used as a versatile platform because facile modification of the synthetic membrane provides extensive applications, such as receptor-ligand interactions, resulting in potent biosensors. To use PDA as a sensory material, several methods have been studied to endow the specificity to PDA molecules and to amplify the signal from PDA supramolecules. This is because selective and sensitive detection of target materials is required at an appropriate level corresponding to each material for applicable sensor applications. This review focuses on factors that affect the sensitivity of PDA composites and several strategies to enhance the sensitivity of the PDA sensor to various structures. Owing to these strategies, the PDA sensor system has achieved a higher level of sensitivity and selectivity, enabling it to detect multiple target materials for a full field of application.

Alkali Metal Salts of 10,12-Pentacosadiynoic Acid and Their Dosimetry Applications

Wide-dose-range 2D radiochromic films for radiotherapy, such as GAFchromic EBT, are based on the lithium salt of 10,12-pentacosadiynoic acid (Li-PCDA) as the photosensitive component. We show that there are two solid forms of Li-PCDA-a monohydrated form A and an anhydrous form B. The form used in commercial GAFchromic films is form A due to its short needle-shaped crystals, which provide favorable coating properties. Form B provides an enhanced photoresponse compared to that of form A, but adopts a long needle crystal morphology, which is difficult to process. The two forms were characterized by powder X-ray diffraction, Fourier transform infrared spectroscopy, CP-MAS ¹³C solid-state NMR spectroscopy, and thermogravimetric analysis. In sum, these data suggest a chelating bridging bidentate coordination mode for the lithium ions. The sodium salt of PCDA (Na-PCDA) is also reported, which is an ionic cocrystal with a formula of Na⁺PCDA^-·3PCDA. The PCDA and PCDA^- ligands display monodentate and bridging bidentate coordination to the sodium ion in contrast to the coordination sphere of the Li-PCDA forms. In contrast to its lithium analogues, Na-PCDA is photostable.

Polydiacetylene and its composites with long effective conjugation lengths and tunable third-order nonlinear optical absorption

Through the deliberate annealing of suspensions, bluish-green phase polydiacetylene and polydiacetylene composites that have remarkably extended ECLs were effectively fabricated that exhibit different nonlinear optical absorption types.

Covalent Cross-Linking of Diketopyrrolopyrrole-Based Organogels with Polydiacetylenes

A new strategy toward functional materials with novel properties and well-defined structures has been developed through the topochemical polymerization of diacetylene-containing diketopyrrolopyrrole (DPP) derivatives. In order to enable the efficient photopolymerization and cross-linking of the materials, a rational design of DPP-based derivatives has been performed to incorporate amide moieties, thus enabling the formation of intermolecular hydrogen bonds and the formation of an organogel. The new materials showed good gelation properties in aromatic solvents, resulting in the formation of a dense fibrous network in the gel state. Upon UV irradiation, the supramolecular self-assemblies obtained were shown to be efficiently cross-linked through the conversion of diacetylene into polydiacetylene. A detailed investigation of new resulting materials was performed by a combination of morphological characterization tools, including X-ray diffraction, Raman spectroscopy, and atomic force microscopy. Our results demonstrate that the topochemical polymerization of diacetylene-containing DPP-based compounds is a promising strategy toward new electroactive and well-defined materials, without the use of catalysts or additives, thus creating new opportunities for the preparation and processing of π-conjugated materials.

Utilization of chromic polydiacetylene assemblies as a platform to probe specific binding between drug and RNA

Recognition of nucleic acids remains an important endeavor in biology. Nucleic acids adopt shapes ranging from A-form (RNA and GC rich DNA) to B-form (AT rich DNA). We show, in this contribution, shape-specific recognition of A-U rich RNA duplex by a neomycin (Neo)-polydiacetylene (PDA) complex. PDA assemblies are fabricated by using a well-known diacetylene (DA) monomer, 10,12-pentacosadiynoic acid (PCDA). The response of poly(PCDA) assemblies is generated by mixing with a modified neomycin-PCDA monomer (Neo-PCDA). The functionalization by neomycin moiety provides specific binding with homopolyribonucleotide poly (rA) - poly (rU) stimulus. Various types of alcohols are utilized as additives to enhance the sensitivity of poly(PCDA)/Neo-PCDA assemblies. A change of absorption spectra is clearly observed when a relatively low concentration of poly (rA)-poly (rU) is added into the system. Furthermore, poly(PCDA)/Neo-PCDA shows a clear specificity for poly (rA)-poly (rU) over the corresponding DNA duplex. The variation of linker between neomycin moiety and conjugated PDA backbone is found to significantly affect its sensitivity. We also investigate other parameters including the concentration of Neo-PCDA and the DA monomer structure. Our results provide here preliminary data for an alternative approach to improve the sensitivity of PDA utilized in biosensing and diagnostic applications.

Thermoluminescent microparticle thermal history sensors

While there are innumerable devices that measure temperature, the nonvolatile measurement of thermal history is far more difficult, particularly for sensors embedded in extreme environments such as fires and explosions. In this review, an extensive analysis is given of one such technology: thermoluminescent microparticles. These are transparent dielectrics with a large distribution of trap states that can store charge carriers over very long periods of time. In their simplest form, the population of these traps is dictated by an Arrhenius expression, which is highly dependent on temperature. A particle with filled traps that is exposed to high temperatures over a short period of time will preferentially lose carriers in shallow traps. This depopulation leaves a signature on the particle luminescence, which can be used to determine the temperature and time of the thermal event. Particles are prepared-many months in advance of a test, if desired-by exposure to deep ultraviolet, X-ray, beta, or gamma radiation, which fills the traps with charge carriers. Luminescence can be extracted from one or more particles regardless of whether or not they are embedded in debris or other inert materials. Testing and analysis of the method is demonstrated using laboratory experiments with microheaters and high energy explosives in the field. It is shown that the thermoluminescent materials LiF:Mg,Ti, MgB₄O₇:Dy,Li, and CaSO₄:Ce,Tb, among others, provide accurate measurements of temperature in the 200 to 500 °C range in a variety of high-explosive environments.

Reversible Chromatic Response of Polydiacetylene Derivative Vesicles in D2O Solvent

The thermal chromatic sensitivity of polydiacetylenes (PDAs) with 10,12-pentacosadiynoic acid (PCDA) derivatives, which have a hydroxyl group (HEEPCDA) and an amine group (APPCDA), were investigated using D2O and H2O as solvents. The vesicle solution with polymerized HEEPCDA exhibited a reversible chromatic response during the heating and cooling cycle in D2O, but not in H2O. On the other hand, the vesicle solution with the polymerized APPCDA exhibited a reversible chromatic response in H2O during the heating and cooling cycle, but the color of the solution did not change much in D2O. The critical vesicle concentration of HEEPCDA was lower in D2O than in H2O, and the chromatic sensitivity of the polymerized vesicles to temperature was slower in D2O than in H2O. We think that it is due to D2O being a more highly structured solvent than H2O with the hydrogen bonding in D2O stronger than that in H2O.

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.

Topochemical polymerization of unsymmetrical aryldiacetylene supramolecules with nitrophenyl substituents utilizing C-H∙∙∙π interactions

Diacetylenes are versatile building blocks, in which many functional groups can be incorporated for the construction of new materials with desirable properties. In this study, 6-(p or m-nitrophenyl)-3,5-hexadiyne-1-ol (4a or 4b) containing nitrophenyl groups (host) and 2-hydroxyethyl groups (guest) in different diacetylene terminals were designed to establish an ordered supramolecular assembly that is complied with the strict requirements for the topochemical polymerization of diacetylenes. Crystal film and bulk crystals of compound 4b were obtained successfully by cast film and re-precipitation methods. Both of these could photopolymerize to the corresponding regular poly(diacetylene) polymer, as evidenced by UV-vis, IR, FL and Raman spectroscopy. The electrochemical properties and behaviors of 4a and 4b were also investigated, and the results show that the differences between the para and meta positions of the mono-phenylacetylene substituents probably result from the topochemical polymerization. Thus, m-nitrophenylbutadiyne derivatives with sizeable C-H∙∙∙π interactions seemed to be effective for the formation of a polymerizable packing, which is appropriate for topochemical polymerization.

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.

Poly(methyl methacrylate)-supported polydiacetylene films: unique chromatic transitions and molecular sensing

Polydiacetylenes (PDAs) constitute a family of conjugated polymers exhibiting unique colorimetric and fluorescence transitions, and have attracted significant interest as chemo- and biosensing materials. We spin-coated PDA films upon poly(methyl methacrylate) (PMMA), and investigated the photophysical properties and sensing applications of the new PDA configuration. Specifically, the as-polymerized blue PDA layer underwent distinct transformations to purple, red, and yellow phases, which could be quantified through conventional color scanning combined with application of image analysis algorithms. Furthermore, we recorded a reversible red-purple PDA transition that was induced by ultraviolet irradiation, a phenomenon that had not been reported previously in PDA film systems. We show that distinct color and fluorescence transitions were induced in the PMMA-supported PDA films by amphiphilic substances-surfactants and ionic liquids-and that the chromatic transformations were correlated to the analyte structures and properties. Overall, this study presents a new chromatic PDA film system in which noncovalent interactions between the PMMA substrate and spin-coated PDA give rise to distinct chromatic properties and molecular sensing capabilities.

Multifunctional polydiacetylene-liposome with controlled release and fluorescence tracing

A multifunctional polydiacetylene-liposome (PDA-liposome) was prepared by self-assembly, which can be characterized with controlled drug release and fluorescence tracing.

Dye sublimation as a measure of accumulated heat exposure

Heat history monitor: Combination of the sublimation and adsorption processes of specific dyes can be used as a measure of accumulated heat exposure. Mass transfer from the sublimation layer to the adsorption layer strongly depends on temperature and results in a gradual color change in the adsorption layer. The total color change reflects the accumulated heat exposure.

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.