Reversible Thermochromism Research Articles

A urea-modified polydiacetylene-based high temperature reversible thermochromic sensor: Characterisation and evaluation of properties as a function of temperature

Modification of polydiacetylene (PDA) with a small compound capable of forming multiple hydrogen bonds resulted in new and improved qualities such as high-temperature reversible thermochromism and higher melting temperature. Several distinct colours were exhibited to indicate different temperatures. Polydiacetylenes often suffer from irreversible thermochromic transitions and that limits their applicability in sensor development. A simple thermochromic PDA sensor that exhibits reversible thermochromism up to 150°C is reported. This was achieved by introducing urea to the head group of 10,12-pentacosadiynoic acid (PCDA) and shining 254nm UV light to the resulting fine powders to form a deep-blue-coloured poly-pcd-urea. Thermochromic and thermal properties of the PDA were investigated using ultraviolet–visible (UV–vis) and X-ray diffraction (XRD) spectroscopic techniques; and thermogravimetric (TG) and differential scanning calorimetry (DSC) analyses. UV–vis studies revealed that poly-pcd-urea returned to its original blue colour when it was heated up to 150°C. DSC and XRD revealed that the reason for loss of reversibility was probably because poly-pcd-urea melted at 151°C and upon solidifying did not fully recover the crystalline structure responsible for its blue colour. TG analysis showed that the polymer was thermally stable up to 315°C.

Visual Detection of pH and Biomolecular Interactions at Micromolar Concentrations Aided by a Trivalent Diacetylene-Based Vesicle

A trivalent tris-(alkylenediynoic acid) is developed as a new monomer to prepare a poly(tris-(diacetylene)). Alkylenediynoic moieties, covalently linked to the gallic acid, lead to a high propensity for polymerization, resulting in blue poly(tris-(diacetylene)), within less than 20 s of UV irradiation as aq. vesicle solution and as thin film. The vesicle undergoes reversible thermochromism between room temperature and 95 °C. The corresponding chromism changes are blue-to-red-to-orange during heating and reverse on cooling. This reversible chromism also occurs to thin film between room temperature and 220 °C. The polymerized aq. vesicle exhibits pH-induced chromism in the alkaline range. In order to identify polymerization-induced chromatic transitions beneficial to a biosensing process, derivatization of the monomer with α-d-mannopyranoside moieties is conducted. Chromatic properties of sugar-derivatized tris-(alkylenediynoic acid) vesicle are established first. Poly(tris-(diacetylene)) vesicles, prepared from either pure or mixed monomer systems, exhibit blue phase, which do not undergo change in chromism when the sugar–lectin interaction is initiated. Whereas, when the monomer vesicle is prepared in the presence of the lectin and polymerized subsequently, chromism of the resulting poly(tris-(diacetylene)) solution is pink, as a result of ligand–lectin interaction. The chromism change can be conducted at ≈10 × 10−6 m each of both vesicle and the lectin.

New Dendritic Polydiacetylene Sensor with Good Reversible Thermochromic Ability in Aqueous Solution and Solid Film.

Thermal responsive polydiacetylene derived from PAMAM dendrimer (PDA-G0) was synthesized. Unlike the ethylenediamine substituted PDA (PDA-NH2) solution, the prepared PDA-G0 vesicle solution showed reversible thermochromism property when temperature varied from 20 to 90 °C, which is due to the formation of an internal hydrogen bond in amide groups. Furthermore, PDA-G0/PMMA film with excellent stability was obtained by a mixed-drying method, which could be stored for a long time without denaturation. After polymerization by UV irradiation, it displayed much better reversible thermochromic ability and the responded temperature range became wider, from 20 to 110 °C.

Fluorescent Molecular Rotors of Organoboron Compounds from Schiff Bases: Synthesis, Viscosity, Reversible Thermochromism, Cytotoxicity, and Bioimaging Cells.

We report the design, synthesis, and characterization of two new fluorescent molecular rotors of boron derived from Schiff bases: (2,4,8,10-tetra-tert-butyl-6-phenyldibenzo[d,h][1,3,6,2]dioxazaboronine (3) and 1,4-bis(2,4,8,10-tetra-tert-butyldibenzo[d,h][1,3,6,2]dioxazaboronin-6-yl)benzene (4), as well as the free ligand 2-[[(3,5-di-tert-butyl-2-hydroxyphenyl)imino]methyl]-4,6-di-tert-butylphenol 1. All compounds were fully characterized by NMR (1H, 11B, and 13C), IR, UV/vis, fluorescence spectroscopy, and high-resolution mass spectrometry. The crystal structures of 3 and 4 showed tetracoordinated boron atoms with semiplanar skeleton ligands. The free rotation of the fluorescent molecular rotor, only observed in the binuclear compound, was decreased with increasing viscosity, while the quantum yield was increased. Interestingly, the property of reversible thermochromism was found in organoboron 4 in the solid state. DFT calculations to determine the both complexes have free rotation around the CPh-B1 bond. The boron compounds 3 and 4 have shown low cytotoxicity activity in cell line A-431 and low green staining in cells.

Dynamic Thermal Mechanical Behaviors and Mechanical Properties of Reversible Thermochromism Wood-Plastic Composite

To prepare a late-model and functional wood-plastic composite (WPC), the reversible thermochromism crystal violet lactone microcapsule was prepared by situ polymerization, then fabricated reversible thermochromism WPC by microcapsule and low density polyethylene with Maleic anhydride grafted polyethylene. Comparing the L, a and b data of apparent color of reversible thermochromism WPC, the value of chromatism (ΔE) showed the difference of heating before and after, it was also measured to characterize the color-change level; the mechanical properties of ordinary WPC and reversible thermochromism WPC were measured respectively to compare the advantages and disadvantages of two kinds of WPC; Then the storage modulus and loss modulus of ordinary WPC and reversible thermochromism WPC were determined to distinguish the good from the bad of two kinds of composites. The results indicated that the reversible thermochromism WPC is a functional composite with noticeable color-changed effects, and tensile strength, bending strength and interface compatibility were better than ordinary WPC, but had worse impact property contrarily.

Reversibly thermochromic bismuth-organic materials with tunable optical gaps

Reversible thermochromism in color tunable bismuth-organic hybrid materials.

Reversible solid-state thermochromism of a 2D organic–inorganic hybrid perovskite structure based on iodoplumbate and 2-aminomethyl-pyridine

An organic–inorganic hybrid solid [(PyCH2NH3)6][Pb5I22]·3H2O with a 2D inorganic layer exhibited a reversible color change from orange to red at 80 °C in the solid state.

Role of Zn2 + ion on the formation of reversible thermochromic polydiacetylene/zinc oxide nanocomposites

Polydiacetylene (PDA)/zinc oxide (ZnO) nanocomposite is a class of materials that exhibit reversible thermochromism with controllable color-transition temperature. The nanocomposite also changes color upon exposure to various types of acids and bases. In our continuing efforts to develop this material, we obtain evidences that reveal true nature of the nanocomposite formation. X-ray diffraction (XRD) technique detects a significant increase of the interlamellar distance within the nanocomposite comparing to that of the pure constituent PDA. The investigation of the nanocomposite systems prepared from 10,12-tricosadiynoic acid and 10,12-pentacosadiynoic acid provides consistent results. This indicates an intercalation of the Zn2+ ions, leaking out of the ZnO nanoparticles, between the PDA layers. An atomic absorption spectroscopy confirms the existence of Zn2+ ions in the aqueous solution. The XRD result also shows that using only Zn2+ ions to prepare the nanocomposite can provide the intercalated PDA/Zn2+ structure. However, the enhanced inter- and intrachain interactions within this system is not sufficient to provide reversible thermochromism. An infrared spectroscopy detects the variation of vibrational frequencies of carboxylate head groups within the systems of PDA/ZnO nanocomposite and PDA/Zn2+ assemblies, corresponding to different types of interactions. Therefore, the strong interfacial interaction between PDA head groups and ZnO nanoparticle is essential for obtaining the reversible thermochromism. We also attempt to prepare the nanocomposites by using a combination of Zn2+ ions and various types of substrates including TiO2, SiO2 and Al2O3 nanoparticles.

Preparation of thermochromic polymer nanocomposite films from polymerizable organogels of oligothiophene-based organogelators

Thermochromic polymer nanocomposite films were prepared from polymerizable organogels. Organogelator 1 had a structure which 3,4,5-tris(ω-decenyl)benzamide groups were attached to a quarterthiophene core through amide bonds. Organogelator 2 had the same structure except that tris(ω-decenyl) groups were replaced by tris(n-decanyl) groups. The PMMA nanocomposite films were prepared by the photopolymerization of the organogels formed in methyl methacrylate (MMA). The film containing 1 (0.5 wt%) showed reversible thermochromism. The emission under 365 nm irradiation was changed to bright green from orange by heating up to 120 °C and returned to its initial orange by cooling. To the contrary, the PMMA composite film prepared from the organogel of 2 (0.5 wt%) did not show a reversible thermochromic property. Organogelator 1 with polymerizable terminal vinyl groups was covalently embedded in the PMMA matrix, but 2 was not. The reversible thermochromism was likely caused by the thermally reversible conformational change of quarterthiophene units in the polymer fibers.

Structural-thermochromic relationship of polydiacetylene (PDA)/polyvinylpyrrolidone (PVP) nanocomposites: Effects of PDA side chain length and PVP molecular weight

Abstract Reversible thermochromic polydiacetylene (PDA)/polyvinylpyrrolidone (PVP) nanocomposites are prepared by using 6 diacetylene (DA) monomers. The use of relatively low molecular weight (MW) PVP provides the nanocomposites with reversible thermochromism. The shortening of PDA alkyl tail causes the decrease of color-transition temperature, ranging from 75 to 85 °C. The shortening of alkyl segment adjacent to PDA carboxylic head group, however, does not provide the same trend. The nanocomposites constituting PDAs with 8, 6 and 4 methylene units exhibits color-transition at about the same temperature. The increase of PVP MW reduces the color-transition temperature and also affects thermochromic reversibilty of the PDA/PVP nanocomposites.

Chromotropism in halo-bridged dimers. Structural characterization of bis(μ-halo)bis(halo N-(pyridin-2-ylmethyl)cyclohexanamine copper(II))

Two dinuclear copper(II) complexes, [LCu(μ-Cl)Cl]2 (DMF) (1) and [LCu(μ-Br)Br]2 (2), with the bidentate ligand N-(pyridin-2-ylmethyl)cyclohexanamine, L, were synthesized and characterized by physicochemical and spectroscopic (IR, UV–vis) data. The crystal structural analysis of 1 shows that both copper(II) ions are in a distorted square pyramidal N2Cl3 environment with the apical position of the copper(II) being occupied by the bridging chloride anion which is equatorial to the other copper ion, forming a dimeric copper(II) complex. The chromotropic properties of both complexes, including solvato-, thermo-, and halochromism, were investigated. The complexes show reversible thermochromism in solution which is irreversible in the solid state. It was found that the solvatochromism is due to structural change followed by solvation of the vacant sites of the complexes. Their halochromic properties were studied in pH range of 1–11 by visible absorption spectroscopy. The color changes from blue to green and to colorless are due to deprotonation and protonation of the ligands.

Reversible thermochromism via hydrogen-bonded cocrystals of polydiacetylene and melamine

Abstract In this study, we report a unique two-step approach to prepare pure and well-organized 10,12-pentacosadiynoic acid (DA)/melamine (MA) cocrystals, from which the topochemically polymerized product, poly(10,12-pentacosadiynoic acid) (PDA)/MA cocrystals, demonstrated reversible thermochromism (note that PDA in its pure crystalline form is thermochromically irreversible). In the first step, co-assembling DA and MA was achieve in a selective solvent for MA (i.e., water) using the non-covalently connected micelle method. In the second step, annealing the DA/MA co-assembly at a temperature higher than the melting point of pure DA crystals (62 °C) but below that of the cocrystals (87 °C) led to the formation of pure DA/MA cocrystals with a molar ratio of 2:1. The resultant lath-like DA/MA cocrystals were nano-sized and had an alternating DA/MA lamellar structure. Due to the strong intermolecular hydrogen-bonding and π-π stacking of MA molecules, the topochemically polymerized PDA/MA cocrystals were completely reversible in thermochromism. This is the first example that reversible thermochromism of PDA is realized through hydrogen-bonding assisted cocrystals with a small molecule.

Versatile route to prepare reversible thermochromic polydiacetylene nanocomposite using low molecular weight poly(vinylpyrrolidone)

Abstract This contribution introduces a simple method to prepare polydiacetylene(PDA)-based materials with reversible thermochromism. The incorporation of low molecular weight poly(vinylpyrrolidone) (PVP10) into the PDA assemblies, prepared from 10,12-pentacosadiynoic acid (PCDA) monomer, enhances inter- and intrachain interactions within the system. The PVP10 is simply added during conventional preparation methods without requiring any other treatments. X-ray diffraction technique reveals the increase of interlamellar distance, which indicates the intercalation of PVP10 chains with the poly(PCDA) layers. The resultant poly(PCDA)/PVP10 nanocomposite exhibits higher color-transition temperature compared to that of the pure poly(PCDA) assemblies. In addition, the blue-to-purple color transition of poly(PCDA)/PVP10 nanocomposite in aqueous solution is fully reversible during 10 consecutive heating/cooling cycles. When the poly(PCDA)/PVP10 nanocomposite is fabricated into thin film, it exhibits two-steps color transition, reversible blue-to-purple at 90 °C and reversible purple-to-red at 150 °C. The complete color reversibility of this system persists up to 200 °C. Raman scattering spectroscopy is utilized to investigate color stability and the change of PDA backbone conformation within the nanocomposite during the color-transition process. We also demonstrate that the preparation conditions such as the PVP10 concentration and incubation time significantly affect the color reversibility of the resultant nanocomposites. Their size and shape are influenced by the PCDA/PVP10 mixing process.

Structure and chromotropism properties of an unsymmetrical alkoxo-bridged nickel(II) cubane-like complex

A new tetranuclear cubane-like complex, [Ni4(L)4Cl4(H2O)3(EtOH)]·(H2O), has been synthesized from the reaction of a metal salt with the bidentate ligand 2-hydroxymethylpyridine (LH), and its crystal structure, spectroscopic and chromotropic properties have been studied. The complex has a [Ni4O4] core comprising a distorted cubane arrangement, of which four nickel(II) ions were bridged by μ3-alkoxo moieties. Each nickel(II) was coordinated to three μ3-alkoxo oxygens, one pyridine nitrogen and one chloride. The peripheral ligation was completed by an oxygen atom of water or ethanol ligand, which participated in intramolecular hydrogen bonding. Chromotropism properties of the complex including solvato-, thermo-, and ionochromism were investigated. The complex displayed strong ionochromism and shows high-sensitive and selective activity toward CN− and SCN− anions in the presence of other halides and pseudo-halides. The solvatochromic property of the complex was analyzed by a multi-parametric equation using SPSS/PC software. The stepwise multiple linear regression method demonstrated that the acceptor power of the solvent plays the most important role in the observed negative solvatochromism of the compound. It shows reversible thermochromism in solution due to loss of the weakly coordinated water and ethanol from the nickel(II) units.

In Situ Encapsulation of Ultrasmall CuO Quantum Dots with Controlled Band-Gap and Reversible Thermochromism.

Silica encapsulated ultrasmall CuO quantum dots (QDs; CuO@SiO2) were synthesized by reverse microemulsion. The CuO QDs with sizes ranging from 2.0 to 1.0 nm with corresponding band gaps of 1.4 to 2.6 eV were prepared simply by varying the concentration of the Cu(2+) precursor. The samples were characterized by Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and UV-vis spectroscopy. The CuO@SiO2 composite displayed reversible thermochromism which resulted from the strong electron-phonon coupling of ultrasmall CuO in the confined space of SiO2 and the enhanced band-gap shift in the visible light region depending on temperature. Besides, the as synthesized CuO@SiO2 was found to be highly stable for reversible thermochromism due to the micropore structure of silica matrix and local confinement of the QDs.

Symmetrically Related Construction and Optical Properties of Two Noncentrosymmetric 3D Iodides of d(10) Cation (Cu(+), Ag(+)) Based on the N-Benzylpyridinium and Its Supramolecular Interactions.

Two noncentrosymmetric compounds, namely, [N-Bz-Py]2[Cu6I8] (1) and [N-Bz-Py]4[Ag9I13] (2) (N-Bz-Py(+) = N-benzylpyridinium), with three-dimensional open frameworks, were synthesized solvothermally via in situ benzylation of pyridine. 1 is constructed from 3-connected Cu3I7 secondary building units (SBUs) with chiral (10,3)-a topology, while the occluded N-Bz-Py(+) forms a complementary supramolecular (10,3)-a net via π-π interactions. 2 is characteristic of acentric connections of trimeric Ag3I8 and hexamer Ag6I12 SBU, while N-Bz-Py(+) in the channels aggregates into asymmetrically supramolecular chains via π-π interactions. Remarkable structural correlations imply the unique amplification and transfer of asymmetric information from V-shaped N-Bz-Py(+) to organic supramolecular nets and inorganic frameworks, which are confirmed by their second harmonic generation responses. Adsorption spectra reveal their semiconductive nature (2.52 eV for 1 and 3.02 eV for 2) and interesting reversible thermochromism for 1 based on the intermolecular charge transfer.

Geometry flexibility of copper iodide clusters: variability in luminescence thermochromism.

An original copper(I) iodide cluster of novel geometry obtained by using a diphosphine ligand is reported and is formulated [Cu6I6(PPh2(CH2)3PPh2)3] (1). Interestingly, this sort of "eared cubane" cluster based on the [Cu6I6] inorganic core can be viewed as a combination of the two known [Cu4I4] units, namely, the cubane and the open-chair isomeric geometries. The synthesis, structural and photophysical characterisations, as well as theoretical study of this copper iodide along with the derived cubane (3) and open-chair (2) [Cu4I4(PPh3)4] forms, were investigated. A new polymorph of the cubane [Cu4I4(PPh3)4] cluster is indeed presented (3). The structural differences of the clusters were analyzed by solid-state nuclear magnetic resonance spectroscopy. Luminescence properties of the three clusters were studied in detail as a function of the temperature showing reversible luminescence thermochromism for 1 with an intense orange emission at room temperature. This behavior presents different feature compared to the cubane cluster and completely contrasts with the open isomer, which is almost nonemissive at room temperature. Indeed, the thermochromism of 1 differs by a concomitant increase of the two emission bands by lowering the temperature, in contrast to an equilibrium phenomenon for 3. The luminescence properties of 2 are very different by exhibiting only one single band when cooled. To rationalize the different optical properties observed, density functional theory calculations were performed for the three clusters giving straightforward explanation for the different luminescence thermochromism observed, which is attributed to different contributions of the ligands to the molecular orbitals. Comparison of 3 with its [Cu4I4(PPh3)4] cubane polymorphs highlights the sensibility of the emission properties to the cuprophilic interactions.

A thermochromic silver nanocluster exhibiting dual emission character.

A Ag12(SCH2C10H7)6(CF3CO2)6(CH3CN)6 (1) nanocluster modified using naphthalen-2-yl-methanethiol was synthesized and structurally characterized by single crystal X-ray analysis. The targeted luminescent nanocluster displays dual emission with the property of reversible thermochromism spanning from red to bright yellow.

High color stability and reversible thermochromism of polydiacetylene/zinc oxide nanocomposite in various organic solvents and polymer matrices

Abstract Polydiacetylene (PDA)-based materials exhibit color transition when subjected to external stimuli, making them attractive for sensing technology. The utilization of PDA-based materials can be largely extended by fabricating in different polymer matrices, which normally involves organic solvents as media. Recently, our group has developed PDA/zinc oxide (ZnO) nanocomposites, exhibiting reversible thermochromism in aqueous medium. In this contribution, we demonstrate that the PDA/ZnO nanocomposite can be dispersed in various organic solvents including 1,2-dichlorobenzene, chlorobenzene, toluene, ethanol, butanol, hexanol, chloroform and tetrahydrofuran. The color of pure PDA changes from blue to red in these solvents while the PDA/ZnO nanocomposite remains blue after 30 days. The color reversibility and color-transition temperature of the PDA/ZnO nanocomposite are hardly affected in these organic solvents compared to the system of aqueous medium. We further demonstrate that the PDA/ZnO nanocomposite can be embedded in common polymer matrices such as poly(styrene), poly(methyl methacrylate), poly(ethylene) and poly(vinyl alcohol) by using a simple mixing process. We have found that color reversibility of the PDA/ZnO nanocomposite depends on property of the polymer matrices and persists up to about 200 °C in some systems. The ability to prepare PDA-based materials in different organic solvents and polymer matrices is very important for their utilization in various applications.

Research and Application of Retention Agent in Reversible Thermochromism Materials Papermaking

This paper discusses the effects of different retention agent such as: CPAM, APAM, PAE+CPAM, cationic starch with high degree of substitution and modified starch on the reversible thermochromism materials in anti-counterfeiting paper retention rate, and then determined the optimum dosage of retention agent in the slurry. According to the anti-counterfeit paper color value, the mechanism of reversible thermochromism paper was studied. The experimental results show that when the slurry with retention agent, the reversible thermochromism materials in the anti-counterfeit paper retention increased significantly. This suggests that retention agent in pulp fiber has played the role of bridge and link, thus ensuring the security of reversible thermochromism paper.