Spectroscopic studies of polydiacetylene solutions and glasses

Absorption, fluorescence excitation and emission spectra of a soluble polydiacetylene, obtained by the solid-state polymerization of the bis-(phenyl acetate) ester of 10,12-docosadiyne-1. 22-diol, have been recorded at room and liquid-nitrogen temperatures for different solvents. Spectral shifts, similar to those reported for other soluble polydiacetylenes, are observed on addition of a non-solvent or on cooling the solutions. The fluorescence quantum yield was measured from 2-methyl tetrahydrofuran solution at room temperature. The yield, was roughly one hundred times larger for this system at 77 K and well-structured fluorescence spectra were observed for this low-temperature glass.     

Effect of amphiphilic molecules upon chromatic transitions of polydiacetylene vesicles in aqueous solutions

Effect of amphiphilic molecules upon the chromatic transitions of polymerized 10,12-pentacosadiynoic acid (PCDA) vesicles in aqueous solutions was reported. The colorimetric response of polymerized PCDA vesicles for 1-pentanol is higher than that for ethanol due to more hydrophobic property of 1-pentanol. The colorimetric response of polymerized PCDA vesicles for sodium dodecyl sulfate (SDS) and Triton X-100 is lower than that for cetyltrimethylammonium bromide (CTAB). The strong ability of CTAB to induce chromatic transition of the vesicles is related to the positively charged headgroups of CTAB, which favors approach of CTAB to the negatively charged carboxylate groups at the vesicle surface. The insertion of alkyl chain of CTAB into the hydrophobic domain perturbs the conformation of the conjugated polymer backbone and induces color change of polydiacetylene vesicles. For a series of alkylamine hydrochloric salts, the longer the alkyl chain, the stronger the ability of alkylamine to induce chromatic transition of polydiacetylene vesicles.     

Thermochromism and Solvatochromism in Solution

Summary.  The thermochromic behaviour of various coordination compounds in solution is discussed, with a special focus on cyclic diamine chelates. Thermally induced spin-crossover phenomena of iron(II) complexes are also considered. The solvatochromic behaviour of mixed-ligand complexes is presented in detail. Received April 2, 2001. Accepted (revised) April 19, 2001     

Thermochromism and Solvatochromism in Solution

 The thermochromic behaviour of various coordination compounds in solution is discussed, with a special focus on cyclic diamine chelates. Thermally induced spin-crossover phenomena of iron(II) complexes are also considered. The solvatochromic behaviour of mixed-ligand complexes is presented in detail.     

Thermochromism of polypropylene gels

It is found that polypropylene gels in some solvents of benzene-derivatives show a striking change of colour. The colour changes from blue to yellow as the temperature rises from the melting point of the solvent to around 70–80 °C. The apparent characteristic of the phenomenon resembles the thermochromism of cholesteric liquid crystals although polypropylene itself is colourless and has no asymmetric carbons in the molecules. Polypropylene flakes swelled in these solvents also show similar thermochromism.     

光(热)致变色现象

在光照或加热的情况下,某些物质的颜色会发生可逆性的变化,称之为光（热）致变色现象。此类物质的种类不同,其变色机理不同,所呈现的颜色也不同。此现象首先发现于无机物,并已有130余年的历史。但不论是在合成与理论研究上,还是在实际应用上的迅速发展,却是在近30余年来更显得卓有成效。光（热）致变色物质目前已在图像显示、光记录材料、彩色录像、照像、印刷照排、化妆品、染料、装饰品、油漆、玩具、护目镜等方面得到了不同程度的应用。     

Thermochromism of perylenes: dynamics in aromatics

A thermal equilibrium between planar and skew perylene derivatives induces thermochromism and may modulate molecular recognition. Thus, the long-lasting discussion about the geometry of perylene could be solved in terms of this equilibrium. Extension to other aromatics and practical applications such as for non contact fluorescence thermometers are discussed.     

Excitonic quadrupole absorption in a polydiacetylene

Excitonic states in a polydiacetylene (polyTCDU) single crystal have been investigated using temperature-dependent optical absorption, Raman and polarization-dependent optical spectroscopy. The expected significance of a linear quadrupolar component in the excitonic transition has been experimentally demonstrated. Formation and detectability of such quadrupoles is a unique attribute of the symmetry, order, valence geometry and one-dimensionality of the polydiacetylene backbone.     

High-modulus polydiacetylene single-crystal fibers

The relationship between structure and mechanical properties of polydiactetylene single-crystal fibers has been studied in detail. It is shown by transmission electron microscopy that the fibers have a high degree of internal perfection, with the polymer molecules aligned parallel to the fiber axes. The fibers of the dicarbazolyl derivative investigated were found to have a Young's modulus of 45 GPa and fracture strengths of up to 1.5 GPa, the strengths being controlled by defects such as surface steps. It is shown that the stiffness of the polymer backbone is similar to that of polyethylene, and the theoretical strength of the polydiacetylene singlecrystal fibers is determined to be about 3 GPa, corresponding to a fracture strain of between 6 and 8% and a force required to break molecules to the order of 3 nN. The derivative studied is also found to have good thermal stability, not degrading below 300°C, and excellent creep resistance up to at least 100°C. The possibility of using the single-crystal fibers in composites is also discussed.     

Controlling Thermochromism in a Photonic Block Copolymer Gel

The tunable properties of stimulus‐responsive materials attract great interest in a variety of technological applications. Photonic gels are a new class of these materials, which can be tuned to reflect different wavelengths of light. Controlling this reflected color via temperature‐induced changes of self‐assembled photonic materials is important for their application in sensors and displays. In this work, the thermochromic behavior of a PS–P2VP photonic gel was found to originate from a temperature‐induced change in the pK_a of the P2VP blocks. Control was obtained through the manipulation of the solution pH. The findings of this work provide the basis for understanding and controlling the properties of thermochromic block copolymers fostering their use in technologically relevant applications.     

Thermochromism of poly-1-butene gels

Poly-1-butene gels in some solvents of benzene-derivatives show a colouring phenomenon. The colour changes from blue to yellow under irradiation of natural light as the temperature rises from the melting point of the solvent to the sol-gel transition temperature. The colouring phenomenon is due to selective scattering, but not to optical absorption. The apparent characteristics of the phenomenon resemble the thermochromism of cholesteric liquid crystals, although poly-1-butene itself is colourless and has no asymmetric carbons.     

Elementary excitations in linear-chain conjugated polydiacetylene molecules

Absorption, emission and excitation spectra of matrix-isolated fully conjugated polydiacetylene molecules are presented. The interpretation of the spectral features in terms of excitons, polarons and electron-hole pairs is based on recent theoretical concepts.     

Thermochromism of bacteriorhodopsin and its pH dependence

Purple membranes (PMs), which consist of the photochromic membrane protein bacteriorhodopsin (BR) and lipids only, show complex thermochromic properties. Three different types of reversible temperature-dependent spectral transitions were found, involving spectral states absorbing at 460, 519, and 630 nm. These thermochromic absorption changes were analyzed in the range from 10 to 80 degrees C. In dependence on the bulk pH value, hypsochromic or bathochromic shifts in the BR absorption spectra are observed in BR gels as well as in BR films. The thermochromic changes between both purple and blue or purple and red were quantified in the CIE color system. The molecular changes causing these effects are discussed, and a model is presented in terms of intramolecular protonation equilibriums. The thermochromic properties of BR may be of interest in applications like security tags, as this feature may complement the well-known photochromic properties of BR.     

Electronic structures of polydiacetylene backbones

Energies per unit cell for various polydiacetylene backbone sequences are determined. The unrestricted Hartree-Fock approach is used to obtain the lowest energy transitions.     

Theory of the rod-to-coil transition in polydiacetylene

A theory is proposed for the rod to coil transition in polydiacetylene 4BCMU and related polymers which is based on the hypothesis that the high-temperature (yellow) phase consists predominantly of the cis structure, while the low-temperature (red) phase is trans. Because the occurrence of a cis-trans interface is energetically costly, the correlation length for either isomer remains long and the transition is sharp, much like the helix-coil transition in the theory of Zimm and Bragg. The transition is driven by the higher entropy of the cis isomer, which is free to coil, unlike the trans or butatriene forms. The theory gives excellent agreement with optical absorption measurements and is consistent with all other experimental data for this system.     

Fluorescence resonance energy transfer in polydiacetylene liposomes

Conjugated polydiacetylene (PDA) possessing stimuli-responsive properties has been intensively investigated for developing efficient sensors. We report here fluorescence resonance energy transfer (FRET) in liposomes synthesized using different molar ratios of dansyl-tagged diacetylene and diacetylene-carboxylic acid monomers. Photopolymerization of diacetylene resulted in cross-linked PDA liposomes. We used steady-state electronic absorption, emission, and fluorescence anisotropy (FA) analysis to characterize the thermal-induced FRET between dansyl fluorophores (donor) and PDA (acceptor). We found that the monomer ratio of acceptor to donor ( R ad) and length of linkers (functional part that connects dansyl fluorophores to the diacetylene group in the monomer) strongly affected FRET. For R ad = 10 000, the acceptor emission intensity was amplified by more than 18 times when the liposome solution was heated from 298 to 338 K. A decrease in R ad resulted in diminished acceptor emission amplification. This was primarily attributed to lower FRET efficiency between donors and acceptors and a higher background signal. We also found that the FRET amplification of PDA emissions after heating the solution was much higher when dansyl was linked to diacetylene through longer and flexible linkers than through shorter linkers. We attributed this to insertion of dansyl in the bilayer of the liposomes, which led to an increased dansyl quantum yield and a higher interaction of multiple acceptors with limited available donors. This was not the case for shorter and more rigid linkers where PDA amplification was much smaller. The present studies aim at enhancing our understanding of FRET between fluorophores and PDA-based conjugated liposomes. Furthermore, receptor tagged onto PDA liposomes can interact with ligands present on proteins, enzymes, and cells, which will produce emission sensing signal. Therefore, using the present approach, there exist opportunities for designing FRET-based highly sensitive and selective chemical and biochemical sensors.     

One-dimensional order/disorder in a polydiacetylene

A polydiacetylene film, found to be amorphous by x-ray diffraction, possesses some kind of order as suggested by differential scanning calorimetry (DSC). The order/disorder phenomenon which occurs upon heatingcooling is also accompanied by a green/yellow color transition. On the basis of analogies between crystallization and the order in this material, we have extended the application of the Avrami equation to determine the dimensionality of the order in the polymer. Kinetic analysis of the exothermic transition (disorder → order) by DSC suggests that the material has one-dimensional order. The disruption and formation of this order, which accompany the color changes in this polydiacetylene, give rise to endothermic and exothermic transitions, respectively. Supporting evidence for the proposed one-dimensional order/disorder concept is cited.     

Reversible Thermochromism and Strong Ferromagnetism in Two-Dimensional Hybrid Perovskites

Two-dimensional (2D) hybrid perovskites have shown many attractive properties associated with their soft lattices and multiple quantum well structure. Herein, we report the synthesis and characterization of two new multifunctional 2D hybrid perovskites, (PED)CuCl₄ and (BED)₂CuCl₆, which show reversible thermochromic behavior, dramatic temperature-dependent conductivity change, and strong ferromagnetism. Upon temperature change, the (PED)CuCl₄ and (BED)₂CuCl₆ crystals exhibit a reversible color change between yellow and red-brown. The associated structural changes were monitored by in situ temperature-dependent powder X-ray diffraction (PXRD). The (BED)₂CuCl₆ exhibits superior thermal stability, with a thermochromic working temperature up to 443 K. The conductivity of (BED)₂CuCl₆ changes over six orders of magnitude upon temperature change. The 2D perovskites exhibit ferromagnetic properties with Curie temperatures around 13 K.     

Effect of alkyl chain length on chemical sensing of polydiacetylene and polydiacetylene/ZnO nanocomposites

Polydiacetylenes (PDAs) and PDA/ZnO nanocomposites based on the monomers 10,12-pentacosadiynoic acid (PCDA), 10,12-tricosadiynoic acid (TCDA), and 10,12-docosadiynedioic acid (DCDA) monomers have been investigated for chromatic chemical sensing of a number of organic liquids. Chromatic sensitivity is associated with the interaction of the organic liquid with the PDA side chain to give rise to the strain-induced blue to red colorimetric transition. Attenuated total reflection (ATR) Fourier transform infrared (FTIR) spectroscopy demonstrated that in the PDA/ZnO nanocomposites, the PDA side chains form chelates with ZnO. The chromatic properties of PDAs and PDA/ZnO composites in organic liquids, to certain extent, depend on the side-chain length and the number of carboxylic head groups. Pure PDAs and PDA/ZnO nanocomposites in different organic liquids studied by Raman spectroscopy show that the chromatic selectivity of PDAs for certain organic liquids with respect to the blue to red phase transition is closely related to the side-chain structure of the PDAs. Moreover, the interactions are stronger with those PDAs where the blue to red transition is irreversible. Density functional theory (DFT) simulations show that the chromatic sensitivity of the PDAs toward a particular organic correlates with the C–C bond torsion angle of the PDA backbone.