Thermochromic Behavior Research Articles

Template-free synthesis of hollow yolk shelled VO2(M) microspheres and their application in effective removal of methylene blue

VO 2 (M) has attracted more and more attention due to the unique phase transition phenomenon. However, few discussions are focused on the adsorption performances of VO 2 (M) except for thermochromic behaviors. In this work, hollow yolk-shelled VO 2 (M) (VO 2 (M)-HYS) microspheres were synthesized by a template-free hydrothermal method. During this process, citric acid is both of the reducing agent and the directing agent. The reaction time and concentration of the precursor played key roles in the formation of VO 2 (M)-HYS. Under the optimum conditions, for the VO 2 (M)-HYS-4, the average size of microspheres was approximately 3.29 μm in diameter, the thickness of the shell was about 0.32 μm and the phase transition temperature was close to 59 °C. According to the adsorption results, VO 2 (M)-HYS-4 exhibited an excellent adsorption performance for methyl blue with a maximum adsorption capacity of 755.46 mg/g, which preferably satisfied the second-order kinetic adsorption model. Therefore, these porous VO 2 (M) microspheres with thermochromic behaviors may be extended to the fields of adsorption and photocatalysis.

Multiple stimulus responsive Co-AIE framework materials with reversible solvatochromic and thermochromic behaviors: molecular design, synthesis and characterization

A novel Co-AIE-MOF (Co-tcbpe) based on TPE derivatives is designed and synthesized. And it shows a multi-stimuli response in the application of reversible solvatochromism and thermochromism.

A healable, recyclable and thermochromic epoxy resin for thermally responsive smart windows

An epoxy resin modified by coordination between Ni2+and imidazole/hydroxyl groups show high mechanical strength and thermal healing/recycling/reprocessing/thermochromic behavior, and might be useful in the field of thermally-responsive smart windows.

Thermochromic and opacity behaviors in vanadium dioxide nanofilms: a theoretical study

Vanadium dioxide nanofilms are one of the most essential materials in electronic applications like smart windows. Therefore, studying and understanding the optical properties of such films is crucial to modify the parameters that control these properties. To this end, this work focuses on investigating the opacity as a function of the energy directed at the nanofilms with different thicknesses (1–100) nm. Effective mediator theories (EMTs), which are considered as the application of Bruggeman’s formalism and the Looyenga mixing rule, have been used to estimate the dielectric constant of VO2 nanofilms. The results show different opacity behaviors at different wavelength ranges (ultraviolet, visible, and infrared). The results depict that the highest opacity of the insulating phase is achieved at the ultraviolet region and it reduces for the metal phase. Besides, the results demonstrate that the opacity possesses a redshift during the changes at the three phases. Regarding the infrared region, the lowest opacity value is achieved at the insulator phase and it increases to the highest value at the metal phase. In the visible region, the opacity behavior remains similar in the three phases. It is worth noting that the lowest opacity is found for thinner nanofilm. Since both the refractive index and the extinction index are among the most essential optical constants, hence, both of them were compared with the experiment results, and an excellent agreement is achieved between them.

Transition metal complexes of the PPO/POP ligand: variable coordination chemistry and photo-luminescence properties.

In the current work the tautomeric equilibrium between tetraphenyldiphosphoxane (Ph2P-O-PPh2, POP) and tetraphenyldiphosphine monoxide (Ph2P-P(O)Ph2, PPO) in the absence and presence of transition metal precursors is investigated. Whereas with hard transition metal ions, such as Fe(II) and Y(III), PPO-type complexes, such as [FeCl2(PPO)2] (1) and [YCl3(THF)2(PPO)] (2), are formed, softer transition metals ions tend to form so-called coordination stabilised tautomers of the POP ligand form, such as [Cu2(MeCN)3(μ2-POP)2](PF6)2 (3), [Au2Cl2(μ2-POP)] (4), and [Au2(μ2-POP)2](OTf)2 (5). The photo-optical properties of the PPO- and POP-type transition metal complexes are investigated experimentally using photo-luminescence spectroscopy, whereby the presence of metallophillic interactions was found to play a crucial role. The dinuclear copper complex [Cu2(MeCN)3(μ2-POP)2](PF6)2 (3) shows a very interesting thermochromic behavior and intense photo-luminescence with remarkable phosphoresence lifetimes at 77 K, which can probably be attributed to short intramolecular Cu-Cu distances.

Mixed-halide copper-based perovskite R2Cu(Cl/Br)4 with different organic cations for reversible thermochromism

Mechanically exfoliated flakes of mixed-halide Cu-based perovskite crystals, R2Cu(Cl/Br)4, with three alkyl chains exhibit reversible thermochromic behavior with differences in crystal lattice behavior depending on the organic spacer used.

Tracking the optical constants of porous vanadium dioxide thin films during metal–insulator transition: Influence of processing conditions on their application in smart glasses

Vanadium dioxide (VO2) is widely recognized as a thermochromic material with great potential for application in smart glazing for energy-efficient buildings. The monoclinic (M1) VO2 phase undergoes a first-order reversible phase transition from the semiconductor to the rutile metallic state. In this study, an M1 VO2 porous film was synthesized via a polymer-assisted sol-gel route. Processing parameters, such as drying and reduction temperatures, were varied to evaluate their influence on the thermochromic behavior of VO2 and to determine the necessary trade-off between a significant thermochromic effect and high luminous transmittance. Film–silica glass–film systems with luminous transmittance close to 80% and IR solar modulation ability as large as 20% were prepared. By tracking the optical constants of the films during the thermochromic process, the changes produced at the microscopic level in the material could be correlated with its macroscopic behavior when used as an energy-saving material.

Crystal structure and thermochromic behavior of the quasi-0D lead-free organic-inorganic hybrid compounds (C7H9NF)8M4I16 (M = Bi, Sb)

The quasi 0D lead-free thermochromic organic-inorganic hybrid single crystals (C7H9NF)8M4I16 (M = Bi, Sb) were synthesized by a conventional solvothermal reaction method. The crystal structures were analyzed using single crystal X-ray diffraction (SXRD). Interestingly, as the temperature increases, the (C7H9NF)8M4I16 (M = Bi, Sb) crystals exhibit a peculiar thermochromic phenomenon. In order to explore the phenomenon of thermochromism, temperature dependent ultraviolet−visible-near-infrared (UV–vis–NIR) absorption spectra were measured. The bandgaps of (C7H9NF)8Sb4I16 and (C7H9NF)8Bi4I16 at room temperature are 2.34 eV and 2.1 eV, respectively, and they gradually decrease as the temperature increases. Combined with ab initio molecular dynamics (AIMD), the reduction of the bandgap at higher temperature and the occurrence of thermochromism could be caused by the stronger electronic activity (thermal excitation). The thermochromic characteristics of these low-dimensional organic-inorganic hybrid metal halides will provide alternative materials for smart windows temperature sensors, visual thermometers, and daylight control glasses and beyond.

Strong, transparent, and thermochromic composite hydrogel from wood derived highly mesoporous cellulose network and PNIPAM

Composite polymer hydrogels are of significant interests for high optical transparency and mechanical performance. In this work, a strong and transparent composite hydrogel is developed from a highly mesoporous cellulose network prepared from wood via top-down delignification followed by TEMPO-mediated oxidation and in situ polymerization of PNIPAM. Individualization of cellulose microfibrils inside the wood cell wall is critical for the fabrication of free-standing composite hydrogel with high water content of 94.9 wt% and high optical transmittance of 85.8% with anisotropic light scattering behavior. The composite hydrogel also showed anisotropic mechanical properties with a tensile strength, Young’s modulus and toughness of 317 kPa, 5.4 MPa, and 39.2 kJ m−3 in axial direction, and 152 kPa, 0.31 MPa and 57.1 kJ m−3 in the transverse direction, respectively. It also showed thermochromic behavior, i.e., reversibly changing between transparent and brightly white by a temperature change between 25 and 40 °C, demonstrating great potential for optical applications.

Perylene Bisimide-Based Luminescent Liquid Crystals with Tunable Solid-State Light Emission.

Perylene bisimides are among the most studied building blocks for supramolecular assemblies in the fabrication of optoelectronic devices for their exceptional optical and electronic properties; however, developing perylene bisimide-based luminescent liquid crystals remains a challenge for the strong π-stacking tendency of the large planar aromatic core to quench the emission. We here reported a novel strategy to achieve luminescent liquid crystals based on perylene bisimides by introducing a conformation-adjustable core to control the molecular stacking arrangement of planar perylene bisimides in the solid state. The emission wavelength is in the deep-red region with a luminescence efficiency of up to 10%. Fluorescence properties of the liquid crystals can be further regulated by photoisomerization-induced structural evolution from columnar to lamellar mesophases. These luminescent liquid crystals are also able to not only exhibit strong emission at high temperatures but also show attractive thermochromic luminescence tuning behaviors. This work provides a new strategy for the design and development of novel solid-state luminescent materials with potential for various optoelectronic applications.

Electro-Thermochromic Luminescent Fibers Controlled by Self-Crystallinity Phase Change for Advanced Smart Textiles.

Smart textiles with tunable luminescence have received special attention due to their great potential in various advanced photonic applications. Particularly, the development of one-dimensional, on-demand, responsive fluorescence fibers with excellent adaptability is of great significance. Herein, we propose electro-thermochromic fluorescence fibers regulated by a self-crystallinity phase change; that is, their tunable luminescence properties are derived from the reversible conversion of the dispersion state and fluorescence emission of fluorophore molecules during the crystallization/melting processes of phase-change materials. First results obtained with an alginate wet-spinning system demonstrate that the self-crystallinity phase change can produce polymeric fibers with thermochromic fluorescence behavior, which are prepared using microemulsion particles containing a phase-change fatty acid and coumarin fluorescent dyes. These thermochromic fluorescence fibers possess a fast response speed, high emission contrast, and good reversibility (>100 cycles). Particularly, the thermochromic fluorescent fibers can gain an electrotriggered capability by means of electric heating materials, and their great potential in precision operation applications is demonstrated. It is easy to adjust the switching point of the electro-thermochromic fluorescence fibers, highlighting their potential use in a diverse range of applications, the designs of which can be personalized. This work offers a simple yet versatile strategy for constructing electro-thermochromic fluorescence fibers for advanced smart textiles.

Thermally Hypsochromic or Bathochromic Emissions? The Silver Nuclei Does Matter.

Structural modulation of core-shell silver nanoclusters from the inside is a huge challenge but of great importance in their syntheses. Herein, two silver nanoclusters [Ag3 S9 @Ag42 ] (SD/Ag45b) and [Ag9 S9 @Ag42 ] (SD/Ag51a) are isolated in the presence of different kinds of sulfonic acids. Uniquely, SD/Ag45b and SD/Ag51a show typical core-shell structures with the similar Ag42 shell but different cores. The outer shell of 42 silver atoms comprises two Ag3 trigons at two poles encircled by three equatorial distorted square cupolas (J4 , Ag12 ). The core in SD/Ag45b is a silver trigon ligated by nine S2- ions (Ag3 S9 ), while a tricapped triangular prismatic Ag9 also ligated by the same amount of S2- ions (Ag9 S9 ) is observed in the inner core of SD/Ag51a. The electrospray ionization mass spectrometry (ESI-MS) indicates that the introduction of p-toluenesulfonic acid can realize the transformation from SD/Ag45b to Ag51 . SD/Ag45b and SD/Ag51a show inverse luminescence thermochromic behaviors in the near-infrared (NIR) region, mainly dictated by the inner silver cores. This work not only realizes the synthesis of new silver nanoclusters by core modulation but also provides a prototype to get molecular-level insight into the correlation between structure and luminescence thermochromism.

A Quasi‐Two‐Dimensional Copper Based Organic‐Inorganic Hybrid Perovskite with Reversible Thermochromism and Ferromagnetism

AbstractTwo‐dimensional (2D) organic‐inorganic hybrid perovskites (OHPs) have been gaining more and more attention for their unique optical, electrical and magnetic behaviors. Herein, we report a multifunctional quasi‐2D hybrid perovskite, 1, 6‐hexanediammonium tetrachlorocuprate ((1, 6‐HDA)CuCl4), which exhibit reversible thermochromic behavior, temperature‐dependent conductivity and ferromagnetism. Changing temperature results in the reversible color change of (1, 6‐HDA)CuCl4 between yellow and brown. A screen‐printing ink is prepared by using (1, 6‐HDA)CuCl4 and used to print thermochromic patterns. The reversible thermochromism originates from the CuCl6 octahedron distortions and lattice expansion in the crystal structure. The conductivity varies more than two orders of magnitude upon temperature change. (1, 6‐HDA)CuCl4 also shows ferromagnetic property with Curie temperatures around 12 K.

Lanthanide-based complexes as efficient physiological temperature sensors

A new molecular thermometric sensor based on the terbium(III) complex [C2mim][Tb(fod)4] (C2mim – 1-methyl-3-ethylimidazolium, fod− - tetrakis-6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionate), doped with 0.015% of its europium(III) analogue (1, [C2mim][Tb(fod)4]0.99985:[C2mim][Eu(fod)4]0.00015), was prepared and its thermochromic behaviour evaluated from ambient temperature up to 75 °C, including in the physiological range (35–45 °C). It was found that the intensity ratio of the 5D4→7F5 (TbIII) and 5D0→7F2 (EuIII) transitions is correlated with temperature having three different linear regimes. Visual colorimetry allowed the evaluation of the temperature in different ranges from green at ambient temperature, to yellow and finally red at higher temperatures. The TbIII complex emission intensity is extremely sensitive to small temperature variations, particularly between 25 and 35 °C, were it reaches only 40% of the initial intensity.Confinement of the dopped TbIII tetrakis-complex in the organic polymeric matrix poly(methylmethacrylate) (PMMA) induced higher thermal stability in 1, together with a strong temperature dependence of the most intense emissive transition of the TbIII complexes. The photoluminescence quantum yield of polymer-lanthanide hybrid materials increased significantly compared with that of 1. Under 366 nm irradiation, the hybrid material presents a green colour at 25 °C that evolves to yellow at 30 °C and to a white tone at 35 °C.

Reversible thermochromic composites for intelligent adjustment of solar reflectance

This paper presents a series of passive intelligent cooling materials with different colors, which can be used to alleviate the heat island effect applying in buildings. The cooling composites with intelligent discoloration and reflectance adjustment were prepared based on low density polyethylene (LDPE). Inorganic particles with different colors and thermosensitive black were introduced into LDPE to satisfy the requirements of color and cooling properties. The chromatic aberration values measured at 25 °C and 35 °C indicate that the variation of color appears on LDPE composites with intelligent color. Taking advantage of the 31 °C discoloration of thermosensitive black, the color of the samples tends to be dimmed at low temperature due to the thermosensitive black appears black, which weakens the reflectance ability of sunlight reducing cooling property and achieves partial heat retention. Above 31 °C, the color of thermosensitive black fades causing the samples to develop color. The bright colors bring higher solar reflectance reducing heat to achieve intelligent cooling. In the outdoor cooling property test, the final temperature of the glass is 65.2 °C while all samples reduce the temperature to 45.6 °C–50.6 °C, performing excellent cooling property. In addition, after thermal aging at 80 °C for 48 h as well as cold and thermal cycle tests (0 °C–80 °C) for 10 times, the composites still have good reversible thermochromic behavior showing excellent thermal aging, durability and reproducibility.

Thermochromism in a dinuclear copper complex by spin state changes at various temperatures

This study explored the thermochromic behavior of [(μ2-6-methyl-2-pyridinemethanolate)2{Cu(6-methyl-2-pyridinemethanol)}2](PF6)2. The complexes show no significant variation between 296 K and 100 K according to a single-crystal X-ray crystallographic investigation. The occupancy of the triplet at 300 K and 100 K is 55% and 16.9%, respectively based on magnetic susceptibility. Photographs of the complex at different temperatures and quantum calculation exhibit that the thermochromic behavior is induced by the alteration of spin state between triplet and singlet.

Hydrogen bonding reversibility in poly(10,12-pentacosadiynoic acid)/titanium dioxide composite analyzed by infrared spectroscopy

In this work, the chromatic behavior of a poly(10,12-pentacosadiinoic acid)/titanium dioxide (TiO2) nanocomposite was studied. Infrared spectroscopy showed that above 55 °C the peak of the carboxyl groups undergoes a shift from 1690 cm−1 (25–55° C) to 1710 cm−1 (≥60 °C), which is reversible after cooling regardless of whether the sample was in the blue or red phase prior to heating. This indicates that the thermochromic behavior and the hydrogen bond shifting are not completely related, since the signal of the hydrogen bond is influenced by temperature, but is reversible; however, the color change is not. Importantly, TiO2 does favor thermochromic reversibility, unlike that indicated in previous reports. Computational chemistry showed that the effect of temperature on a polydiacetylene oligomer with three repeating units produces torsion, which directly impacts the strength of the hydrogen bonds between the carboxyl groups, coinciding with the experimental work.

Moisture-stimulated reversible thermochromic CsPbI3-xBrx films: In-situ spectroscopic-resolved structure and optical properties

We report a composition-dependent, moisture-stimulated reversible thermochromic phenomenon in CsPbI3-xBrx (0 ≤ x ≤ 2) films. The mechanism for the thermochromism is attributed to a reversible phase transition between perovskite (H-T phase) and nonperovksite (L-T phase) structure with the transition temperature points dependent on the I/Br ratio. Temperature and composition dependent thermochromic behavior of the films was recorded via in-situ x-ray diffraction, spectroscopic ellipsometry and digital photography in heating process. The color of the film changes from black to dark red with increasing Br content of 0 ≤ x ≤ 2 for the H-T phases, while chromically changed into yellowish-gray (semitransparent) to reddish-gray (transparent) for that of L-T phase. The three representative compositions of x = 0, 1, and 2 were selected as modelling compositions to illustrate the temperature-dependent opitcal constants evolution. We found two linear relationships: (i) TL-T→H-T=-80x+340(°C) for the phase transition point, and (ii) ΔEgCsPbI3-xBrx=0.17x+1.76(eV) for the bandgap evolution with composition. The composition dependent phase evolution and temperature-dependent optical parameters in CsPbI3-xBrx family not only provide the fundamental structure and thermal stability data for further understanding the relationship between composition and physical properties, but also important for the design and fabrication of effective devices for the promising optical, optoelectronic and thermochromic applications.

Reversible thermochromic behavior and mechanism of Congo red/palygorskite nanohybrid induced by mechanochromism

Reversible thermochromic behavior and mechanism of Congo red/palygorskite nanohybrid induced by mechanochromism

Phase changing poly(ionic liquid) with electrolytic functionality for a single-layer ionogel-based smart window with multi-stimuli response

Functional materials play a crucial role in the design of smart windows that can provide a more comfortable indoor environment for people to enjoy a better lifestyle. A traditional smart window material tends to have only a single feature wherein the color change is led by solar energy input. It was known that different color tones have a significant influence on people's emotions. Herein, our group has adopted a strategy to combine the properties of an electro- and thermo-chromic in a single layer (all-in-one) ionogel. In this work, 3-chloro-N-isopropylacetamide containing thermo-responsive poly [VNIm][TFSI] based electroactive has been synthesized for multi-responsive device. Ionogel, consisting of MBV [TFSI], ferrocene, and poly [VNIm][TFSI], was utilized to construct a single layer (all-in-one) device (with and without water). The proposed ionogel based device 1 (with water) that could offer a useful response to surrounding environments by switching between opaque and transparent in the aqueous condition through a temperature change. This kind of device 1 can be utilized as an individual privacy smart windows, under specific conditions. On the other hand, the ionogel based device 2 (without water) exhibits remarkable electrochromic performance through a reversible color change between colorless to purple color once 1.8 V was applied at 25 °C (below UCST) and gave a high (ΔT) of 74.9% and a coloration efficiency (CE) of 229.03 cm2 C−1 with coloration and bleaching times of 10.2 s and 100 s, respectively, while the tone changes from purple to blue when the device 2 is above UCST (52 °C). These phenomena are caused by the synergetic effect of its electrochromic reaction and thermochromic behavior. The device 2 maintained its switching stability for >2000 cycles. This novel strategy of integrating thermo- and electrochromic materials into a single device will lead to the development of the next generation of multifunctional smart windows.