Reversible Thermochromic Behavior Research Articles

Rapid, Direct Fabrication of Thermochromic Ceramic Composite Sensors via Flash Lamp Annealing

An inorganic, high‐temperature (≈600 °C) thermochromic sensor is synthesized from a chemically bonded ceramic composite. The ceramic composite is composed of thermochromic 10 wt% chromium‐doped alumina (Cr:Al2O3) powder blended with a low‐reacting temperature (around 250 °C) phosphate binder, Al(H2PO4)3, (aluminum dihydrogen phosphate [ADP]). Cr‐doped alumina exhibits thermochromism at high temperatures, typically around 500–600 °C. Previously, infrared (IR) irradiation has been used to successfully convert ADP to an aluminum phosphate (AlPO4) ceramic phase that can bind ceramic components together. Here, an ultrahigh‐power (tens of kilowatts per square centimeter) flash lamp annealing (FLA) system is evaluated as an alternative photonic heating process to rapidly transform ADP to this ceramic. While IR lamps require 30 min to fully transform the ADP binder, FLA processes require less than 1 min and provide more dense microstructures, opening opportunities to additively manufacture ceramic components without the need for a post‐processing heating step. Final ceramics exhibit reversible thermochromic behavior, transitioning from pink to dark gray as the temperature increases from 25 to 600 °C. Here, the ability to use this technology to fabricate a temperature warning system for heated objects that are not yet emitting significant visible black‐body radiation is demonstrated.

Reversal in solvatochromism, photochromism and thermochromism in a new bis-azo dye based on naphthalen-1-amine

A novel bis-azo dye, 4,4′-((1E,1′E)-(oxybis(4,1-phenylene))bis(diazene-2,1-diyl))bis(naphthalen-1-amine) (abbreviated as 4odna) was synthesized and characterized by IR and 1H, 13C and 2D COSY-NMR spectroscopies, and mass spectrometry. Optical properties were evaluated using UV–vis absorption spectroscopy. The observed solvatochromism was ascribed to the presence of different azo or/and hydrazone forms in solution. The azo forms show both positive and negative solvatochromism, with the reversal occurring for solvents with ET(30) ∼45 kcal mol−1, while the hydrazone tautomer shows negative solvatochromism. Application of the multiparametric Catalán and Kamlet-Taft linear solvation energy models allowed to evaluate the dependence of the solvatochromism exhibited by 4odna on the hydrogen bond donating (HBD) and accepting (HBA) abilities of the solvent, as well as on their dipolarity (SdP) and polarizability (SP). Upon UV (λ = 311 nm) irradiation at room temperature, the compound was found to exhibit similar photochromic behavior in the polar-protic solvents methanol and ethanol, which is distinct from that observed in the polar-aprotic solvents dichloromethane, chloroform and chlorobenzene, with the hydrazone tautomer being photoconverted into the azo tautomer in the first group of solvents and vice-versa in the second group. In acetone, UV irradiation extensively transforms the compound into species with no absorption in the visible range, leading to fast discoloration of the solution. Temperature dependence of the color of the solutions of 4odna in ethanol and chlorobenzene was also evaluated, and reversible thermochromic behavior was observed in the first solvent. In chlorobenzene, no thermochromism was observed, but a change of color of the solution was promptly induced by the UV–vis broadband source beam of the spectrometer when the absorbance spectrum of the solution was being recorded at T = 115 °C, which demonstrates that the azo forms of 4odna undergo easy phototransformation into the hydrazone forms in this solvent at high temperature.

Reversible Thermochromism and Stable Resistance Switching Behaviors Based on a Co(III)-Complex-Linked Polyoxoniobate.

A 3D Co(III)-complex hybrid polyoxoniobate framework Na10(H2O)36[Co2(phen)2(4,4'-bipy)(Nb6O19)2]·19H2O (1) has been constructed from [Co2(phen)2(4,4'-bipy)(Nb6O19)2]10- dimer units and 2D inorganic Na-O cluster layers. The Co(III) centers are coordinated with {Nb6O19}, 4,4'-bipy and phen simultaneously. The [Co2(phen)2(4,4'-bipy)(Nb6O19)2]10- fragments link the Na-O cluster layers to generate a 3D metal complex-modified hybrid polyoxoniobate framework with π-π interactions between phenanthroline rings. Compound 1 shows reversible thermochromic behavior resulting from electron transfer from {Nb6O19} to 4,4'-bipy and subsequent formation of radical products, which is first observed in polyoxoniobates. Furthermore, the compound exhibits stable nonvolatile storage behavior and rewritable resistive switching with a low switching voltage (1.12 V) and high current on/off ratio (1.18 × 103) along with stable cyclic performance during stability test for 200 cycles. Charge-transfer mechanism has been studied by analyzing the relationship between current and voltage in the process of resistance switching.

Macrocyclic NiII-Xanthate [NiII2-µ2-bis-{(κ2S,S-S2COCH2CH2)2N(Ts)}] Complex and a Cyclic Thiocarbonate Monomer: Synthesis, Crystallography, Photophysical, TD-DFT and Investigation of Thermochromism

Potassium salt of N,N-Bis(2-dithiocarbonatoethyl)-4-methylbenzenesulfon amide (K2xan) was synthesized and characterized prior to use in the progress of a 24-membered binuclear metallomacrocyclic compound [NiII2-µ2-bis-{(κ2S,S-S2COCH2CH2)2N(Ts)}] (1) and a synthetically challenging 16-member organic functional macrocycle 6,14-ditosyl-1,3,9,11-tetraoxa-6,14-diaza-cyclohexadecane-2,10-dithione (2). Compounds have been characterized by using microanalysis, standard spectroscopic and crystallographic techniques. A plausible mechanism for the formation of compound 2 has been established based on experimental evidence. Compounds 1 and 2 fluoresces at 377 and 293 nm upon excitation at 314 and 232 nm, respectively. The single crystal X-ray diffraction (SCXRD) study revealed a distorted square planar coordination geometry around NiII-centre in 1 which is consistent in the solution of non-coordinating solvents such as CH2Cl2. In a coordinating solvent such as DMSO, however, charge transfer bands 421, 481 nm vanished and characteristic d-d transition band at 698 nm appeared which suggest a change in the coordination geometry around NiII centre from square planar (in CH2Cl2) to octahedral complex (in DMSO). This solvatochromic behaviour of NiII-xanthate complex 1 is supplemented by reversible thermochromic behaviour over a wide temperature ca 30–90°C. Notably, thermal degradation of NiII-xanthate complex 1 gave a stable residual mass that corresponds to NiS. The X-band EPR, UV–visible and TD-DFT studies and electrochemical investigations have been performed to rationalize the results and establish the structure-property correlation.

Preparation and performance of reversible thermochromic phase change microcapsules based on negative photochromic spiropyran

Thermochromic phase change materials have been widely studied for their importance in energy-efficient buildings, thermal control clothing, and low-temperature energy storage. Herein, we successfully designed and synthesized a spiropyran compound with negative photochromic properties in a solid matrix, 3-(3′,3′-dimethyl-6,8-dinitrospiro[chromene-2,2′-indolin]−1′-yl) propyl methacrylate (SPMA), as a thermochromic dye. The synthesized spiropyran was copolymerized with methyl methacrylate (MMA) using photoinitiation, and then n-octadecane was encapsulated by the copolymer to prepare reversible thermochromic phase change microcapsules (TC-microPCMs) through the solvent evaporation technique. The encapsulation efficiency of n-octadecane by copolymers prepared with different photoinitiator concentrations was also investigated. According to the results of SEM, particle size analysis (DLS), and DSC, the copolymer prepared at 3% concentration possessed the best encapsulation effect on n-octadecane, and the melting enthalpy of the microcapsules reached 168.7 J/g and the encapsulation ratio was 89.5%, which was not significantly different from that of microcapsules without the addition of thermochromic dyes. This di-functionalization process effectively avoids the "impurity effect" of dye addition. In addition, the homogeneous spherical structure and stable chemical composition of the microcapsules are the key factors to achieve a fully reversible thermochromic behavior. What's more, the functionalized film based on TC-microPCMs, TC-microPCMs@PVA, was used to explore the potential for applications in thermal storage and temperature sensing. The results demonstrated that the composite film has excellent reversible thermochromic performance, high latent heat storage performance, and good cycling durability, which make the bifunctional microcapsules highly promising candidates for thermal sensors, solar energy storage, and smart textiles.

Large-scale synthesis of macroscopic layered inorganic-organic hybrid nanobelt aerogel monoliths with multifunctionality

Fabrication of freestanding nanostructured aerogel monoliths with multifunctionality on a large scale represents a great challenge due to the limited scalable methods for synthesis and assembly of multi-component nanostructures into one single gel body. Here, we report a scalable solvothermal-based in situ gelation method for synthesizing mechanically stable cobalt-based layered inorganic-organic hybrid nanobelt (Co-LIOHN) aerogel monoliths with a density as low as 2.8 mg/cm 3 , an ultralow thermal conductivity of 25 mW/(mK), and extraordinary adsorption capacities of 51–145 g/g for various solvents. Moreover, the aerogel exhibits reversible thermochromic behavior originating from the changing of the coordination environment of the Co 2+ caused by the loss and uptake of coordinating molecular water upon heating and cooling. The Co-LIOHN aerogels integrate unique features of the aerogel and intrinsic properties of the hybrid nanobelts, giving access to a truly multifunctional material that has great potential for applications in thermal insulation, environmental remediation, sensing, and camouflage. • A scalable in situ gelation method is developed for producing Co-LIOHN aerogels • The gelation is enabled by self-crosslinking of nanobelts via van der Waals forces • The Co-LIOHN aerogel shows excellent oil removal and thermal insulation capability • The Co-LIOHN aerogel demonstrates unprecedented thermochromic properties Li et al. report a facile and scalable in situ gelation method for the fabrication of macroscopic freestanding cobalt-based layered inorganic-organic hybrid nanobelt aerogel monoliths that exhibit outstanding oil removal, thermal insulation, and thermochromic properties.

Thermochromic SmNiO3-δ thin films deposited by magnetron sputtering and crystallized by soft-annealing in air

Samarium nickelate (SmNiO3) exhibits a metal-insulator transition (MIT) around 120 °C and therefore appears to be an excellent candidate for a new generation of thermochromic solar absorbers. Nevertheless, this kind of perovskite is classically obtained under extreme conditions to stabilize the metastable Ni3+ oxidation state. Here, we show that SmNiO3-δ thin films can be synthesized under soft-annealing as the habitual orthorhombic distorted perovskite structure. The layers were deposited by reactive magnetron co-sputtering and subsequently annealed for crystallization for 2 h at 500 °C in air. Structural characterization was carried out using X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques, while optical and electrical properties were determined by Fourier transform infrared spectroscopy (FTIR) and the four-point probe method, respectively. The Ni3+ ion was confirmed by Electron energy loss spectroscopy (EELS). Finally, reversible thermochromic behavior was observed with an MIT temperature estimated at 138 °C and an IR contrast of 19%.

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.

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.

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.

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

Mechanochromism, thermochromism, protonation effect and discrimination of CHCl3 from organic solvents in a Et2N-substituted Salicylaldehyde Schiff base

Multi-stimuli-responsive materials, which can show color/fluorescence change in response to external chemical or physical stimuli, have received increasing attention due to the capacities for facile realization of multifunctional sensing. Herein, we presented a Et2N-substituted salicylaldehyde Schiff base compound (DDHAC) with multi-stimuli-responsive behaviors. An investigation of the photophysical properties in solution demonstrated DDHAC was an excited-state intramolecular proton transfer (ESIPT) and aggregation-induced emission (AIE) active molecule. Owing to structural flexibility from salicylaldehyde Schiff base, the compound displayed reversible mechanochromic and thermochromic behavior, which were associated with the crystalline-to-amorphous and crystalline-to-crystalline, respectively. Moreover, the Et2N group endowed DDHAC with the capability that response of protonation. Due to its protonation effect, DDHAC could serve as a unique optical probe for discriminating CHCl3 from organic solvents assisted by UV irradiation. The selectivity was attributed to the interaction of DPPTP with HCl gas from photodecomposition product of chloroform.

Reversible and Irreversible Thermochromism in Copper‐Based Halide Perovskites

AbstractCopper‐based layered perovskites have shown abundant phase transitions and thermochromic behaviors. However, there are very few cases of perovskites with irreversible transitions. Here, the thermochromic behavior of two perovskites (CEA)2CuCl4 and (BEA)2CuCl4 is discussed, where CEA = 2‐chloroethylammonium and BEA = 2‐bromoethylammonium, the latter of which is reported for the first time. These materials exhibit a reversible and irreversible thermochromic behavior determined by the nature of the organic cation. Using nuclear magnetic resonance, X‐ray diffraction, and optical absorption, it was possible to investigate the mechanism for this transition: a topochemical exchange reaction between the organic and inorganic halides in (BEA)2CuCl4 to yield the mixed‐halide perovskite (BEA)1.1(CEA)0.9CuCl3.1Br0.9. These materials and the fundamental principles shown herein have potential use as low‐cost irreversible thermochromic sensors and their design.

Exploring Reversible Thermochromic Behavior in a Rare Ni(II)-MOF System.

Thermochromic metal-organic frameworks (MOFs) are promising functional materials for a wide range of applications due to their ability to exhibit color variation under external temperature stimuli, yet the development of them with high cyclability and efficient regeneration processes remains challenging. Here, presented is a rare example of an ultrastable Ni(II)-MOF exhibiting an unprecedented reversible four-step color change between two complementary colors in a wide temperature range, which could be repeated for at least 500 cycles without losing crystallinity and thermochromic performance. Notably, the regeneration can be achieved within 1 min by simply letting the crystals cool naturally in the air, facilitated by the unique nature of the channels' inner surface. The reversible thermochromic behavior is owing to a series of reversible crystal structure changes with temperature, including the stepwise dehydration/rehydration process, and structural changes. This work facilitates the future development of more MOF-based reversible thermochromic materials with excellent performance and improved practical applicability.

Reversible Thermochromic Superhydrophobic BiVO4 Hybrid Pigments Coatings with Self-Cleaning Performance and Environmental Stability Based on Kaolinite.

The inferior acid resistance and high cost of BiVO4 pigments seriously hinder their wide applications in some fields. Inspired by the superhydrophobic properties of some plants and insects in nature, the reversible thermochromic superhydrophobic coatings with self-cleaning performance and environmental stability were successfully designed by combining with the surface roughness of kaolinite/BiVO4 hybrid pigments (Kaol/BiVO4-HP) and the modification with hexadecyltrimethoxysilane (HDTMS). When the concentration of HDTMS was 4.58 mmol/L, the yellow superhydrophobic coatings exhibited excellent self-cleaning properties and chemical and environmental stability. Furthermore, the superhydrophobic Kaol/BiVO4-HP coatings exhibited the reversible thermochromic behavior with the change of the external temperatures from room temperature to 270 °C. Interestingly, this facile strategy also can be used to fabricate a series of superhydrophobic clay mineral/BiVO4-HP coatings based on the different clay minerals, and there was no relationship between the superhydrophobic properties of the coatings and the morphologies of clay minerals, which was different from the reported color superhydrophobic coatings prepared with Maya-like blue pigments. Thus, the low-cost and thermochromic superhydrophobic clay mineral/BiVO4-HP coatings presented a promising application in temperature sensors and switches with the excellent weather resistance to record and monitor the temperature changes.

Vapor-, thermo-, and mechanical-grinding-triggered tri-stimuli-responsive luminescence switching of cycloplatinated(II) complex bearing 8-quinolinol derivatives

Four novel cycloplatinated(II) complexes, Pt(ppy)(L1) (1), Pt(ppy)(L2) (2), Pt(ppy)(L3) (3) and Pt(ppy)(L4) (4) based on 5-[2-(4-substituent-phenyl)ethynyl]-8-quinolinol ligands {substituent = H (L1), Me(L2), Et(L3), t-Bu(L4)} were synthesized and characterized. Complex 4 has three main pseudopolymorphs, including orange 4·CH3CH2OH, red 4R, and dark-brown 4·½(CCl4). Complex 4 exhibits interesting tri-stimuli-responsive luminescence switching properties. Upon exposure to different VOC vapors, three pseudopolymorphs display unusual irreversible vapoluminescence that 4R and 4·½ (CCl4) can be exchanged with each other and be irreversibly converted to 4·CH3CH2OH. Furthermore, 4·½(CCl4) shows reversible thermochromic luminescence behaviour and can be reversibly converted to 4R upon heating. No detectable change in color and luminescence of 4·CH3CH2OH and 4R can be found during the heating process, although 4·CH3CH2OH lost its solvent and changed to desolvated 4O. In addition, 4·CH3CH2OH, and 4·½ (CCl4) also show the mechanoluminescent property that both of them will be converted to the same red amorphous 4G peaked at 742 nm after grinding. Systematic studies revealed that the tri-stimuli-responsive luminescence switching property of 4 is due to the structural conversion and resultant changes of the lowest-energy excited states. In contrast, complexes 1–3 have not any luminescent switching property. The reason is most likely due to the compact stacking structures of them which prevent their structural conversion triggered by external stimuli.

Development of reversible and durable thermochromic phase-change microcapsules for real-time indication of thermal energy storage and management

We reported a design of novel thermochromic phase-change microcapsules (TCMs) with a sandwich-structured shell for reversible and durable indication of thermal energy storage and management in real-time. Two types of TCMs with red and blue color indicators were successfully constructed by fabricating a silica base shell onto the n-docosane core, followed by formation of a thermochromic indication layer and a polymeric protective layer, and their multilayered configuration and well-defined core-shell structure were confirmed by microstructural investigation and chemical composition analysis. These two types of TCMs not only showed an outstanding latent heat-storage/release capability with a high capacity over 150 J/g, but also exhibited a good shape stability, high thermal stability and excellent phase-change reversibility and durability. The optimum operation conditions for thermal energy charge/discharge were also determined by nonisothermal and isothermal differential scanning calorimetric analyses. Most of all, the two types of TCMs presented an entirely reversible thermochromic behavior individually with high-contrast red and blue color indications for the phase-change state of n-docosane core. Both of them exhibited high reversibility and long cycle life in thermochromic indication, which meets the design requirements for durable indication of latent heat storage and thermal management in real-time. In the light of an innovative configuration of sandwich-structured shell and a smart combination of latent heat-storage and thermochromic functions, the TCMs designed by this study has a great potential for applications in smart fibers and textiles, wearable electric devices, energy-saving buildings, temperature-sensitive medical system, safety clothing, smart windows, aerospace engineering and many more.

A reversible thermo-responsive 2D Zn(ii) coordination polymer as a potential self-referenced luminescent thermometer

A two dimensional Zn(ii) coordination polymer with exceptional reversible luminescence thermochromic behavior has been synthesized for temperature sensing applications.

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)2 CuCl6 , which show reversible thermochromic behavior, dramatic temperature-dependent conductivity change, and strong ferromagnetism. Upon temperature change, the (PED)CuCl4 and (BED)2 CuCl6 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)2 CuCl6 exhibits superior thermal stability, with a thermochromic working temperature up to 443 K. The conductivity of (BED)2 CuCl6 changes over six orders of magnitude upon temperature change. The 2D perovskites exhibit ferromagnetic properties with Curie temperatures around 13 K.

Reversible Thermochromism and Strong Ferromagnetism in Two‐Dimensional Hybrid Perovskites

AbstractTwo‐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.