Rational design of photofunctional dyes BODIPYs/aza-BODIPYs and applications for photocatalysis, photoelectric conversion and thermochromic materials

4,4-Difluoro-4-bora-3a,4a-diaza-sindacene (BODIPY) is a sort of photofunctional dye which possesses advantages including strong light-capturing property, high photon-resistance, etc. Meso-N substituted aza-BODIPY is a crucial derivative of BODIPY scaffold that has the favorable optical properties and a significant spectral redshift. The photophysical properties can be tuned by molecular design, and the attenuation path of the excited state energy release of absorbed light energy can be well controlled via structural modifications, enabling tailored application. It has been extensively employed in life medicine fields including fluorescence imaging diagnosis, photodynamic therapy photosensitizer and photothermal therapy reagent and so forth. Extensive research and review have been performed in these areas. However, BODIPYs/aza-BODIPYs have a significant role in energy, catalysis, optoelectronics, photo-responsive materials and other fields. Nevertheless, there are relatively few studies and reviews in these fields on the modification and application based on BODIPY/aza-BODIPY scaffold. Herein, in this review we summarized the application of BODIPY/aza-BODIPY in the aforementioned fields, with the molecular regulation of dye as the foundation and the utilization in the above fields as the objective, in the intention of providing inspiration for the exploration of innovative BODIPY/aza-BODIPY research in the field of light resource conversion and functional materials.

A Thermochromic, Viscoelastic Nacre-like Nanocomposite for the Smart Thermal Management of Planar Electronics

Cutting-edge heat spreaders for soft and planar electronics require not only high thermal conductivity and a certain degree of flexibility but also remarkable self-adhesion without thermal interface materials, elasticity, arbitrary elongation along with soft devices, and smart properties involving thermal self-healing, thermochromism and so on. Nacre-like composites with excellent in-plane heat dissipation are ideal as heat spreaders for thin and planar electronics. However, the intrinsically poor viscoelasticity, i.e., adhesion and elasticity, prevents them from simultaneous self-adhesion and arbitrary elongation along with current flexible devices as well as incurring high interfacial thermal impedance. In this paper, we propose a soft thermochromic composite(STC) membrane with a layered structure, considerable stretchability, high in-plane thermal conductivity(~30 Wm^(-1) K^(-1)), low thermal contact resistance(~12 mm^2 KW^(-1), 4–5 times lower than that of silver paste), strong yet sustainable adhesion forces(~4607 Jm^(-2), 2220 Jm^(-2) greater than that of epoxy paste) and self-healing efficiency. As a self-adhesive heat spreader, it implements efficient cooling of various soft electronics with a temperature drop of 20℃ than the polyimide case. In addition to its self-healing function, the chameleon-like behavior of STC facilitates temperature monitoring by the naked eye, hence enabling smart thermal management.

Thermochromic Silks for Temperature Management and Dynamic Textile Displays

Silks have various advantages compared with synthetic polymer fibers,such as sustainability,mechanical properties,luster,as well as air and humidity permeability.However,the functionalization of silks has not yet been fully developed.Functionalization techniques that retain or even improve the sustainability of silk production are required.To this end,a low-cost,effective,and scalable strategy to produce TCSs by integrating yarn-spinning and continuous dip coating technique is developed herein.TCSs with extremely long length(>10 km),high mechanical performance(strength of 443.1 MPa,toughness of 56.0 MJ m−3,comparable with natural cocoon silk),and good interfacial bonding were developed.TCSs can be automatically woven into arbitrary fabrics,which feature super-hydrophobicity as well as rapid and programmable thermochromic responses with good cyclic performance:the response speed reached to one second and remained stable after hundreds of tests.Finally,applications of TCS fabrics in temperature management and dynamic textile displays are demonstrated,confirming their application potential in smart textiles,wearable devices,flexible displays,and human–machine interfaces.Moreover,combination of the fabrication and the demonstrated applications is expected to bridge the gap between lab research and industry and accelerate the commercialization of TCSs.

Thin film design for advanced thermochromic smart radiator devices

This paper describes the research on the materials and design methods for advanced smart radiator devices （SRDs） on large-area flexible substrates utilized on spacecraft. The functional material is thermochromic vanadium dioxide. The coating design of SRD is similar to the design of broadband filter coatings in a mid-infrared region. The multilayer coatings have complex structures. Coating materials must be highly transparent in a required spectrum region and also mechanically robust enough to endure the influence from the rigorous environments of outer space. The number of layers must be very small, suitable for the deposition on large-area flexible substrates. All the coatings are designed initially based on optical calculation and practical experience, and then optimized by the TFCALC software. Several designs are described and compared with each other. The results show that the emittance variability of the designed SRDs is great than 400%, more advanced than the reported ones.

Synthesis, Thermochromic Properties and Thermal Behavior of some Schiff Bases.Part I. p,p'-Diaminodiphenylmethane-Schiff Bases and Sulphonamide Schiff Base

p,p'-Diaminodiphenylmethane-Schiff bases (SB) of general formula (R)-phCH=N- ph-CH2-ph-N=CHph(R), where R is p-NO2, m-NO2, p-OH, o-OH, p-Cl, -H, p-OCH3, and sul- phonamide Schiff bases (SB) of general formula (R)-phCH=N-ph-SO2NH2, where R is p-NO2, m-NO2, p-OH, o-OH, p-Cl, -H, p-OCH3, were synthesized and their structure have been characterized by the melting pointing, 1HNMR, MS, and elemental analysis. They are thermolabile and undergo thermo-chromism and thermal decomposition after melting. The TG. and DSC measurement were recorded in dynamic air and interpreted.

Development of thermochromic strips as a water pasteurization indicator

Boiling of water, for purification, commonly practiced in the world, has many problems associated with it like danger of scalding, scaling in the vessels, removal of useful minerals and blandness of taste etc. Water can be made safe for drinking simply by heating at 65℃ for 6 minutes. A colour indicating strip was developed which changes colour from red to purple at 67℃. Use of this strip can help in pasteurizing water without the above problems and with considerable energy saving.

Gold Nanoparticles/Thermochromic Composite Film on Screen-Printed Electrodes for Simultaneous Detection of Protein and Temperature

In this study, gold nanoparticles and thermochromic composite films modified screen-printed carbon electrodes (TM-AuNPsSPCEs) were developed as a platform for the simultaneous detection of protein and temperature. The TM-AuNPs composited film had better sensitivity resulting from the gold nanoparticles amplification effect. A phase transition model analysis of TM-AuNPs films found that the TM-AuNPs films had three-phase transition intervals (<45℃, 45℃ to 80℃ and >80℃) which accommodated the temperature requirements for protein denaturation. When used to detect different concentrations of haemoglobin (Hb) solution, the TM-AuNPs modified SPCEs had a better sensitivity in detecting the different concentrations in comparison to TM and AuNP modified SPCEs which showed no clear sensitivity towards the different Hb concentrations. The dual detection and excellent sensitivity show a good application prospect for the study of the TM-AuNPs composite film.

The Effect of Transition Hysteresis Width in Thermochromic Glazing Systems

Thermochromic glazing theoretically has the potential to lead to a large reduction in energy demand in modern buildings by allowing the transmission of visible light for day lighting whilst reducing unwanted solar gain during the cooling season, but allowing useful solar gain in the heating season. In this study building simulation is used to examine the effect of the thermochromic transition hysteresis width on the energy demand characteristics of a model system in a variety of climates. The results are also compared against current industry standard glazing products. The results suggest that in a warm climate with a low transition temperature and hysteresis width energy demand can be reduced by up to 54% compared to standard double glazing.

THERMOCHROMIC POLYMER MATERIALS

Thermochromic polymers will play an extremely important role in the next future. The physical background of thermochromism and the state of development of thermochromic polymers based on light absorption effects are reported. In detail, the interactions between the polymer matrix and the thermochromic composite - composed of leuco or indicator dyes - are discussed on a molecular level. Thermochromic hydrogels with extremely high transparency, an outstanding switching behavior from colorless to colored or between different colors is presented. Preparation of thermosetting and thermoplastic polymers, including the resulting optical, and, for the first time, the mechanical properties are discussed in relation to matrix tuned high-resistant microcapsules.

Regulation of the order-disorder phase transition in a Cs_(2)NaFeCl_(6) double perovskite towards reversible thermochromic application

Multifunctional lead-free double perovskites demonstrate remarkable potential towards applications in various fields.Herein,an environmentally-friendly,low-cost,high-throughput Cs_(2)NaFeCl_(6) single crystal with exceedingly high thermal stability is designed and grown.It obtains a cubic lattice system in the temperature range of 80-500 K,accompanied by a completely reversible chromatic variation ranging from yellow to black.Importantly,the intriguing thermochromism is proved to own extremely high reproducibility(over 1000 cycles)without a hysteretic effect,originating from its structural flexibility that including(i)the noteworthy distortion/deformation of[NaCl_(6)]5−and[FeCl_(6)]3−octahedra;(ii)order-disorder arrangement transition of[NaCl_(6)]5−and[FeCl6]3−octahedra as the function of temperature.This study paves the way towards a new class of smart windows and camouflage coatings with an unprecedented colour range based on a Cs_(2)NaFeCl_(6) perovskite.

THERMOCHROMIC EFFECTS OF LEUCO DYES STUDIED IN POLYPROPYLENE

A series of thermochromic polypropylene foils were prepared by embedding various leuco dye-developer-solvent systems in the polymer matrix. Bisphenol A, laurylgallate, ethylgallate and p-hydroxybenzoic acid methyl ester were used as developers, crystal violet lactone and 3,3-bis-（1-n-butyl-2-methyl-3-indolyl）-phthalide as dyes and l-octanoic acid methyl ester as solvent. The molar ratio between the three components of the investigated leuco dye-developer-solvent systems was kept constant. All obtained polypropylene foils exhibit an excellent thermochromic behavior. The foils, prepared by extrusion technology, switch from color to colorless with increasing temperature. The influence of molecular structure of the developer on the intensity of the colored state and the influence of a developer-surfactant complex on the resulting thermochromic properties were investigated. The results are presented and discussed in detail according to a molecular model suggesting that the ring-opening process of the leuco dye is triggered by the formation of dye-developer complexes via H-bondings.

Fabrication of Melamine/Tb^3+-Intercalated Polydiacetylene Nanosheets and Their Thermochromic Reversibility

Polydiacetylene(PDA)is one kind of the conjugated polymer with layered structure,which can serve as a host to accommodate the guest components through intercalation.In these intercalated PDAs,some of them were reported to have a nearly perfect organized structure and perform completely reversible thermochromism.Till now,these reported intercalated PDAs were made by only introducing a single component for intercalation.Here,we chose 10,12-pentacosadiynoic acid(PCDA)as the monomer,of which the carboxyl-terminal groups can interact with either Tb^3+ ions or melamines(MAs).When the feeding molar ratio of PCDA,MA,and Tb^3+ ion was 3:267:1,only Tb^3+ ions were intercalated though excess MAs existed.Such Tb^3+- intercalated poly-PCDA exhibited completely reversible thermochromism,where almost all the carboxyl groups interacted with Tb^3+ ions to form the nearly perfect structure.When the feeding molar ratio of PCDA,MA,and Tb^3+ ion was 3:267:0.6,both Tb^3+ ions and MAs were intercalated.There existed some defects in the imperfect MA-intercalated domains and at the domain boundaries.The MA/Tb^3+- intercalated poly-PCDA exhibits partially reversible thermochromism,where the backbones near the defects are hard to return the initial conformation,while the rest,those at nearly perfect organized domains,are still able to restore the initial conformation.

Infrared Thermochromic Properties of VO_2 Thin Films Prepared through Aqueous Sol-gel Process

The stoichiometric vanadium（IV） oxide thin films were obtained by controlling the temperature, time and pressure of annealing. The thermochromic phase transition and the IR thermochromic property of 400 nm and 900 nm VO2 thin films in the 7.5 μm-14 μm region were discussed. The derived VO2 thin film samples were characterized by Raman, XRD, XPS, AFM, SEM, and DSC. The resistance and infrared emissivity of VO2 thin films under different temperature were measured, and the thermal images of films were obtained using infrared imager. The results show that the VO2 thin film annealed at 550 ℃ for 10 hours through aqueous sol-gel process is pure and uniform. The 900 nm VO2 thin film exhibits better IR thermochromic property than the 400 nm VO2 thin film. The resistance of 900 nm VO2 film can change by 4 orders of magnitude and the emissivity can change by 0.6 during the phase transition, suggesting the outstanding IR thermochromic property. The derived VO2 thin film can control its infrared radiation intensity and lower its apparent temperature actively when the real temperature increases, which may be applied in the field of energy saving, thermal control and camouflage.

Thermochromic and Magnetic Properties of a Copper(Ⅱ)Coordination Compound

Copper complexes that can experience reversible heat-induced dehydration and rehydration in the solid state were rarely reported although thermochromic copper complexes have been widely reported, and their heat-induced magnetic properties have not been studied. We firstly observed the reversible thermochromic phenomena of the known copper（II） complex [Cu（bpy）（OOCCH3）2]n·xn H2O（x = 2.5 or 3; bpy = 4,4＇-bipyridine） in the solid state, which is associated with the dehydration and rehydration processes, and found that heat-induced coloration clearly enhanced the magnetic susceptibility.

Thermochromic Biopolymer Based on Natural Anthocyanidin Dyes

Recently a novel thermochromic poly(lactic acid) (PLA)-composite material was presented. Depending on temperature the incorporated anthocyanidin dye was found to be present either in its neutral or anionic anhydrobase form. A reversible formation of PLA-dye complexes triggered by conformational changes of the polymer backbone was proposed to explain this thermochromic effect. In order to study the influence of the dye structure on the PLA-dye complex formation and on the thermochromic properties of the PLA-composite material a variation of the anthocyanidin dye structure was investigated. The results indicate that a hydroxyl group in 3’-position of the anthocyanidin dye resulting in the presence of adjacent hydroxyl groups is mandatory for the PLA-anthocyanidin dye complex formation and thus for the occurrence of thermochromism.

Exciting broadband thermochromic transmission property opposite to vanadium dioxide in the atmospheric window

The traditional telecommunications band performs poorly in harsh weather conditions due to atmospheric absorption. In recent years, researchers have begun to study optical communication through atmospheric windows, and optical switches are an essential component of optical communication. A broadband atmospheric window optical switch was proposed based on Vanadium dioxide and magnetic polaritons(MP). It is formed by the stacking of two metal-dielectric-metal structures. The simulation results show that the modulation depth can reach 98.38%, and the extinction ratio is 17.93 dB. By calculating the magnetic field, we confirmed that the reason for the “off” mode is the coupling between the different MP modes, while the “on”mode is the excitation of MP. The optical switch we proposed may be applied to radiation cooling and optical satellite communication.

Study on preparation,characterization and application of mixed-colorants thermochromic microcapsules

In order to expand the color-change range and make the discoloration temperature suitable for the daily textiles,a new formulation of mixed-colorants thermochromic core material is designed,in which crystal violet lactone(CVL)is the basic color former,bisphenol A(BPA)is the developer,especially the solvent-based dye and dodecyl dedecanoate are used as the extended dye and the solvent,respectively.Scanning electron microscope(SEM),differential scanning calorimeter(DSC)and thermogravimetric analyzer(TGA)were applied to study the morphology,encapsulation rate,non-isothermal crystallization behavior and thermal stability of the mixed-colorant thermochromic microcapsules(MCTMs)prepared by in-situ polymerization.The results show that MCTMs have good sphericity,uniform particle size,good thermal stability and the encapsulation rate can reach 86.73%.Under the non-isothermal conditions,the encapsulation of formaldehyde-melamine resin wall material can slightly reduce the crystallization rate of the solvent,but does not affect the relative crystallinity,thermal properties and discoloration sensitivity of the core materials.With the variety of ambient temperatures in the range of 20–35℃,the printed cotton fabrics with MCTMs could change color reversibly between different tones with good reliability and durability,and exhibit more gorgeous colors than the common thermochromic materials.

Research paper Air atmosphere available fast one-pot synthesis of VO_(2)nanoparticles with excellent thermochromic properties by a novel liquid-shielding method

As a typical strongly correlated transition oxide,vanadium dioxide(VO_(2))based nanomaterials have drawn many research attentions these years due to the giant metal-to-insulator phase transition(MIPT)at around 68℃.However,due to the complexities of the V-O system and interplays between various vanadium oxide phases,the synthesis of high-quality VO_(2)nanopowders is still fraught with many challenges,especially in air atmosphere.In this paper,we report a novel air atmosphere available liquid-shielding synthesis method for thermochromic VO_(2)nanoparticles,by using low-eutectic molten-salt(LiCl-KCl)as the liquid-state air-insulation medium at elevated temperature and high-pressure pressed VOSO_(4)-KCl pillars immersed in these liquid salts as the precursor.Small amounts of glucose are added to introduce a slight reductive environment,and well dispersed VO_(2)nanoparticles with excellent ther-mochromic properties can be directly synthesized at an ultra-low temperature of 375℃.This feasible and atmosphere-available mass-production method is rarely reported in the related fields,which may provide a novel protocol strategy for the synthesis of high performance thermochromic VO_(2)and other functional oxide powders.

Polyelectrolyte complex-based thermochromic hydrogels containing carbonized polymer dots for smart windows with fast response,excellent solar modulation ability,and high durability

Thermochromic smart windows have gained increasing popularity in light modulation and energy management in buildings.However,the fabrication of flexible thermochromic smart windows with high luminous transmittance(Tlum),tailorable critical temperature(τc),strong solar modulation ability(ΔTsol),and long-term durability remains a huge challenge.In this study,hydrogel-based thermochromic smart windows are fabricated by sandwiching thermochromic hydrogels of polyallylamine hydrochloride,polyacrylic acid,and carbonized polymer dots(CPDs)complexes between two pieces of transparent substrates.Benefiting from the incorporation of nanosized CPDs,the thermochromic hydrogel has an ultrahigh Tlum of~98.7%,a desirableτc of~24.2℃,aΔTsol of~89.3%and a rapid transition time of~3 s from opaque state to transparent state.Moreover,the thermochromic hydrogel exhibits excellent anti-freezing ability,tight adhesion toward various substrates,and excellent self-healing capability.The self-healing capability enables the fabrication of large-area smart windows by welding multiple hydrogel pieces.The smart windows retain their original thermochromic properties after being stored under ambient conditions for at least 147 days or undergoing 10,000 uninterrupted heating/cooling cycles.The model houses with smart windows can achieve a temperature reduction of 9.2℃,demonstrating the excellent indoor temperature modulation performance of the smart windows.

Preparation and Structure-Property Regulation Mechanism of Reversible Thermochromic Polydiacetylene

The thermochromic mechanism and the structure-property regulation principle of reversible thermochromic polydiacetylene(PDA)materials have always been a challenging issue.In this work,a series of diacetylene monomers(m-PCDA)containing phenyl and amide or carboxyl groups were synthesized from 10,12-pentacosadiynoic acid(PCDA)through the esterification or amidation reactions.The effects of the number and the distribution of the functional groups in m-PCDA molecules on their solid-state polymerization capability,and the thermochromic mechanism of their corresponding polymers(m-PDA)were investigated and discussed in detail.The results show that the m-PCDA monomers containing both benzene ring and groups that can form hydrogen bonding interactions have strong intermolecular interaction,and are easy to carry out the solid phase polymerization under 254-nm UV irradiation to obtain the corresponding new thermochromic m-PDA materials.The thermochromic behavior of m-PDA depends on its melting process.The initial color-change temperature(blue to red)is determined by the onset melting tem perature,and the temperature range in which reversible color recovery can be achieved by repeat heating-cooling treatment is determined by its melting range.According to the proposed thermochromic mechanism of PDA,various new PDA materials with precise thermochromic temperatu res and reversible thermochromic temperature ra nges can be designed and synthesized through the appropriate introduction of benzene ring and groups that can form hydrogen bonding interactions into the molecular structure of linear diacetylene monomer.This work provides a perspective to the precise molecular structure design and the property regulation of the reversible thermochromic PDA materials.