Organic Electrochromic Materials Research Articles

Performance Optimization for Multicolor Electrochromic Devices: Morphology and Composition Regulation of Inorganic Electrochromic Materials and Selectivity of Ions

AbstractIn recent years, multicolor electrochromic devices (ECDs) have attracted much attention due to their application potential for rich color similar to RGB mode. Although organic electrochromic (EC) materials are widely used in multicolor electrochromism because of their multicolor properties, remarkable weatherability remains challenging. Inorganic EC materials especially transition metal oxide are particularly attractive for excellent weatherability in ECD fabrication. Moreover, by selection of electrolytes, better ionic transfer efficiency can be rendered in the EC process. Although the morphology regulation of the EC film and the selection of electrolytes in the ion transmission layer play important roles in optimizing EC performance and have been extensively studied, a systematic and comprehensive review is lacking. In this review, the morphology regulation of the EC film and selection rules of electrolytes in the multicolor ECDs is focused, and the advantages and disadvantages of existing ways are discussed. The current application of multicolor ECDs is also outlined and it is hoped that this review can contribute some inspiration to designing and improving multicolor ECDs.

Layer-stacked polyaniline/silver nanowire composite film for multicolor electrochromic smart windows with dual-band optical modulation

Dual-band electrochromic smart windows (DESWs) have attracted widely concern for their potential in significantly reducing building energy consumption by selectively controlling near-infrared (NIR) and visible light (VIS) transmittance. However, its monotonous color changes limit its large-scale application. In this study, we designed a DESW based on the layer-stacked polyaniline (PANI)/silver Nanowires (Ag NWs) composite films. When PANI films is stacked layer by layer with Ag NWs, it not only performs dual band regulation, but also exhibits impressive electrochromic performance with rich color conversions (light yellow, yellow-green and blue-black). The four-layer PANI/Ag NWs composite film outperformed the pure single-layer PANI film because of the faster electron transfer, its coloring time and bleaching time at 525 nm were shortened to 6.7 s and 18.0 s, respectively, and the coloring efficiency was increased to 45.5 cm2 C-1. After 2500 cycles, the PANI/Ag NWs films tend to have better cycle stability. Therefore, the incorporation of Ag NWs enhances the electrochromic performance of PANI films, providing valuable insights for advancing single-component organic electrochromic materials.

Smart Lipid Nanoparticle that Remodels Tumor Microenvironment for Activatable H2S Gas and Photodynamic Immunotherapy.

Hydrogen sulfide (H2S) has shown promise for gas therapy. However, it is still controversial whether H2S can remodel the tumor microenvironment (TME) and induce robust antitumor immunity. Here, a tumor-targeting and TME-responsive "smart" lipid nanoparticle (1-JK-PS-FA) is presented, which is capable of delivering and releasing H2S specifically in tumor tissues for on-demand H2S gas and photodynamic immunotherapy. 1-JK-PS-FA enables a burst release of H2S in the acidic TME, which promptly reduces the embedded organic electrochromic materials and consequently switches on near-infrared fluorescence and photodynamic activity. Furthermore, we found that high levels of H2S can reprogram the TME by reducing tumor interstitial fluid pressure, promoting angiogenesis, increasing vascular permeability, ameliorating hypoxia, and reducing immunosuppressive conditions. This leads to increased tumor uptake of 1-JK-PS-FA, thereby enhancing PDT efficacy and eliciting strong immunogenic cell death during 808 nm laser irradiation. Therefore, 1-JK-PS-FA permits synergistic H2S gas and photodynamic immunotherapy, effectively eradicating orthotopic breast tumors and preventing tumor metastasis and recurrence. This work showcases the capacity of H2S to reprogram the TME to enhance H2S gas and immunotherapy.

High-contrast energy-efficient flexible electrochromic devices based on viologen derivatives and their application in smart windows and electrochromic displayers

Electrochromic materials and corresponding devices display reversible optical changes under applied voltage. While inorganic and organic electrochromic materials are extensively studied, enhancing their performance is crucial. This study presents a high-contrast energy-efficient flexible electrochromic device based on viologen derivatives and driven by film solar cell. The aims are to foster applications in smart windows, displays, and energy-efficient technologies. Two symmetric viologen derivatives of 1,1′-bis(4-(dimethylamino) phenyl)- [4,4′-bipyridine]dihexafluorophosphate (DNPV) and 1,1′-bis(4-acetamidophenyl)-[4,4′-bipyridine]dihexafluorophosphate (DAcPV) and two asymmetric viologen derivatives of 1-benzyl-1'-(4-(dimethylamino)phenyl)-[4,4′-bipyridine]dihexafluoro-phosphate (Bn-NPV) and 1-(4-acetamidophenyl)-1′-benzyl-[4,4′-bipyridine]dihexa-fluorophosphate (Bn-AcPV) were synthesized. These viologen derivatives as active materials were used to assemble both flexible and rigid electrochromic devices (ECDs). After applying voltage of 1.0 V, both of flexible and rigid ECDs based on DNPV and Bn-NPV exhibited reversible color change from purple to deep purple and red to deep viologen respectively, while ECDs based on DAcPV and Bn-AcPV exhibited a color change from yellow to black and pale yellow to green under applied voltage of 1.2 V, respectively. After 1000 cycles, flexible and rigid ECDs showed good stability. Especially, the flexible ECDs maintained good performance after 1000 bending cycles. In additional, the ECDs based on these viologen derivatives were prepared to displayer, which showed clear display function. And ECDs driven by solar cells demonstrated good stability after 100 cycles. Furthermore, it showed that the rigid ECD based on DAcPV with high solar irradiation modulation of 70.3 %, holds great potential in smart window applications.

Facile, low-cost and scalable preparation of V2O5/PEDOT:PSS inks for solution-processed multicolor electrochromic films

Poly(3,4-ethylenedioxythiophene) doped with poly(styrene sulfonic acid) (PEDOT:PSS) is extensively used as a commercial ink for electrochromic coatings. However, PEDOT:PSS film has the defect of a single color change, which limits the wide range of applications. The development of hybrid electrochromic inks containing PEDOT:PSS has attracted considerable attention attributed to their high electrical conductivity, large optical modulation, excellent cycling stability and multicolor variation. In this work, the color range of electrochromic PEDOT:PSS ink was adjusted by a simple and low-cost solution blending process method. The solution-processable multicolor vanadium pentoxide (V2O5) nanoribbons synthesized by a facile solution treatment process were used as additives to enlarge the color range of PEDOT:PSS ink. The electrochromic performance of V2O5-PEDOT:PSS hybrid films with V2O5 nanoribbon inclusions ranging from 0 wt% to 100 wt% was systematically studied. Our results demonstrate that the V2O5/PEDOT:PSS hybrid film can combine the color range of mixing inorganic and organic electrochromic materials. The spray-coated hybrid film with 40 % V2O5 nanoribbon (40VPE) shows a reversible multicolor change ranging from navy blue, yellow-green, orange, grey to blue. Moreover, the 40VPE hybrid film also exhibits high optical contrast (50.2 % at 660 nm), rapid response speed (2.7/3.8 s) and excellent cycling stability (sustaining 97 % of initial contrast after 100 cycles). The solution-processable and large-scale V2O5-PEDOT:PSS hybrid inks exhibit promising applications in multicolor electrochromic devices.

High-durability organic electrochromic devices based on in-situ-photocurable electrochromic materials

•Organic electrochromic materials with in situ photocuring features were proposed •The electrochromic film and device showed attractive durability and calendar life •A high-resolution electrochromic photolithographic patterning was demonstrated Electrochromic materials can undergo electrochemically driven redox processes resulting in optical signal changes, and they have shown attractive application potential in smart windows, wearable electronics, electronic papers, etc. However, their research and development (R&D) are still limited due to the lack of suitable materials and processing strategies to achieve high durability. Here, in-situ-photocurable electrochromic molecules were designed and synthesized to overcome the aforementioned challenges. Compared with the existing doping mode and polymerization mode, in-situ-photocured electrochromic films and devices showed superior durability (e.g., adhesion, multi-dimension stability, and full-contrast calendar life of >120 days) and remarkable overall performance (e.g., transparency = ∼90%, optical modulation = 72.7%, and full-contrast cycle life > 21,000). Furthermore, a high-resolution electrochromic photolithography for micro-nano patterning (recognizable pattern size: ∼2 μm, the best electrochromic resolution to date) was successfully achieved. Based on this, some potential applications in multi-level information encryption and tunable secondary colors were demonstrated. Electrochromic materials can undergo electrochemically driven redox processes resulting in optical signal changes, and they have shown attractive application potential in smart windows, wearable electronics, electronic papers, etc. However, their research and development (R&D) are still limited due to the lack of suitable materials and processing strategies to achieve high durability. Here, in-situ-photocurable electrochromic molecules were designed and synthesized to overcome the aforementioned challenges. Compared with the existing doping mode and polymerization mode, in-situ-photocured electrochromic films and devices showed superior durability (e.g., adhesion, multi-dimension stability, and full-contrast calendar life of >120 days) and remarkable overall performance (e.g., transparency = ∼90%, optical modulation = 72.7%, and full-contrast cycle life > 21,000). Furthermore, a high-resolution electrochromic photolithography for micro-nano patterning (recognizable pattern size: ∼2 μm, the best electrochromic resolution to date) was successfully achieved. Based on this, some potential applications in multi-level information encryption and tunable secondary colors were demonstrated.

Effect of Hyper-Cross-Linking on the Electrochromic Device Properties of Cross-Linkable Carbazole–Diphenylamine Derivatives

Triphenylamine derivatives are promising organic electrochromic (EC) materials due to their easy synthesis, low oxidation potentials, high charge-carrier mobilities, electrochemical stability, coloration efficiency, and tunability of EC properties via substitution. Further, the cross-linking strategy provides an added advantage to the small-molecule-based EC devices in terms of better-quality EC films with enhanced EC properties. Herein, we discuss the EC properties of two carbazole–diphenylamine derivatives, C-Sty2 and C-Sty3, with two and three thermally cross-linkable styryl units, respectively, following a donor−π–donor (D−π–D) design, where both the carbazole moiety and cross-linking styrene groups modulate the photophysical and EC properties. Both styryl derivatives formed rigid, uniform, and transparent films with high solvent resistance and exhibited excellent thermal and electrochemical stability upon cross-linking. C-Sty3, with three cross-linkable styryl units, could form more extended cross-links, leading to hyper-cross-linked films with distinct, regular, and porous morphology compared to C-Sty2. Spectroelectrochemical studies of the films showed a color change from a transparent colorless state to an initial light-yellow color and then a final dark-blue color with a color contrast of 65% at 890 nm for C-Sty2 and 78% at 850 nm for C-Sty3. The hyper-cross-linked films of C-Sty3 demonstrated enhanced coloration efficiency (248 cm2/C), optical contrast, and open-circuit memory compared to C-Sty2. Electrochemical impedance spectroscopy analysis showed lower solution and charge-transfer resistances (Rs and Rct, respectively) for hyper-cross-linked films of C-Sty3, indicating higher conductivity and ion diffusion compared to C-Sty2. Thus, a comparison of the EC properties of two polymers with the same electroactive groups reveals the significance of hyper-cross-linking in the EC properties of these cross-linked polymers. Furthermore, the EC properties of the hyper-cross-linked D−π–D derivative, C-Sty3, were compared to those of previously reported molecules, demonstrating the importance of highly branched conducting polymers for EC applications.

Organic electrochromic energy storage materials and device design.

While not affecting electrochemical performance of energy storage devices, integrating multi-functional properties such as electrochromic functions into energy storage devices can effectively promote the development of multifunctional devices. Compared with inorganic electrochromic materials, organic materials possess the significant advantages of facile preparation, low cost, and large color contrast. Specifically, most polymer materials show excellent electrochemical properties, which can be widely used in the design and development of energy storage devices. In this article, we focus on the application of organic electrochromic materials in energy storage devices. The working mechanisms, electrochemical performance of different types of organics as well as the shortcomings of organic electrochromic materials in related devices are discussed in detail.

A flexible flame-retardant electrochromic device

Organic electrochromic materials and devices have been developed and successfully applied into smart windows, car anti-glare rearview mirrors, etc. However, the use of highly flammable materials to produce safety hazards is a big issue, which seriously hinders further application. Here, a novel organic electrochromic material with flame-retardant properties has been developed, and the effect of organophosphorus flame retardant in electrochromic property and flame retardant feature of the device were investigated systematically. More importantly, the device has good overall performance——reversibility (>20000 cycles), coloration efficiency (155 cm2/C), and transmittance change (66.6%). This promising flame-retardant electrochromic material will promote the development of organic ECDs in smart displays, electronic products, and camouflage.

Conquering residual light absorption in the transmissive states of organic electrochromic materials.

In this short review, we provide an overview of our efforts in developing a family of anodically coloring electrochromic (EC) molecules that are fully transparent and colorless in the charge neutral state, and that can rapidly switch to a vibrantly colored state upon oxidation. We employ molecules with reduced conjugation lengths to center the neutral state absorption of the electrochrome in the ultraviolet, as desired for highly transparent and colorless materials. Oxidation creates radical cations that absorb light in the visible and near infrared regions of the electromagnetic spectrum, thus providing a host of accessible colors. Combining a density functional theory (DFT) computational approach fed back to the synthetic effort, target molecules are proposed, synthesized and studied, directing us to develop a complete color palette based on these high contrast ACE molecules. Utilizing pendant phosphonic acid binding substituents in concert with high surface area mesoporous indium tin oxide (ITO) electrodes, the electrochromes can be distributed throughout the oxide film, bringing high extent of light absorption and color density.

Electropolymerization, spectroelectrochemistry and electrochromic properties of cross-conjugated and conjugated selenophenothiophenes with thiophene bridge

Two novel selenophenothiophene homopolymers, P(SeT1) and P(SeT2), were electrochemically prepared for the first time from their corresponding monomers (i) conjugated 2,5-di(thiophen-2-yl)selenopheno[3,2-b]thiophene (1) and (ii) cross-conjugated 2,5-di(thiophen-2-yl)selenopheno[2,3-b]thiophene (2) to explore their electrochromic behaviors. The effects of conjugation and cross conjugation on the electrochromic performances and electrochemistry and spectroelectrochemistry of the polymers were systematically studied. While the cross conjugated polymer film of P(SeT2) displayed a color change from yellow to a light green upon oxidation, the conjugated polymer film of P(SeT1) showed an orange color in the neutral and a claret red in the oxidized state. The polymer P(SeT1), owing to its extended π-conjugation, had a lower optical band gap of 1.82 eV, compared to the polymer P(SeT2) (2.27 eV). Their electrochromic performances displayed that P(SeT2) had a higher optical contrast (46.2%) and a lower response time (oxidation time of 1.34 s at 680 nm). The first electrochemically-synthesized poly(selenophenothiophene) films showed good electrochemical activity and electrochromic properties. Moreover, this pioneering study suggests a new strategy for designing and preparing organic electrochromic materials possessing selenophenothiophene units.

A Cathodic Electrochromic Material Based on Thick Perylene Bisimide Film with High Optical Contrast and High Stability

A Cathodic Electrochromic Material Based on Thick Perylene Bisimide Film with High Optical Contrast and High Stability

Towards the design of ideal electrochromic materials with low driving voltage based on phthalate derivatives

Small molecular organic electrochromic materials have gradually attracted the attention from academia. Although ester organic electrochromic materials show unique advantages such as significant color change, wide color adjustment range and low cost, their electrochromic mechanisms are still unclear, keeping their driving voltage and stability issues unsolved. In this article, the absorption spectra of phthalate derivatives under different conditions are calculated with time-dependent density functional theory to understand the influences on the electrochromic properties by the electronic and steric effects. By the increased conjugation and reduced steric hindrance, carbonyl linking group is found capable to enhance the absorption in the visible region and exhibit low driving voltages. Further, a new electrochromic compound is designed to improve the luminous effect and lower the driving voltage.

Electrochromic Polymer Ink Derived from a Sidechain‐Modified EDOT for Electrochromic Devices with Colorless Bright State

AbstractPrintable organic electrochromic materials are the key component of flexible low power and low weight displays and dynamic shading systems. A vast number of more or less well‐performing materials is reported in the literature, but only a very limited number of them have been tested in an industrially‐relevant environment so far. Upscaling requires simplicity of synthesis, overall sustainability, low cost and compatibility with simple and high throughput wet‐chemical deposition techniques, such as slot‐die coating or inkjet printing. In the present paper, an original process is described that enables the controlled oxidative polymerization of a water insoluble, functionalized 3,4‐ethylene dioxythiophene (EDOT) derivative. This process leads to the formation of an ink that consists solely of active polymeric material (no dispersing agents) and has suitable rheological properties for use in roll‐to‐roll slot‐die coating or ink‐jet printing. The straightforward deposition, followed by a simple thermal treatment, directly yields stable and homogeneous thin films with state‐of‐the‐art electrochromic performance.

A novel bis(dihydroxypropyl) viologen-based all-in-one electrochromic device with high cycling stability and coloration efficiency

Electrochromism and related devices have been studied for a few decades from both fundamental and technological point of view. At the present stage, screening electrochromic materials with excellent properties is still an interesting job. In our previous work, we have demonstrated that hydroxyalkyl viologens could exhibit satisfying electrochromic behavior. Further, in this paper, the bis(dihydroxyalkyl) viologen, (1,1‘-bis(2,3-dihydroxypropyl) 4,4‘-bipyridine derivative dichloride, DHPV2+2Cl-, was synthesized and incorporated as an electrochromic chromophore in the all-in-one electrochromic devices (ECDs) on the basis of poly (vinyl butyal) (PVB)-carbonate and poły (vinyl alcohol) (PVA)-borax gel electrolytes, respectively. It was found that DHPV2+ 2Cl- in PVB-based gel ECDs underwent reversible switching between transparent and deep blue hue, whereas the clear color changes from colorlessness to amaranth in PVA-borax-based ones upon the potential ranges from 0 V to −1.0 V. For PVB-based gel ECD, spectroelectrochemical studies demonstrated that it only needs a low coloration voltage down to −0.6 V, and exhibites high coloration efficiency (η) up to 301 cm2/C. The optical contrast of it only reduces by 1% after consecutive operation for 10000 cycles between −1.0 V and 0 V, demonstrating an excellent cycling stability of this kind of device. The ECD based on PVA-borax gel modified with glycerol shows burgundy, and good electrochromic performance. It is interesting to note that a relatively large-area PVB-based gel electrochromic devices up to 168 cm2 was realized, the driving voltage and response time being −1.5 V and 12 s, respectively, for blue-violet coloration state. The advantages of electrochromic properties exhibited by 1,1‘-bis(2,3-dihydroxypropyl) viologen dichloride over those reported can be regarded as a pronounced improvement for organic electrochromic materials, and are expected to set the stage for novel electrochromic devices such as smart window and display applications and so forth.

Novel copolymers based on PEO bridged thiophenes and 3,4-ethylenedioxythiophene: Electrochemical, optical, and electrochromic properties

Polythiophene, one of excellent conducting polymers, has attracted great concern as organic electrochromic materials. The electrochromic properties not only depend on the electron transfer of polymers, but also on the ability of ionic conduction in electrolyte. Hence, we designed a new structure of two thiophenyl monomers linked by polyethylene oxide (PEO) and prepared a new copolymer with 3,4-ethylenedioxythiophene (EDOT), which contributes to the easy deposition of the free-standing films by means of electrochemical copolymerization. PEO is of great importance for improving the electrochemical activity. On the one hand, PEO promotes the formation of crosslinking structure leading to a high-quality film. On the other hand, PEO as a soft segment ameliorates the ion-conducting capacity of polymer resulting in the better coloration efficiency (CE) and shorter response time. The as-synthesized films show excellent electrochemical active and electrochromic properties. This work proposes a new strategy of designing and preparing high-quality organic electrochromic material in the future.

Time-Dependent Density Functional Computations of the Spectrochemical Properties of Dithiolodithiole and Thiophene Electrochromic Systems.

The importance of organic electrochromic materials has grown considerably in recent decades due to their application in smart window, automotive, and aircraft technologies. Theoretical prediction of the optical properties should contribute to their better characterization and help the explanation of the experimental data. By using various exchange–correlation functionals, we show how density functional theory (DFT) and the related time-dependent formulation (TDDFT) are able to correctly reproduce the spectrochemical properties of dithiolodithiole and thiophene organic electrochromic systems.

Long-Term Cyclability of Electrochromic Poly(3-hexyl thiophene) Films Modified by Surfactant-Assisted Graphene Oxide Layers.

Organic electrochromic (EC) materials are generally known to be electrochemically unstable during the ion intercalation/deintercalation process. One effective method to stabilize them is incorporating graphene derivatives in the polymer matrix, thereby creating strong interaction between graphene derivatives and polymer. However, previous studies are limited to specific polymers and bulk-blended systems, such as mixing the polymer with graphene derivatives. In this study, we developed a polymer-graphene derivative complex with the chemical assistance of a surfactant (octadecylamine, ODA). Graphene oxide (GO) was introduced as a protective layer on the electrochromic poly(3-hexyl thiophene) (P3HT) films by the Langmuir-Schaefer method. The deposition of the GO-ODA protective layer with high coverage was confirmed by atomic force microscopy and high-resolution X-ray reflectivity. The strong interactions between GO-ODA and P3HT were examined with UV-vis spectrophotometry and X-ray photoelectron spectroscopy. Electrochemical and electrochromic investigations revealed that the GO-ODA layer greatly improved the long-term cyclability of the P3HT film. These findings imply that the GO-ODA complex can significantly stabilize the EC cycling, due to its strong interaction with the P3HT film.

Recent progress on triphenylamine materials: synthesis, properties, and applications

ABSTRACTTriphenylamine is a propeller-like structural chromophore with a nitrogen atom center. The compound has a large steric hindrance and hyper conjugation electronic effect, which can enhance the stability of the nitrogen atomic radical. Triphenylamine materials also have a high hole mobility due to their unique free radicals nature. In this review, we started with the methods of the synthesis including traditional Ullmann, Suzuki Coupling, Heck, Wittig, Stille, and Sonogashira Reaction synthesis, and also the basic experimental and theoretical methods for the characterization of triphenylamine materials. Then, we discussed the properties of triphenylamine, including the optoelectronics, electroluminescence, and electrochromism. Finally, we reviewed the recent progress in the main applications of triphenylamine materials in the field of organic optoelectronic solar cells, electroluminescence materials, and electrochromic materials. In conclusion, this review of triphenylamine materials is a valuable resource for both theorists and experimentalists who are focus on these exciting compound materials.

(Invited) Organic Based Electrochromic and Thermochromic Materials: Design, Characterization and Integration in Flexible Devices

Electrochromism and thermocromism are amongst the most promising chromogenic phenomena having real technological appeal. In particular, Organic electrochromic materials (OEMs) - the focus of the first part of the talk -offer a low power input and low cost solution for applications like smart windows, electrochromic sunglasses, electrochromic paper and displays. 1-3 Depending on the specific application, suitable OEMs should offer a wide color palette, high electrochromic contrast, fast switching, low cost and high stability. Relevant applications like sunglasses and automotive additionally require that the transmitted light experiences negligible color distortion in both device’s limiting states. The Donor-Acceptor (D-A) polymers concept so far gave best results on this very challenging topic. Indeed, the preparation of copolymers constituted by alternating electron rich and electron poor groups leads to devices having brown and even grey low transmittance states. Such result comes at the expenses of a somewhat limited transmittance in the bleached state (T ≈ 60 %). 2 Multichromophoric polymers (MCPs) represent a viable alternative to the D-A concept. Typical MCPs feature a PEDOT conjugated backbone, side chain functionalized with small molecule electrochromic derivatives acting as contrast enhancers and color tuning additives. 4 The most performing MCP so far reported, a naphthalenediimide containing cross-linked PEDOT, features a transmittance level above 80 % all over the visible region in the bleached state, along with a grey (T < 20 %) colored state. Cycling stability in the excess of 1000 cycles was also demonstrated. 5,6 We will discuss the synthesis and characterization of two new MCPs based upon specifically designed small molecule contrast enhancers pertaining to the class of Weitz electrochromes. The resulting side chain PEDOT polymers are able to reversibly switch between a brown and a colorless state, both of them complying with the performance of photochromic lenses. Figure 1a shows a representative example of an electrochromic devices based on said materials. In the second part of the talk we will focus on a particular use of organic thermochromic materials: Time Temperature Indicators for food safety. The spontaneous spoilage of fresh goods – milk might probably be the best everyday life example – due to inappropriate handling and storage, particularly during long distance delivery, is an acknowledged treat for public health, even more serious than adulteration. As such, there is a relevant technological interest towards the development of simple and low-cost smart labels that can be integrated into packages giving information on their whole thermal history. The current Time Temperature Indicator (TTI) 7-9 devices include two classes: a) Integrated circuits featuring data loggers and radio frequency identification chips, and b) simpler color indicators relying on chemical reactions such as enzymatic reactions. The second class is inexpensive and attractive for the packaging industry. We will show a new class of irreversible thermochromic molecular materials whose chemical transformation from a colorless state to a strongly colored one depends upon temperature, chemical substitution and substrate. The selection of the appropriate active molecule/substrate combination provides sensitivity to different targeted time/temperature regimes. 10 The key process providing the required irreversible color change is connected with the “latent pigment” approach. 11 Figure 1b shows one example of the two limiting states of demonstrator smart labels based upon latent squaraine pigments. Figure 1. a) Bleached (left) and colored (right) limiting states of an electrochromic device having the structure PET-ITO/organic electrochrome/electrolyte polymer membrane /Prussian blue/PET-ITO. b) bottom: comparison between a reference and a smart label based on a thermochromic material after 3 h at 4°C and at 25 °C; top: pictures taken at regular intervals of a TTI based on the molecule shown at 25°C. References. 1. J. Jensen, M. Hösel, A. L. Dyer, and F. C. Krebs, Adv. Funct. Mater., 25, 2073–2090 (2015). 2. P. M. Beaujuge, C. M. Amb, and J. R. Reynolds, Accounts Chem. Res., 43, 1396–1407 (2010). 3. P. M. Beaujuge and J. R. Reynolds, Chem. Rev., 110, 268–320 (2010). 4. L. Beverina, G. A. Pagani, and M. Sassi, Chem. Commun., 5413–5430 (2014). 5. M. Sassi et al., Adv. Funct. Mater., 26, 5240–5246 (2016). 6. M. Sassi et al., Adv. Mater., 24, 2004–2008 (2012). 7. M. Cavallini and M. Melucci, ACS Appl. Mater. Interfaces, 7, 16897–16906 (2015). 8. E. Shimoni, E. M. Anderson, and T. P. Labuza, J Food Science, 66, 1337–1340 (2001). 9. M. Riva, L. Piergiovanni, and A. Schiraldi, Packag. Technol. Sci., 14, 1–9 (2001). 10. D. Galliani et al., Advanced Optical Materials, 3, 1164–1168 (2015). 11. J. Zambounis, Z. Hao, and A. Iqbal, Nature, 388, 131–132 (1997). Figure 1