Electrofluorochromic Devices Research Articles

Biomimetic Exploration and Reflection on Switchable Coordination and Narrow-Band Electrofluorochromic Devices.

Electrofluorochromic (EFC) materials and devices with controllable fluorescence properties show great application potential in advanced anticounterfeiting, information storage and display. However, the low color purity caused by the broad emission spectra and underperforming switching time of the existing EFC materials limit their application. Through biomimetic exploration and the study of reversible electrochemical responsive coordination reactions, boron-nitrogen embedded polyaromatics (B,N-PAHs) with narrow-band emission and high color purity have been successfully integrated into EFC systems, which also help to better understand the role of boron in biological activity. The EFC device achieve good performance containing quenching efficiency greater than 90% within short switching time (ton: 0.6s, toff: 2.4s), and nearly no performance change after 200 cycles test. Three primary color (red, green, and blue) EFC devices are successfully prepared. In addition, new phenomena are obtained and discussed in this biomimetic exploration of related boron reactions. The success and harvest of this exploration are expected to provide new ideas for optimizing properties and broadening applications of EFC materials. Moreover, it may provide ideas and reference significance for further exploring and understanding the function of boron compounds in biological systems.

An electrochemically responsive B–O dynamic bond to switch photoluminescence of boron-nitrogen-doped polyaromatics

Boron-doped polycyclic aromatic hydrocarbons exhibit excellent optical properties, and regulating their photophysical processes is a powerful strategy to understand the luminescence mechanism and develop new materials and applications. Herein, an electrochemically responsive B–O dynamic coordination bond is proposed, and used to regulate the photophysical processes of boron-nitrogen-doped polyaromatic hydrocarbons. The formation of the B–O coordination bond under a suitable voltage is confirmed by experiments and theoretical calculations, and B–O coordination bond can be broken back to the initial state under opposite voltage. The whole process is accompanied by reversible changes in photophysical properties. Further, electrofluorochromic devices are successfully prepared based on the above electrochemically responsive coordination bond. The success and harvest of this exploration are beneficial to understand the luminescence mechanism of boron-nitrogen-doped polyaromatic hydrocarbons, and provide ideas for design of dynamic covalent bonds and broaden material types and applications.

Electrofluorochromic Hydrogels by Oligothiophene-Based Color-Tunable Fluorescent Dye Doping.

Soft electronic materials hold great promise for advancing flexible functional devices. Among the various soft materials available, hydrogels are particularly attractive for soft electronic device development due to their inherent properties, including transparency, shape adaptability through swelling/deswelling, and self-healing capabilities. Transparent hydrogels contribute to the creation of advanced smart devices such as sensors, smart windows, and anticounterfeiting technologies. Poly(vinyl alcohol) hydrogels are used as a platform for creating electrofluorochromic (EFC) devices in combination with oligothiophene-conjugated benzothiazole derivatives (OCBs) as fluorescent emitters. OCBs demonstrated excited-state intramolecular proton transfer (ESIPT) behavior with a large Stokes shift and emission changes responsive to solvent polarity and pH stimuli. Even in the solid state, OCBs exhibited strong fluorescence emission across a wide range of colors from blue to red, making them exceptionally well-suited for EFC device development. Their quantum yields in the powder state were obtained between 2.3% and 19.9%. Through the incorporation of OCBs into a PVA hydrogel (OCB@PVA), we achieved the successful fabrication of flexible EFC devices, including electronic paper and smart panels. When electric potentials (-2.4 and +2.4 V) were applied in OCB@PVA, fluorescence color changes were observed by an electrochemically induced pH change owing to electrohydrolysis of water. These devices demonstrated the potential of OCB@PVA hydrogels in the realm of flexible electronics. They could be used to create innovative and versatile devices with stimuli-responsive fluorescence properties.

Design and synthesis of multi-coloured electrochromic and electrofluorochromic asymmetric materials by adjusting the central potential of the compounds

Carbazole and triphenylamine derivatives have become popular research topics in the field of electrochromism and electrofluorochromic due to their excellent reversible oxidative activity, reversible colour change and reversible fluorescence change during electrochemical processes. Four asymmetric carbazole-triphenylamine derivatives 6a-d were designed and synthesized. Both ultraviolet absorption (UV) spectra and fluorescence emission (PL) spectra changed with the change in voltage applied to all compounds. These compounds were fabricated into electrochromic and electrofluorochromic devices, and these devices exhibited excellent cycling stability (cycling stability remains above 95% after 11000 s), short switching time (1.1 s ∼ 1.6 s), high PL contrast (146 ∼ 172), and high colour contrast (47.2% ∼ 50.6%). All the samples fluoresced off in the oxidised state and exhibited alternating yellow-green characteristics, and fluoresced on in the reduced state while exhibiting a highly transparent and colourless state. The experimental results indicated that these materials are expected to be used for the preparation of wearable devices and transparent displays. The research demonstrated that rich color changes can be achieved by adjusting the electrochemical properties of dual redox centered materials.

Electrofluorochromism based on the valence change of europium complexes in electrochemical devices with Prussian blue as the counter electrode.

The electrofluorochromism of Eu complexes based on the valence change between Eu3+ and Eu2+ is demonstrated in a two-electrode electrochemical device consisting of Prussian blue (PB) as the counter electrode. This study aims to improve the electrofluorochromic (EFC) performance of luminescence switching between Eu3+ and Eu2+ by enhancing the electrochemical reactivity of the EFC device. By introducing a PB film as a counter electrode in a two-electrode device, the redox reaction of Eu3+/2+ is promoted because of charge compensation by the counter PB film. The increase in the reaction charge enables faster changes in the photoluminescence from Eu3+ to Eu2+ and an increase in the blue luminescence intensity from the Eu2+ state. This approach achieves a lowered driving voltage, accelerates the electrochemical redox reaction of the Eu complex, and enhances the reversibility of the valence change of the Eu ion.

Transition metal complexes for electrochromic and electrofluorochromic devices

Abstract This minireview discusses recent advances in transition metal complexes for electrochromic (EC) and electrofluorochromic (EFC) devices. EC and EFC materials can switch their color and photoluminescence, respectively, through electrochemical redox reactions. Transition metal complexes offer promising opportunities due to their molecular design versatility for various optoelectrical properties. The review provides an overview of electrochromism and electrofluorochromism, including performance characterization methods and device fabrication techniques. It highlights EC transition metal complexes that can form thin films suitable for device applications and EFC transition metal complexes that can efficiently tune photoluminescence through electrochemical quenching mechanisms. The review also summarizes advanced functions of EC/EFC transition metal complexes, including large optical contrast, fast response, dual-switching of color and emission, and easy device fabrication, which could lead to low-cost displays. Overall, this review article presents the latest research on transition metal complexes for EC and EFC devices and their potential for practical applications.

Survey of Recent Advances in Molecular Fluorophores, Unconjugated Polymers, and Emerging Functional Materials Designed for Electrofluorochromic Use

In this review, recent advances that exploit the intrinsic emission of organic materials for reversibly modulating their intensity with applied potential are surveyed. Key design strategies that have been adopted during the past five years for developing such electrofluorochromic materials are presented, focusing on molecular fluorophores that are coupled with redox-active moieties, intrinsically electroactive molecular fluorophores, and unconjugated emissive organic polymers. The structural effects, main challenges, and strides toward addressing the limitations of emerging fluorescent materials that are electrochemically responsive are surveyed, along with how these can be adapted for their use in electrofluorochromic devices.

Benzochalcodiazole-based donor-acceptor-donor non-symmetric small molecules as dual-functioning electrochromic and electrofluorochromic materials

Bifunctional fluorescent donor-π-acceptor-donor molecules based on the benzoxadiazole (1) or benzothiadiazole (2) have been synthesized and characterized and the effect of chalcogen atom (oxygen vs. sulfur) was investigated. Both dyes exhibited dependence of both emission maxima and fluorescence quantum yield on the solvent polarity. The dyes were found to undergo an electropolymerization reaction when an electrochemical process was carried out in dichloromethane-based electrolyte and no electropolymerization was observed when propylene carbonate-based electrolyte was used. In the propylene-carbonate based electrolyte the fluorophores could be reversibly oxidized with the distinct color change from orange to green in case of 1 and yellow to green for compound 2 and the fluorescence was found to be quenched after electrooxidation. Both color change and quenching of luminescence were found to be reversible. The visible color, strong luminescence in the solid state and electroactivity of the dyes were ideal properties for dual electrochromic and electrofluorochromic applications. The constructed dual-functioning electrochromic and electrofluorochromic device could operate for upwards of 6 h in electrochromic mode, and upwards of 100 min in electrofluorochromic mode. The polymers obtained via electropolymerization were found to exhibit different properties in comparison to monomers.

Reversible vis-NIR electrochromic/electrofluorochromic switching in dual-functional devices modulated by different benzothiadiazole-arylamine anodic components

Herein we show all-in-one electrochromic and electrofluorochromic devices where the ethyl viologen cathode is coupled to different arylamine-BT-arylamine anodes, by which modulation of light absorption and emission in the vis-NIR range is achieved.

Panchromatic Fluorescence Emission from Thienosquaraines Dyes: White Light Electrofluorochromic Devices.

Electrofluorochromic devices (EFCDs) that allow the modulation of the light emitted by electroactive fluorophores are very attractive in the research field of optoelectronics. Here, the electrofluorochromic behaviour of a series of squaraine dyes was studied for the first time. In solutions, all compounds are photoluminescent with maxima located in the range 665–690 nm, characterized by quantum yields ranging from 30% to 4.1%. Squaraines were incorporated in a polymer gel used as an active layer in all-in-one gel switchable EFCDs. An aggregation induced quenching occurs in the gel phase, causing a significant decrease in the emission quantum yield in the device. However, the squaraines containing the thieno groups (thienosquaraines, TSQs) show a panchromatic emission and their electrofluorochromism allows the tuning of the fluorescence intensity from 500 nm to the near infrared. Indeed, the application of a potential difference to the device induces a reversible quenching of their emission that is significantly higher and occurs at shorter switching times for TSQs-based devices compared to the reference squaraine dye (DIBSQ). Interestingly, the TSQs fluorescence spectral profile becomes more structured under voltage, and this could be explained by the shift of the aggregates/monomer equilibrium toward the monomeric species, due to electrochemical oxidation, which causes the disassembling of aggregates. This effect may be used to modulate the colour of the fluorescence light emitted by a device and paves the way for conceiving new electrofluorochromic materials based on this mechanism.

Novel electrofluorochromic materials based on asymmetric D-A-D′ type indolocarbazole-imidazole-triarylamine derivatives

Five indolocarbazole-imidazole-triphenylamine derivatives (5a-e) were designed and synthesized as novel D-A-D′ asymmetric type electrofluorochromic (EFC) materials. Their thermal properties, photophysical properties and electrochemical properties were studied. Five compounds could form uniform amorphous films due to good thermal stability. All compounds exhibited reversible redox-active and EFC characteristics, both the ultraviolet absorption (UV) spectra and the photoluminescence (PL) spectra changed with the change of voltage applied. Intramolecular charge transfer (ICT) characteristics made the compounds more sensitive response to voltage applied. Finally, the EFC devices of five compounds were successfully fabricated, the CV curves of 300 cycles were used to test the stability of the devices. Five devices displayed blue fluorescent switching characteristics and showed different electrochemical behaviors under different voltage applied. Among them, the device of the compound 5e with –OCH3 exhibited the most stable device performance. The asymmetric D-A-D′ type small molecules with the redox-active can provide the feasibility for realizing multifunctional EFC devices.

Stimuli-Induced Reversible Proton Transfer for Stimuli-Responsive Materials and Devices.

ConspectusStimuli-responsive materials have a great potential in various novel photoelectric devices, such as self-adaptive adjustment devices, intelligent detection, molecular computers with information storage capability, camouflage and anticounterfeiting display, various energy-saving displays, and others. However, progress in related areas has been relatively slow because of the lack of high-performance smart materials and the limitations of available reaction mechanisms currently. To address these problems fundamentally, new mechanisms need to be designed and developed, and learning from nature is an effective and intelligent method to achieve this long-awaited target, such as mimicking of proton transfer processes in nature at the molecular/supramolecular level. The stimuli-induced reversible proton transfer system is composed of materials that release or capture protons in response to stimuli and switch molecules that control color and/or fluorescence modulation by protons, and it is applied in stimuli-responsive materials and devices, including bistable electronic/electrochromic devices, electrofluorochromic devices, water-jet rewritable paper, visible-light-responsive rewritable paper, and mechanochromic materials.To help researchers gain deep insight into stimuli-induced reversible proton transfer, we attempted to summarize its reaction mechanism and design principle, and discuss strategies to design and prepare various related stimuli-responsive materials and devices. This Account discusses the different systems in which a color/fluorescence change is induced by the proton transfer process under various stimuli, including electric field, water, light, heat, and stress. Relative very promising applications as well as their performance especially for energy-saving and environmentally friendly devices are then summarized, such as energy-saving bistable electrochromic devices, water-jet rewritable paper, and visible-light-responsive rewritable paper. Meanwhile, we focus on the key influence factors and useful additives for improving the device's performance. At last, challenges and bottlenecks faced by stimuli-responsive materials and devices based on the mechanism of reversible proton transfer are proposed. Moreover, we put forward some suggestions on solving these limitations.These exciting results reveal that smart materials based on the mechanism of proton transfer are extremely attractive and possess great potential in the next generation of energy and resource saving and environmental protection display. We hope that this Account further prospers the field of intelligent stimuli-responsive discoloration materials and next-generation green displays.

Electrofluorochromic Device Based on a Redox-Active Europium(III) Complex

Electrofluorochromism owing to redox reactions on the center europium (Eu) ion in ionic liquids is examined for the helicate complexes (abbreviated as EuL) with a hexadentate pyridine derivative. Typical electrofluorochromism requires extra electroactive units complementing intra- or intermolecular energy transfer to quench fluorophores. Herein, an unprecedentedly simplified electrofluorochromic system overcoming such issues is demonstrated by utilizing reversible electrochemistry of EuL between Eu3+ and Eu2+, which accompanies large emission transition. A three-electrode electrochemical switching device is facilely prepared with an ionic liquid [BMIM][PF6] and EuL mixture. Benefiting from the stable helical coordinated structure of the ligand in [BMIM][PF6], highly enhanced red fluorescence of EuL with small quantity (≤1 wt %) is utilized. Rapid response and large contrast of luminescence are achieved: the emission is drastically quenched at the reduced state (Eu2+) and it is successfully restored by subsequent oxidation (Eu3+). The reversible fluctuation of excitation and emission spectra of an electrofluorochromic device is achieved in the potential window within ±2 V. The device affords excellent optoelectric properties in terms of well-controlled luminescence switching depending on the applied potentials and its durability. This work paves an efficient and smart way toward Eu luminescence control in optoelectronic devices.

Overview on the Recent Progress on Electrofluorochromic Materials and Devices: A Critical Synopsis

AbstractThe phenomenon of electrofluorochromism occurs whenever the fluorescence of a material can be reversibly modulated, both in terms of intensity and color change, through the application of an electrical stimulus. Electrofluorochromic (EFC) materials have gained a great interest in the last decade, since they offer access to the development of different optoelectronic devices. Great efforts have been made to achieve highly performing EFC materials either as small organic molecules or as polymers. A critical overview of the most recent materials progress development is presented here, trying to guide the reader toward the most remarkable advancements in this field in the last years. This synoptic frame is completed by the recognition of the weak progress done on the development of the related EFC devices, which cannot be achieved without the identification of the most interesting applications. Among the many issues that are still open, it is necessary to correctly define the performance metrics for a suitable characterization of EFC materials and devices. Indeed, most of the published data are not homogeneous and the lack of standardized procedures really hampers a performance comparison among the various systems. Thus, standardized procedures are desirable and would allow for an easier transfer of this technology.

A Single-Pixel RGB Device in a Colorful Alphanumeric Electrofluorochromic Display.

With the rapid development of human society, consumer electronics have brought marvelous changes to human daily life, but they are accompanied by the much higher demand of display quality and visual experience. Therefore, ideal conversion among the three primary colors-red (R), green (G), and blue (B)-in a single pixel has been a better way to avoid the insurmountable technical barrier of subpixel technology of modern displays. Electrofluorochromic (EFC) materials capable of a novel luminescent switching, open a powerful way to design optoelectronic devices for displays and information storage etc. Colorful EFC devices, especially emitting the ideal three primary colors without subpixel technology, have been a challenge for years. Herein, a long-awaited single-pixel device with RGB color is fabricated successfully based on proton-coupled electron transfer. The RGB EFC device exhibits outstanding EFC properties, such as low turn-on voltage (+1.0 and -1.0 V), large color gamut, and good stability (500 cycles for each color). Prototypes of colorful alphanumeric displays are well demonstrated in a facile way. The success of this new exploration of single-pixel RGB EFC device not only provides the possibility of full-color emission in EFC devices, but also will widely broaden the EFC system and their applications.

Highly Reversible Electrofluorochromism from Electrochemically Decoupled but Electronically Coupled Molecular Dyads

AbstractAlthough electrofluorochromism enables unique optoelectronic applications, its utility has been limited by poor reversibility. It is demonstrated that high reversibility in electrofluorochromism is obtainable from molecular dyads having a redox‐stable acceptor and an aromatic or antiaromatic donor. The structural control aims to generate excited‐state conjugation that produces twisted intramolecular charge‐transfer fluorescence, while suppressing the ground‐state conjugation in order to confine electrochemical processes exclusively within the acceptor unit. Overpotential‐free electrofluorochromism can be achieved with a high fatigue resistance against repeated electrochemical cycles. The electrofluorochromism is investigated using structural, spectroscopic, electrochemical, spectroelectrochemical, and quantum chemical techniques. The studies reveal that electrochemical gating of intramolecular charge transfer is the key mechanism underlying the improved electrofluorochromism performance. The study will provide novel insights into the future development and applications of electrofluorochromic devices.

Synthesis and Characterization of Novel Triarylamine Derivatives with Dimethylamino Substituents for Application in Optoelectronic Devices.

Two novel triphenylamine-based derivatives with dimethylamino substituents, N, N'-bis(4-dimethylaminophenyl)- N, N'-bis(4-methoxyphenyl)-1,4-phenylenediamine (NTPPA) and N, N'-bis(4-dimethylaminophenyl)- N, N'-bis(4-methoxyphenyl)-1,1'-biphenyl-4,4'-diamine (NTPB), were readily prepared for investigating the optical and electrochromic behaviors. These two obtained materials were introduced into electrochromic devices accompanied with heptyl viologen (HV), and the devices demonstrate a high average coloration efficiency of 287 cm2/C and electrochemical stability. Besides, NTPB/HV was further used to fabricate electrofluorochromic devices with a gel type electrolyte, and exhibit a controllable and high photoluminescence contrast ratio ( Ioff/ Ion) of 32.12 from strong emission to truly dark by tuning the applied potential in addition to a short switching time of 4.9 s and high reversibility of 99% after 500 cycles.

Lighting with organophosphorus materials: solution-processed blue/cyan light-emitting devices based on phosphaphenalenes.

A family of electroluminescent organophosphorus materials for solution-processed organic light-emitting diodes is reported. The investigated systems present a six-membered phosphorus heterocycle fused with a pyrrole or benzopyrrole moiety. The materials exhibit high thermal stability and are soluble in a variety of organic solvents. Already in very simple OLED architectures, the novel electroluminescent materials display blue or cyan luminescence; i.e. color coordinates x = 0.18; y = 0.21 and x = 0.22; y = 0.30, respectively, with performances that are in the range of state-of-the-art phosphazene materials. In electrofluorochromic devices, the color emission coordinates of the organophosphorus materials are tuned upon applying an electric potential. These findings set the bedrock for the development of new generations of organophosphorus light-emitting devices.

Fluorescent gels: a review of synthesis, properties, applications and challenges

Soft material gels are important biomaterials for tissue engineering and biomedicine. Fluorescent gels possess the additional property of being light emitting, with advanced applications in sensing, bioimaging, and electrofluorochromic devices.

Reversible self-powered fluorescent electrochromic windows driven by perovskite solar cells.

Self-powered electrofluorochromic devices (EFCDs) have attracted particular attention for smart windows of green buildings. In this work, we report a perovskite solar cell (PSC) driven self-powered EFCD. For the first time, electrochromic material polyoxometalates (POMs) and a fluorescent component are made into wet adhesives. A special design feature is that POMs and magnesium composed a battery powering the EFCD bleaching, and the device can be quickly coloured after connecting with the PSCs by the electrical power generated through solar energy conversion. Therefore, without any additional external bias, the fabricated EFCD undergoes an electrochromic transition from white semitransparent to dark blue-tinted, and under UV it presents reversible fluorescence switching between yellow and dark.