AIEE-Active and Electrochromic Bifunctional Polymer and a Device Composed thereof Synchronously Achieve Electrochemical Fluorescence Switching and Electrochromic Switching

Aggregation-induced emission (AIE): emerging technology based on aggregate science

Functional materials serve as the basic elements for the evolution of technology. Aggregation-induced emission (AIE), as one of the top 10 emerging technologies in chemistry, is a scientific concept coined by Tang, et al. in 2001 and refers to a photophysical phenomenon with enhanced emission at the aggregate level compared to molecular states. AIE-active materials generally present new properties and performance that are absent in the molecular state, providing endless possibilities for the development of technological applications. Tremendous achievements based on AIE research have been made in theoretical exploration, material development and practical applications. In this review, AIE-active materials with triggered luminescence of circularly polarized luminescence, aggregation-induced delayed fluorescence, room-temperature phosphorescence, and clusterization-triggered emission at the aggregate level are introduced. Moreover, high-tech applications in optoelectronic devices, responsive systems, sensing and monitoring, and imaging and therapy are briefly summarized and discussed. It is expected that this review will serve as a source of inspiration for innovation in AIE research and aggregate science.

Simultaneously achieving high capacity storage and multilevel anti-counterfeiting using electrochromic and electrofluorochromic dual-functional AIE polymers

With the advent of the big data era, information storage and security are becoming increasingly important. However, high capacity information storage and multilevel anti-counterfeiting are typically difficult to achieve simultaneously. To address this challenge, herein, two electrochromic and electrofluorochromic dual-functional polymers with aggregation-induced emission (AIE) characteristics were rationally designed and facilely prepared. Upon applying voltages, the absorption and fluorescence spectra of the AIE polymers can undergo reversible changes, accompanied by variation of their color and emission. By utilizing the controllable characteristics of the polymers, dual-mode display devices were fabricated via a simple spraying technique. More interestingly, a four-dimensional color code device was constructed by adding color change multiplexing to the two-dimensional space, thereby achieving high capacity information storage. Moreover, the color code device can also be applied in the multilevel anti-counterfeiting area. The encrypted information can be dynamically converted under different voltages. Thus, the AIE polymers show great promise for applications in multidimensional information storage and dynamic anti-counterfeiting, and the design strategy may provide a new avenue for advanced information storage and high security technology.

Deciphering the Dynamics of Organic Nanoaggregates with AIEE Effect and Excited States: Lipophilic Benzothiadiazole Derivatives as Selective Cell Imaging Probes

An aggregation-induced emission enhancement (AIEE) effect in fluorescent lipophilic 2,1,3-benzothiadiazole (BTD) derivatives and their organic nanoaggregates were studied. A set of techniques such as single-crystal X-ray, dynamic light scattering (DLS), electron paramagnetic resonance (EPR), UV-vis, fluorescence, and density functional theory (DFT) calculations have been used to decipher the formation/break (kinetics), properties, and dynamics of the organic nanoaggregates of three BTD small organic molecules. An in-depth study of the excited-state also revealed the preferential relaxation emissive pathways for the BTD derivatives and the dynamics associated with it. The results described herein, for the first time, explain the formation of fluorescent BTD nanoaggregate derivatives and allow for the understanding of their dynamics in solution as well as the ruling forces of both aggregation and break processes along with the involved equilibrium. One of the developed dyes could be used at a nanomolar concentration to selectively stain lipid droplets emitting an intense and bright fluorescence at the red channel. The other two BTDs could also stain lipid droplets at very low concentrations and were visualized preferentially at the blue channel.

Multiresponsive Fluorescence "Turn ON-OFF" Switch on PB@EuW10/SiO2 Composite for Dual Spectral Detection of N2H4 and H2O2

Herein, a fluorescence "turn ON-OFF" switch model PB@EuW₁₀/SiO₂ core@shell composite is designed and fabricated by coating EuW₁₀-containing silica layer on Prussian blue (PB) nanoparticles via a facile method. It is found that the presence of PB can quench the photoluminescence of the composite which arises from EuW₁₀. When hydrazine is mixed with the composite dispersion, PB can be reduced to Prussian white (PW), resulting in the decrease of UV absorption and the appearance of photoluminescence (turn ON). In addition, PW can also be converted back to PB, which is achieved by adding hydrogen peroxide, and the photoluminescence of the composite is quenched again (turn OFF). Thus, the composite is applied for N₂H₄ and H₂O₂ detection by fluorescence spectroscopy and UV-vis absorption spectroscopy. Wide linear ranges for N₂H₄ and H₂O₂ detection with low detection limits are found for both detection methods on the PB@EuW₁₀/SiO₂ core@shell composite. Besides, the color from light blue to colorless of the detection dispersion can also indicate the turn ON-OFF switch for fluorescence. Furthermore, the proposed model can also be extended to other composites.

Electroluminochromic Materials: From Molecules to Polymers

Electroluminochromism is an interesting property found in certain classes of molecules and polymers whose photoluminescence can be modulated through the application of an external electrical bias. Unlike electrochromic materials, electroluminochromic counterparts and their applications are comparatively fewer in quantity and are less established. Nonetheless, there prevails an increasing interest in this class of electro-active materials due to their potential applications in optoelectronics, such as smart-displays, and chemical and biological sensing. This review seeks to showcase the different classes of electroluminochromic materials with focus on (i) organic molecules, (ii) transition metal complexes, and (iii) organic polymers. The mechanisms and electroluminochromic performance of these classes of materials are summarized. This review should allow scientists to have a better and deeper understanding of materials design strategies and, more importantly, structure-property relationships and, thus, develops electroluminochromic materials with desired performance in the future.

AIE-Active Polyamide Containing Diphenylamine-TPE Moiety with Superior Electrofluorochromic Performance

Electrofluorochromism has attracted great attention due to the intelligence optoelectronic and sensing applications. The intrinsically switchable fluorophores with high solid-state fluorescence are regarded as key for ideal electrofluorochromic materials. Here, we reported an AIE-active polyamide with diphenylamine and tetraphenylethylene units, showing high fluorescence quantum yield up to 69.1% for the solid polymer film and stable electrochemical cycling stability. The polyamide exhibited reversible color and emission switching even in hundreds of cycles, and the fluorescence on/off contrast ratio was determined up to 417, which is the highest value to our knowledge. Furthermore, as the response time is vital for the real-life applications, to speed up the response of electrofluorochromism, a porous polymer film was readily prepared through a facile method, notably exhibiting high fluorescence contrast, long-term stability and obviously improved response, due to the sharply increased surface area. Therefore, the AIE-functionalization combining the porous structure strategy will synergistically and dramatically improve the electrofluorochromic performance, which will also promote their practical applications in the near future.

Multi-color electrochromism containing green color based on electrochemically polymerized star-shaped phenyl bithiophene

The pure thiophene-based polymer pPHBT was obtained to exhibit multi-color electrochromic switching with a surprising green electrochromic color.

Controllable Electrochromic Polyamide Film and Device Produced by Facile Ultrasonic Spray-coating

Thermally stable TPA-OMe polyamide films with high transmittance modulation in response to applied potential are formed by facile ultrasonic spray-coating. Four processing conditions (Film A, Film B, Film C and Film D) through tuning both solution concentrations and deposition temperatures can be utilized for the formation of wet and dry deposited films with two film thickness intervals. The electrochromic results show that the dry deposited rough films at higher deposition temperature generally reveal a faster electrochromic response, lower charge requirements (Q) and less conspicuous color changes (smaller optical density change (ΔOD) and lightness change (ΔL*)) during the oxidation process as compared to the wet deposited smooth films at lower deposition temperature. Moreover, thicker electrochromic films from increased solution concentration exhibit more obvious changes between coloration and bleaching transition. All these four polyamide films display colorless-to-turquoise electrochromic switching with good redox stability. The large scale patterned electrochromic film and its application for assembled device (10 × 10 cm² in size) are also produced and reversibly operated for color changes. These represent a major solution-processing technique produced by ultrasonic spray-coating method towards scalable and cost-effective production, allowing more freedoms to facilitate the designed electrochromic devices as required.

Two intensified fluorescence colors' switching achieved by branched dye nanoaggregates

In this study, a variety of branched target dyes containing double internal proton transfer segments were synthesized. For comparison, some linear analogs including a single internal proton transfer part were synthesized. The corresponding reference molecules lacking proton transfer segments were also prepared. The properties and aggregation modes of these dye aggregates were investigated on the basis of scanning electron microscopy images, transmission electron microscopy images, dynamic light scattering, X-ray diffraction, UV/visible absorption spectra and fluorescence emission spectra. The results showed that molecular aggregates with the morphologies of nano-scaled rounded or cubic particles of the target branched dyes could be yielded in mixed organic solvent/H₂O solution. A remarkable emission enhancement and fluorescence switching process (from bright yellow to luminous pure blue) under 365 nm lamp irradiation was observed for these target branched dye nanoaggregates. However, no aggregates of the reference branched dyes free of hydroxyl groups were formed and no obvious spectral variations were found. In contrast, all the studied linear dyes yielded molecular nanoaggregates in mixed organic solvent/H₂O solution, and only intensified single normal blue fluorescence emission was presented. This study provided real examples of some branched organic dye aggregates which were capable of displaying naked-eye enhanced fluorescence color switching under an UV lamp.

Visible-to-NIR Electrochromic Device Prepared from a Thermally Polymerizable Electroactive Organic Monomer

A monomer (1) consisting of a benzothiadiazole core flanked by two triphenylamines and two styrene pendant moieties was prepared. The monomer was fluorescent with its emission spanning 145 nm in the visible, contingent on the organic solvent used for the measurement. In addition to its positive solvatochromism, the absolute fluorescence quantum yield (Φ_fl) was consistently >20% with values >80% being measured in hexane, toluene, diethyl ether, and toluene. 1 could be reversibly oxidized with an oxidation potential of 880 mV vs SCE. The monomer could be immobilized on ITO-coated glass substrates. The resulting 425 nm thick immobilized film (poly-1) was 15% thinner than the monomer coating deposited by spray- and spin-coating. The electroactive film did not delaminate from the electrode upon either washing or cycling electrochemically between its oxidized and neutral states. Its absorption at 460 nm bleached upon electrochemical oxidation with the formation of a strong absorption at 880 nm and in the NIR, similar to 1. The perceived reversible color change with applied potential switched between yellow and gray. The fluorescence intensity of poly-1 could be switched with applied potentials. A passive transmissive device prepared from poly-1 was both electrochromic and fluorochromic, exhibiting reversible color change and fluorescence quenching.

Electrothermally Driven Fluorescence Switching by Liquid Crystal Elastomers Based On Dimensional Photonic Crystals

In this article, the fabrication of an active organic-inorganic one-dimensional photonic crystal structure to offer electrothermal fluorescence switching is described. The film is obtained by spin-coating of liquid crystal elastomers (LCEs) and TiO₂ nanoparticles alternatively. By utilizing the property of LCEs that can change their size and shape reversibly under external thermal stimulations, the λ_max of the photonic band gap of these films is tuned by voltage through electrothermal conversion. The shifted photonic band gap further changes the matching degree between the photonic band gap of the film and the emission spectrum of organic dye mounting on the film. With rhodamine B as an example, the enhancement factor of its fluorescence emission is controlled by varying the matching degree. Thus, the fluorescence intensity is actively switched by voltage applied on the system, in a fast, adjustable, and reversible manner. The control chain of using the electrothermal stimulus to adjust fluorescence intensity via controlling the photonic band gap is proved by a scanning electron microscope (SEM) and UV-vis reflectance. This mechanism also corresponded to the results from the finite-difference time-domain (FDTD) simulation. The comprehensive usage of photonic crystals and liquid crystal elastomers opened a new possibility for active optical devices.

Synthesis and optical and electrochemical properties of water-soluble cationic fluorophores based on bispyridinium and dibenzothiophene-S,S-dioxide

Two water-soluble cationic fluorophores (FSOPyCl and FSOmiCl) based on bispyridinium and dibenzothiophene-S,S-dioxide show deep blue emission, and exhibit high photoluminescence quantum yields of 69% and 50% in water, respectively.

Yellow electrochromic polymer materials with fine tuning electrofluorescences by adjusting steric hindrance of side chains

A series of novel conducting conjugated yellow-to-transmissive electrochromic (EC) polymers were designed to research their structure–property relationships, achieving electrofluorescent (EF) switching with applied external potential.

Influence of side chain characteristics on the aggregation-induced emission (AIE) properties of tetrasubstituted tetraphenylethylene (TPE)

The side-chain in TPE derivatives has strong influence in their aggregation induced emission.

Reversal aggregation-induced circular dichroism from axial chirality transfer via self-assembled helical nanowires

Two chiral binaphthyl-based enantiomers, (R/S)-7, can produce gradual reversal AICD signals from solution to aggregation, which can be attributed to axial chirality transfer to self-assembled helical nanowires in aggregation state.

Multichromic Polymers Containing Alternating Bi(3-Methoxythiophene) and Triphenylamine Based Units with Para-Protective Substituents

Two novel triphenylamine-based thiophene derivative monomers, 4-cyano-4′,4″-di(4-methoxythiophen-2-yl)triphenylamine and 4-methoxy-4′,4″-di(4-methoxythiophen-2-yl)triphenylamine, were successfully synthesized. The corresponding polymers including poly (4-cyano-4′,4″-di(4-methoxythiophen-2-yl)triphenylamine) and poly (4-methoxy-4′,4″-di(4-methoxythiophen-2-yl)triphenylamine) were electrochemically synthesized and characterized by multiple test method. The electrochemical measurements and spectroelectrochemical analyses revealed that both of the two polymers had quasi-reversible redox behavior and multi-electrochromic properties. The two polymer films showed reversible electrochemical oxidation, excellent optical contrasts in NIR region (62% at 1070 nm for the first polymer, and 86% at 1255 nm for the second polymer), satisfactory coloration efficiencies and fast switching times. The research on the application of the as prepared polymer in the fabrication of electrochromic device was also conducted, employing PCMTPA or PMMTPA as the anodically coloring materials.

Rational design of asymmetric red fluorescent probes for live cell imaging with high AIE effects and large two-photon absorption cross sections using tunable terminal groups

In this work, we report the synthesis of a family of donor-acceptor (D-A) π-conjugated aggregation-induced red emission materials (TPABT, DTPABT, TPEBT and DTPEBT) with the same core 2,2-(2,2-diphenylethene-1,1-diyl)dithiophene (DPDT) and different amounts and different strengths of electron-donating terminal moieties. Interestingly, TPABT and TPEBT, which have asymmetric structures, give obviously higher solid fluorescence quantum efficiencies in comparison with those of the corresponding symmetric structures, DTPABT and DTPEBT, respectively. In particular, the thin film of TPEBT exhibited the highest fluorescence quantum efficiency of ca. 38% with the highest αAIE. Moreover, TPEBT and DTPEBT with TPE groups showed two-photon absorption cross-sections of (δ) 1.75 × 103 GM and 1.94 × 103 GM at 780 nm, respectively, which are obviously higher than the other two red fluorescent materials with triphenylamine groups. Then, the one-photon and two-photon fluorescence imaging of MCF-7 breast cancer cells and Hela cells, and cytotoxicity experiments, were carried out with these red fluorescent materials. Intense intracellular red fluorescence was observed for all the molecules using one-photon excitation and for TPABT using two-photon excitation in the cell cytoplasm. Finally, TPEBT is biocompatible and functions well in mouse brain blood vascular visualization. It is indicated that these materials can be used as a specific stain fluorescent probe for live cell imaging.

Vanadium substituted Keggin-type POM-based electrochromic films showing high performance in a Li+-based neutral non-aqueous electrolyte

Vanadium substituted Keggin type POM-based electrochromic films show high performance in LiClO₄-based non-aqueous electrolyte. The use of the neutral non-aqueous electrolyte makes it easy to fabricate a device.

Ruthenium-tris(bipyridine) complexes with multiple redox-active amine substituents: tuning of spin density distribution and deep-red to NIR electrochromism and electrofluorochromism

Deep-red to NIR electrochromism and electrofluorochromism are demonstrated with ruthenium-tris(bipyridine) complexes with multiple amine substituents.