Avoiding Photocyclized Degradation of Electrochromic Materials Based on Quantum Chemical Molecular Design

Suppressing the photodegradation of organic electronic materials is crucial for their device applications. This study proposes a method to mitigate the photodegradation. With focus on the molecular design of triphenylamine derivatives commonly used in organic electronics, it was demonstrated that spin distributions of the derivatives would be a good quantum descriptor for predicting the photocyclization resistance to not give carbazole derivatives.

Synthesis, photophysics and two-photon absorption of imidazole-centred tripodal chromophores

Tripodal push-pull chromophores with D-(π-A)3 arrangement were synthesized using 1-methyl-2,4,5-triphenyl-1H-imidazole as a central electron donor, and their thermal, electrochemical, photophysical and non-linear optical properties were studied and corroborated with quantum-chemical calculations. Their facile synthesis involved Suzuki-Miyaura and Knoevenagel reactions, allowing the installation of various peripheral electron acceptors such as formyl, cyano, ester, trifluoromethyl and more complex moieties such as malonic/acetic acid derivatives, indan-1,3-dione and rhodanine. All phenyl rings appended at the central imidazole core were more or less twisted depending on the peripheral substitution. Although imidazole undergoes reversible one-electron oxidation, peripheral acceptors are reduced irreversibly in a multi-electron process. This behaviour is further seen as a variation of the LUMO, while the HOMO remained almost unaltered across the whole series. TD-DFT calculations revealed centrifugal charge transfer from the central imidazole to all C2, C4 and C5 branches occupied by the LUMO, LUMO+1 and LUMO+2. The HOMO-LUMO gap is tuneable within the range of 3.55-2.31 eV, while the longest-wavelength absorption/emission maxima were found within the broad range of 304-448/393-612 nm. Although the absorption spectra are solvent-independent, the emission depends strongly on the solvent polarity and the electron-withdrawing power of the peripheral acceptors. Extended chromophores with complex electron acceptors were investigated as two-photon absorbers, revealing relatively good cross-section values of up to 521 GM and a figure-of-merit (ΦF × δ2PA) of around 190 GM.

One-Step Catalyst-Transfer Macrocyclization: Expanding the Chemical Space of Azaparacyclophanes

In this paper, we report on a one-step catalyst-transfer macrocyclization (CTM) reaction, based on the Pd-catalyzed Buchwald-Hartwig cross-coupling reaction, selectively affording only cyclic structures. This route offers a versatile and efficient approach to synthesize aza[1n]paracyclophanes (APCs) featuring diverse functionalities and lumens. The method operates at mild reaction temperatures (40 °C) and short reaction times (∼2 h), delivering excellent isolated yields (>75% macrocycles) and up to 30% of a 6-membered cyclophane, all under nonhigh-dilution concentrations (35-350 mM). Structural insights into APCs reveal variations in product distribution based on different endocyclic substituents, with steric properties of exocyclic substituents having minimal influence on the macrocyclization. Aryl-type endocyclic substituents predominantly yield 6-membered macrocycles, while polycyclic aromatic units such as fluorene and carbazole favor 4-membered species. Experimental and computational studies support a proposed mechanism of ring-walking catalyst transfer that promotes the macrocycle formation. It has been found that the macrocyclization is driven by the formation of cyclic conformers during the oligomerization step favoring an intramolecular C-N bond formation that, depending on the cycle size, hinges on either preorganization effect or kinetic increase of the reductive elimination step or a combination of the two. The CTM process exhibits a "living" behavior, facilitating sequential synthesis of other macrocycles by introducing relevant monomers, thus providing a practical synthetic platform for chemical libraries. Notably, CTM operates both under diluted and concentrated regimes, offering scalability potential, unlike typical macrocyclization reactions usually operating in the 0.1-1 mM range.

Vinylene-linked diketopyrrolopyrrole chromophores for electrochromism

We report a novel series of vinylene-linked DPP compounds (1-5) formed via Knoevenagel condensation of dimethyl DPP (6) with various aromatic aldehydes. Incorporating the vinylene linkage and photo- and electro-active groups offered the distinct advantage of extending π-delocalization, resulting in deep-coloured solids with absorption maxima extending to 620-680 nm and low redox potentials. The DPP-triphenylamine compound (5) showed electrochromism in the near-infrared region. The colour of the solution changed from blue to green, and the absorption from 680 nm to 740 nm, leading to NIR-to-NIR absorption switching. This system exhibits rapid switching, swift response times (1.4 s and 1.2 s), and reversibility in electrochromic behaviour.

Research Progress in Special Engineering Plastic-Based Electrochromic Polymers

SPECPs are electrochromic polymers that contain special engineering plastic structural characteristic groups (SPECPs). Due to their high thermal stability, mechanical properties, and weather resistance, they are also known as high-performance electrochromic polymer (HPEP or HPP). Meanwhile, due to the structural characteristics of their long polymer chains, these materials have natural advantages in the application of flexible electrochromic devices. According to the structure of special engineering plastic groups, SPECPs are divided into five categories: polyamide, polyimide, polyamide imide, polyarylsulfone, and polyarylketone. This article mainly introduces the latest research on SPECPs. The structural design, electrochromic properties, and applications of these materials are also introduced in this article, and the challenges and future development trends of SPECPs are prospected.

Reversible Electrochromic/Electrofluorochromic Dual Switching in Zn(II)-Based Metallo-Supramolecular Polymer Films

The introduction of novel materials with multifunctional chromogenic properties, such as electrochromic/electrofluorochromic (EC/EFC) properties, has recently attracted prospective interest in the development of various optoelectronic devices and smart windows. In this study, a novel Zn(II)-based metallo-supramolecular polymer (polyZn) has been developed as an ON/OFF switchable EFC application with prominent EC behavior. In this regard, the polymeric chain of polyZn was first synthesized by 1:1 complexation in a zigzag manner with Zn(II) ions at the metal center and 4,4'-[bis(2,2':6',2″-terpyridinyl)benzene]triphenylamine (LTPY-TPA) as the redox-active ditopic ligand. The polyZn exhibits excellent solubility in organic solvents and can form a very good uniform thin film on an indium tin oxide/glass substrate by spin-coating. In a neutral state, transparent polyZn exhibits a bright yellow color to the naked eye (absorption at ∼325 nm). The electroactive triphenylamine (TPA) core of LTPA-TPY, however, undergoes reversible single-electron oxidation when a positive bias of +1.6 V vs Ag/Ag+ is applied, generating radical cations (TPA ↔ TPA•+) with a significant drop in transparency (77%). A noticeable chromic shift in the hue of the film from brilliant yellow to green was observed with the appearance of a near-infrared absorption band at ∼897 nm with a tail of 1300-1600 nm. Interestingly, in addition to this EC phenomenon, the fabricated solid-state polyZn film exhibits intense, high-contrast reddish-orange photoluminescence with λem = 650 nm, which is significantly desired as a molecular probe for bioimaging. Both the TPA core and the redox-inactive Zn(II)-terpyridine core emit orange-red photoluminescence in polyZn, which is significantly quenched upon the oxidation of the film and is re-emitted at 0.0 V vs Ag/Ag+. This ON/OFF EFC transition was sustained for several cycles. This study should motivate to design and create distinctive new unique materials with combined EC/EFC behavior for the fabrication of optoelectronic devices by combining a metal-fluorescent core with a redox-active spacer.

TM-Free and TM-Catalyzed Mechanosynthesis of Functional Polymers

Mechanochemically induced methods are commonly used for the depolymerization of polymers, including plastic and agricultural wastes. So far, these methods have rarely been used for polymer synthesis. Compared to conventional polymerization in solutions, mechanochemical polymerization offers numerous advantages such as less or no solvent consumption, the accessibility of novel structures, the inclusion of co-polymers and post-modified polymers, and, most importantly, the avoidance of problems posed by low monomer/oligomer solubility and fast precipitation during polymerization. Consequently, the development of new functional polymers and materials, including those based on mechanochemically synthesized polymers, has drawn much interest, particularly from the perspective of green chemistry. In this review, we tried to highlight the most representative examples of transition-metal (TM)-free and TM-catalyzed mechanosynthesis of some functional polymers, such as semiconductive polymers, porous polymeric materials, sensory materials, materials for photovoltaics, etc.

Synthesis and Characterization of Novel Triphenylamine-Containing Electrochromic Polyimides with Benzimidazole Substituents

Two novel electrochromic aromatic polyimides (named as TPA-BIA-PI and TPA-BIB-PI, respectively) with pendent benzimidazole group were synthesized from 1,2-Diphenyl-N,N'-di-4-aminophenyl-5-amino-benzimidazole and 4-Amino-4'-aminophenyl-4″-1-phenyl-benzimidazolyl-phenyl-aniline with 4,4'-(hexafluoroisopropane) phthalic anhydride (6FDA) via two-step polymerization process, respectively. Then, polyimide films were prepared on ITO-conductive glass by electrostatic spraying, and their electrochromic properties were studied. The results showed that due to the π-π* transitions, the maximum UV-Vis absorption bands of TPA-BIA-PI and TPA-BIB-PI films were located at about 314 nm and 346 nm, respectively. A pair of reversible redox peaks of TPA-BIA-PI and TPA-BIB-PI films that were associated with noticeable color changed from original yellow to dark blue and green were observed in the cyclic voltammetry (CV) test. With increasing voltage, new absorption peaks of TPA-BIA-PI and TPA-BIB-PI films emerged at 755 nm and 762 nm, respectively. The switching/bleaching times of TPA-BIA-PI and TPA-BIB-PI films were 13 s/16 s and 13.9 s/9.5 s, respectively, showing that these polyimides can be used as novel electrochromic materials.

Synthesis and Characterization of Solution-Processible Donor-Acceptor Electrochromic Conjugated Copolymers Based on Quinoxalino[2',3':9,10]phenanthro[4,5-abc]phenazine as the Acceptor Unit

Donor-acceptor (D-A) type conjugated polymers are of high interest in the field of electrochromism. In this study, three novel conjugated copolymers (PBPE-1, PBPE-2 and PBPE-3) based on quinoxalino[2',3':9,10]phenanthro[4,5-abc]phenazine (A) as the acceptor unit and 4,8-bis((2-octyldodecyl)oxy)benzo[1,2-b:4,5-b']dithiophene (D1) and 3,3-didecyl-3,4-dihydro-2H-thieno[3,4-b][1,4]dioxepine (ProDOT-decyl₂, D2) as the donor units with different donor-to-acceptor ratios were successfully synthesized through Stille coupling polymerization. The polymers were then characterized by cyclic voltammetry (CV), fourier transform infrared (FT-IR) spectoscopy, X-ray photoelectron spectroscopy (XPS), spectroelectrochemistry, thermogravimetry (TG), electrochromic switching and colorimetry. Optical band gap values were calculated as 1.99 eV, 2.02 eV and 2.03 eV, respectively. The three copolymers have good solubility, distinct redox peaks, wide absorption spectra, good thermal stabilities, bright color changes and significant electrochromic switching properties. Compared to the other two copolymers, the PBPE-3 film exhibited high coloration efficiency values of 513 cm²·C^-1 at 504 nm and 475 cm²·C^-1 at 1500 nm. The films have the advantage of exhibiting cathodic and anodic coloration.

Interplay Between Hydrogen Bonding and Electron Transfer in Mixed Valence Assemblies of Triarylamine Trisamides

Hydrogen-bonding interactions are assumed to play a critical role in the long-range transport of light or charge recently observed in supramolecular assemblies of C₃ -symmetrical discotic molecules. Herein, the structure of mixed valence assemblies formed by irradiating triarylamine trisamide (TATA) molecules was determined by multifarious techniques under various conditions with the aim of probing the interplay between the hydrogen bonding network and the rate of electron transport in different states (solution, gel, film). Irradiation was performed under initial states that vary by the degree of association of TATA monomers through hydrogen bonds. Firstly, a significant shift of the N-H and C=O stretching frequencies was observed by FTIR upon irradiation thus revealing an overlooked signature of TATA⋅+ species and interacting mixed valence aggregates. Secondly, gels and films both mostly consist of hydrogen-bonded TATA polymers but their EPR spectra recorded at 293 K reveal very different behaviors: localized electrons in the gels versus fully delocalized electrons in the films. Hydrogen bonding thus appears as a necessary but not sufficient condition to get fast electron transfer rates and a packing of the TATA monomers particularly suitable for charge transport is assumed to exist in the solid state. Finally, defects in the hydrogen bonding network are detected upon increasing the number of radical species in the mixed valence assemblies present in the film state without impeding the delocalization of the unpaired electrons. A delicate balance between hydrogen bonds and packing is thus necessary to get supramolecular polarons in mixed valence TATA assemblies.

Polynaphthylimide–Azomethines Containing Triphenylamine or Carbazole Moieties with Tuned Optoelectronic Properties through Molecular Design

Polyazomethines containing electron-donor triphenylamine (TPA) or carbazole (Cbz) and electron-acceptor naphthyl(di)imide were synthesized and investigated with regard to thermal, optical and electronic features, with a focus on their modulation by molecular design. The polycondesation of an imido-based diamine with a Cbz- or TPA-based dialdehyde led to donor-acceptor polymers with good thermostability, up to 318 °C. These displayed good solubility in organic solvents, which enabled easy polymer processability in thin films with different molecular assemblies. The molecular order improved the charge carrier’s mobility, with a direct impact on the bandgap energy. The optical properties studied by UV–Vis absorption and fluorescence experiments showed solvent-dependence, characteristic for donor-acceptor systems. The structural parameters exerted a strong influence on the light-emissive behavior, with the prevalence of intrinsic or intramolecular charge transfer fluorescence contingent on the donor-acceptor strength and polymer geometry. All polymers showed good electroactivity, supporting both electrons and holes transport. The exchange of Cbz with TPA proved to be an efficient tool with which to decrease the bandgap energy, while that of naphthyl(di)imide with bis(naphthylimide) was beneficial for fluorescence enhancement. This study may contribute to a deeper understanding of the physico-chemistry of electronic materials so as to make them more competitive in the newest energy-related or other optoelectronic devices.

Emerging Electrochromic Materials and Devices for Future Displays

With the rapid development of optoelectronic fields, electrochromic (EC) materials and devices have received remarkable attention and have shown attractive potential for use in emerging wearable and portable electronics, electronic papers/billboards, see-through displays, and other new-generation displays, due to the advantages of low power consumption, easy viewing, flexibility, stretchability, etc. Despite continuous progress in related fields, determining how to make electrochromics truly meet the requirements of mature displays (e.g., ideal overall performance) has been a long-term problem. Therefore, the commercialization of relevant high-quality products is still in its infancy. In this review, we will focus on the progress in emerging EC materials and devices for potential displays, including two mainstream EC display prototypes (segmented displays and pixel displays) and their commercial applications. Among these topics, the related materials/devices, EC performance, construction approaches, and processing techniques are comprehensively disscussed and reviewed. We also outline the current barriers with possible solutions and discuss the future of this field.

Investigation on the binary ionization choices for large conjugated amines during electrospray ionization

RATIONALE

Generally, amines form protonated cations ([M + H]⁺ ) in positive polarity during electrospray ionization (ESI). However, it was found that large conjugated amines (LCAs) had binary ionization choices of generating either radical cations (M^•+ ) or [M + H]⁺ during ESI. Investigation on the mechanism would further our understanding of ESI.

METHODS

In this work, the binary ionization behavior of LCAs was reported and studied. Internal factors (functional groups and sizes of conjugated systems) and external factors (solvent type, flow rate, and electrode position) were systematically investigated and discussed.

RESULTS

For the internal factors, electron-donating groups and large conjugated structures of LCAs were conducive to the generation of M^•+ . For the external factors, aprotic solvent, higher flow rate, and shorter distance from the electrode to the spray cone facilitated the formation of M^•+ but hampered the generation of [M + H]⁺ .

CONCLUSION

The present study illustrated that the formations of M^•+ and [M + H]⁺ for LCAs were two independent processes. The M^•+ cations of LCAs were formed on the surface of the electrode through electrochemical oxidation, whereas the [M + H]⁺ cations were generated following the typical ESI evolution process. By regulating the external factors, the ionization results of LCAs could be well modulated.

Photochromic and Electrochromic Hydrogels Based on Ammonium- and Sulfonate-Functionalized Thienoviologen Derivatives

Ammonium cations and sulfonate anions have been introduced as end-caps for alkyl viologens with thiophene-derived bridges. When the as-prepared thienoviologen derivatives are dispersed in polyacrylamide (PAAm) hydrogels, photochromic (PC) and electrochromic (EC) bifunctional hydrogels can be simply realized. The incorporated thiophene or ethylenedioxylthiophene bridge not only expands the photoresponse range but also stabilizes the photoinduced radical intermediate. Therefore, reversible PC and EC behaviors can be achieved for hydrogels containing thienoviologens N,N'-di(3-(trimethylammonio)propyl)-4,4'-(thien-2,5-diyl)bispyridinium tetrabromide (ATV), N,N'-bis(3-sulfonatopropyl)-4,4'-(thien-2,5-diyl)bispyridinium (STV), N,N'-di(3-(trimethylammonio)propyl)-4,4'-(3,4-ethylenedioxylthien-2,5-diyl)bispyridinium tetrabromide (AETV), and N,N'-bis(3-sulfonatopropyl)-4,4'-(3,4-ethylenedioxylthien-2,5-diyl)bispyridinium (SETV). On the contrary, no photochromism can be observed for PAAm hydrogels based on N,N'-di(3-(trimethylammonio)propyl)-4,4'-bipyridinium tetrabromide (AV) and N,N'-bis(3-sulfonatopropyl)-4,4'-bipyridinium (SV) without thiophene bridges. Furthermore, no significant coloration difference can be observed between the hydrogels containing ammonium- and sulfonate-functionalized viologens. However, during repetitive cycles, the transmittance contrast losses of electrochromic devices (ECDs) based on the hydrogels containing ammonium-modified viologens are lower than those for sulfonate-substituted viologens probably due to their larger number of cation-anion pairs and thus higher solubility in aqueous media. Typically, no observable difference can be found for unsealed ECDs after 15 days in ambient conditions. Additionally, a large-area ECD with a diameter of 10 cm has been facilely fabricated by simply sandwiching the EC hydrogels, and the transparency can be finely tuned upon applying different potentials. Overall, our findings may provide a new path to design multifunctional hydrogels with PC and EC responses.

High-Performance Electrochromic Covalent Hybrid Framework Membranes via a Facile One-Pot Synthesis

Porous framework materials have sparked enormous interest in the electrochromic field, as they possess intrinsic high porosity and a large surface area that are beneficial for electron and ion transport. However, the fabrication of these porous framework materials often requires multiple processing steps or harsh reaction conditions, which significantly limit large-scale fabrication of such materials. In this work, we report a one-pot in situ polycondensation method to construct electrochromic covalent hybrid framework membranes via nucleophilic substitutions between hexachlorocyclotriphosphazene (HCCP) and triphenylamine (TPA) in an ambient environment. With the high transparency of polyphosphazene in a wide optical range, the constructed phosphazene-triphenylamine (PPTA) covalent hybrid framework membranes can be reversibly switched between light gray and dark blue, with a high transmittance change of up to 79.8%@668 nm and fast switching time (<4 s). Owing to the easy one-pot fabrication and good electrochromic properties, the PPTA covalent hybrid framework membrane has great potential in various fields such as displays and dynamic optical windows.

Investigation of electrochemistry and electrochromic performance of metallopolymer formed by electropolymerization of Fe(II) complex with triphenylamine-hydrazone ligand

The complex of Fe(II) ions of general formula [FeL2](BF4)2 with triphenylamine-hydrazone ligand L has been synthesized and characterized. Oxidative electropolymerization of the complex proceeded smoothly on the working electrode producing homogenous thin film of metallopolymer. The film thickness and morphology of the layer was investigated by microscopy techniques such as SEM and AFM, and the composition of the film was confirmed by XPS analysis. It was found that after fifty successive oxidation/reduction cycles the film of thickness 120 nm was formed on the electrode surface. The metallopolymer was also characterized using cyclic voltammetry and spectroelectrochemical methods. The film was found to change its color from yellow to green-blue, high change in transmittance of 60% at 770 nm and good electrochemical stability during 375 cycles of switching of the potential between -0.1 V and +1.5 V, due to the presence of metal ions that link two ligand molecules resulting in formation of highly cross-linked film. The switching times (coloration and bleaching) were calculated to be 34.2 s and 7.3 s, respectively. Coloration efficiency of the formed film of polymeric complex was found to be 144 cm 2 /C.

Towards modulating the colour hues of isoindigo-based electrochromic polymers through variation of thiophene-based donor groups

This paper demonstrated that the hues of both neutral and oxidised colours of isoindigo-based donor–acceptor polymers could be tuned subtly by means of variation of the number and type of donor groups.

Highly electrochemically and thermally stable donor–π–acceptor triphenylamine-based hole-transporting homopolymers via oxidative polymerization

Polymers combining high electrochemical and thermal stability, good solubility, high Tg and high coke residue with low-lying HOMO levels and reasonable hole mobilities in thin films are reported in this study.

Preparation and Characterization of Intrinsic Porous Polyamides Based on Redox-Active Aromatic Diamines with Pentiptycene Scaffolds

The electrochromic (EC) polyamides (Ether-PentiTPA1 and Ether-PentiTPA8) from the electroactive pentiptycene-derived triphenylaminediamine monomers (PentiTPA1 and PentiTPA8) were designed and prepared via polycondensation. The incorporation of rigid and contorted H-shaped pentiptycene scaffolds could restrain polymer chains from close packing and further form intrinsic microporosity in the polymer matrix which could be confirmed by the measurements of WXRD, BET, and PALS. With the existence of intrinsic microporosity, the diffusion rate of counterions between the electroactive polymer film and electrolyte can be promoted during the electrochemical procedure. Therefore, the prepared polyamide Ether-PentiTPA1 exhibits enhanced EC behaviors, such as lower driving potential (1.11 V), smaller redox potential difference ΔE (0.24 V), and shorter switching response time (3.6/5.2 s for coloring/bleaching). Consequently, the formation of intrinsic microporosity can be a useful approach for the enhancement of EC response performance.

Transmissive to blackish-green NIR electrochromism in a Co(II)-based interfacial co-ordination thin film

Herein, a Co(ii)-based metallo-polymer (Co-tpy-L) with a three armed non-conjugated terpyridine ligand is synthesized using solvent-solvent interfacial polymerization. The thin film exhibits durable transmissive-to-blackish green electrochromism, selectively covering both the visible and NIR regions with a moderate voltage range of -1.4 to 0 V.

6,6'-Ditriphenylamine-2,2'-bipyridine: Coordination Chemistry and Electrochemical and Photophysical Properties

A 2,2'-bipyridine with bulky triphenylamine substituents in the 6 and 6' positions of the ligand (6,6'-ditriphenylamine-2,2'-bipyridine, 6,6'-diTPAbpy) was generated. Despite the steric bulk, the ligand readily formed bis(homoleptic) complexes with copper(I) and silver(I) ions. Unfortunately, efforts to use the 6,6'-diTPAbpy system to generate heteroleptic [Cu(6,6'-diTPAbpy)(bpy)]⁺ complexes were unsuccessful with only the [Cu(6,6'-diTPAbpy)₂](PF₆) complex observed. The 6,6'-diTPAbpy ligand could also be reacted with 6-coordinate metal ions that featured small ancillary ligands, namely, the [Re(CO)₃Cl] and [Ru(CO)₂Cl₂] fragments. While the complexes could be formed in good yields, the steric bulk of the TPA units does alter the coordination geometry. This is most readily seen in the [(6,6'-diTPAbpy)Re(CO)₃Cl] complex where the Re(I) ion is forced to sit 23° out of the plane formed by the bpy unit. The electrochemical and photophysical properties of the family of compounds were also examined. 6,6'-diTPAbpy exhibits a strong ILCT absorption band (356 nm, 50 mM^-1 cm^-1) which displays a small increase in intensity for the homoleptic complexes ([Cu(6,6'-diTPAbpy)₂]⁺; 353 nm, 72 mM^-1 cm^-1, [Ag(6,6'-diTPAbpy)₂]⁺; 353 nm, 75 mM^-1 cm^-1), despite containing 2 equiv of the ligand, attributed to an increased dihedral angle between the TPA and bpy moieties. For the 6-coordinate complexes the ILCT band is further decreased in intensity and overlaps with MLCT bands, consistent with a further increased TPA-bpy dihedral angle. Emission from the ¹ILCT state is observed at 436 nm (τ = 4.4 ns) for 6,6'-diTPAbpy and does not shift for the Cu, Ag, and Re complexes, although an additional ³MLCT emission is observed for [Re(6,6'-diTPAbpy)(CO)₃Cl] (640 nm, τ = 13.8 ns). No emission was observed for [Ru(6,6'-diTPAbpy)(CO)₂Cl₂]. Transient absorption measurements revealed the population of a ³ILCT state for the Cu and Ag complexes (τ = 80 ns). All assignments were supported by TD-DFT calculations and resonance Raman spectroscopic measurements.

Electropolymerization of D–A–D type monomers consisting of triphenylamine and substituted quinoxaline moieties for electrochromic devices

We reported three D–A–D type monomers consisting of triphenylamine and substituted quinoxaline moieties, and their electrochemical polymerization for electrochromic devices.

Highly Stable Indacenodithieno[3,2-b]thiophene-Based Donor-Acceptor Copolymers for Hybrid Electrochromic and Energy Storage Applications

Stable doping of indacenodithieno[3,2-b]thiophene (IDTT) structures enables easy color tuning and significant improvement in the charge storage capacity of electrochromic polymers, making use of their full potential as electrochromic supercapacitors and in other emerging hybrid applications. Here, the IDTT structure is copolymerized with four different donor-acceptor-donor (DAD) units, with subtle changes in their electron-donating and electron-withdrawing characters, so as to obtain four different donor-acceptor copolymers. The polymers attain important form factor requirements for electrochromic supercapacitors: desired switching between achromatic black and transparent states (L*a*b* 45.9, -3.1, -4.2/86.7, -2.2, and -2.7 for PIDTT-TBT), high optical contrast (72% for PIDTT-TBzT), and excellent electrochemical redox stability (Ired/Iox ca. 1.0 for PIDTT-EBE). Poly[indacenodithieno[3,2-b]thiophene-2,8-diyl-alt-4,7-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-2-(2-hexyldecyl)-2H-benzo[d][1,2,3]triazole-7,7'-diyl] (PIDTT-EBzE) stands out as delivering simultaneously a high contrast (69%) and doping level (>100%) and specific capacitance (260 F g-1). This work introduces IDTT-based polymers as bifunctional electro-optical materials for potential use in color-tailored, color-indicating, and self-regulating smart energy systems.

Electrosynthesis and Electrochromism of a New Crosslinked Polydithienylpyrrole with Diphenylpyrenylamine Subunits

A new electroactive monomer with two 2,5-di(2-thienyl)pyrrole (SNS) units and one diphenylpyrenylamine (DPPA) subunit, namely N,N-bis(4-(2,5-di(2-thienyl)-1H-pyrrol-1-yl)-phenyl)-1-aminopyrene (DPPA-2SNS), was synthesized from 1,4-di-(2-thienyl)butane-1,4-dione with N,N-di(4-aminophenyl)-1-aminopyrene through the Paal–Knorr condensation reaction. Visible and near-infrared (NIR) electrochromic polymer films could be facilely generated on the ITO-glass surface by the electrochemical polymerization of DPPA-2SNS in an electrolyte solution. The electro-synthesized polymer films exhibit multi-staged redox processes and multi-colored anodic electrochromic behavior. A multi-colored electrochromism, with yellowish orange, greyish blue, and purplish black colors, was observed in the polymer film by applying a positive potential. The polymer films exhibit reasonable coloration efficiency, fast response time, and good cycling stability, especially when switched between neutral and the first oxidation states. For comparison, N-(1-pyrenyl)-2,5-di(2-thienyl)pyrrole (Py-SNS) was also prepared and characterized with electrochemical and electro-optical properties.

Yellow-to-brown and yellow-to-green electrochromic devices based on complexes of transition metal ions with a triphenylamine-based ligand

Transmissive-to-colored electrochromism has been achieved by combination of MLCT of transition metal complexes with the electrochromic properties of ligand molecules. The color transitions were from yellow to dark brown for the Fe(ii) complex, yellow to orange to bluish-green for the Co(ii) complex and yellow to green for the Zn(ii) complex. By using a metal ion-ligand coordination approach, the self-assembly of hydrazone-based ligands containing a triphenylamine group with appropriate metal salts (FeCl2, Co(ClO4)2 and Zn(BF4)2) produced novel complexes of the general formula [ML2]X2. The isolated complexes were characterized by spectroscopic methods, and the Co(ii) complex also by X-ray diffraction analysis. Thin films of the complexes have been obtained by a spray-coating method and they were used in the construction of electrochromic devices, which showed good electrochromic stability, a high color contrast of 47.5% for Fe(ii), 37.2% for Co(ii) and 33.7% for Zn(ii) complexes and fast coloring and bleaching times.

An Efficient Electrochromic Supercapacitor Based on Solution-Processable Nanoporous Poly{tris[4-(3,4-ethylenedioxythiophene)phenyl]amine}

A new green synthetic route to tris[4-(3,4-ethylenedioxythiophene)phenyl]amine (TEPA) monomer has been developed and the molecular structure of TEPA has been determined by using single-crystal XRD. Solution-processable nanoporous poly{tris[4-(3,4-ethylenedioxythiophene)phenyl]amine} (PTEPA) is prepared by a chemical oxidative polymerization in a microemulsion. Based on the distorted structure of TEPA in the solid state, it is proposed that dendritic PTEPA has a distorted 3 D conformation with multiple twisted channels and pores that are narrowed and blocked by bifurcation and distortion of PTEPA, which is consistent with the observed hierarchical pore structure. As a cathode material, PTEPA exhibits a discharge capacity of 89.5 mAh g-1 in the initial cycle with a highly sloping two-stage discharge curve and relatively stable cycling performance. Beyond its excellent energy storage properties, PTEPA also shows relatively good electrochromic performance. Furthermore, an efficient all-solid-state electrochromic supercapacitor (ECSC) with good electrochromic performance and high energy storage capacity (13.3 mF cm-2 ) is assembled from PTEPA and nanoporous graphene films. During charge-discharge processes, the color of the ECSC changes between yellow-green and steel blue. Thus, the energy storage level of the ECSC can be monitored by the corresponding color changes. The fabricated ECSC may have practical applications, for example, in self-powered electrochromic smart windows.

Facile Approach of Porous Electrochromic Polyamide/ZrO2 Films for Enhancing Redox Switching Behavior

Porous redox-active polyamide hybrid films have been successfully prepared to enhance the electrochromic (EC) properties in this report comparing with salt-caused porous films and hybrid films obtained via in situ sol-gel reaction of hydroxyl groups and zirconium dioxide (ZrO₂). With the assistance of porous and hybrid structures, the diffusion rate of counterions between electrolyte and EC species could be effectively increased, and the charges could be delivered and stored between the donor-acceptor system constructed by the organic-inorganic hybrid during the electrochemical process. Furthermore, there would be a synergistic effect while combining the porous structure and hybrid system together, which can improve the EC behaviors much more obviously; that is, the enhancement of porous hybrid films is more than that of porous films and hybrid films individually. For further application, the porous hybrid films were fabricated into devices, which exhibit a lower oxidation potential (from 1.07 to 0.94 V) and shorter switching response time (from 81.3 to 9.7 s for coloring time and from 44.7 to 20.8 s for bleaching time) with good electrochemical stability. Consequently, these results indicate that the EC properties could be enhanced and improved dramatically by the facile approach of merging the porous structure and hybrid system.

Solution-Processable Copolymers Based on Triphenylamine and 3,4-Ethylenedioxythiophene: Facile Synthesis and Multielectrochromism

In comparison with traditional inorganic electrochromic materials, organic polymers offer advantages such as fast switching speed, flexibility, lightweightness, low cost and nontoxicity, solution-processability, and color tunability. Herein, a series of hyper-branched copolymers are synthesized from triphenylamine and 3,4-ethylenedioxythiophene with different feed ratios via iron(III) chloride (FeCl₃ )-mediated oxidative polymerization. The resultant organic-soluble polymers are easily processable and their corresponding electrochromic devices are found to be stable with limited degradation upon 2500 cycles. In addition to their facile synthesis to achieve solution-processable polymers, studies also show that the polymers exhibit multielectrochromic properties and give rise to five colored states upon oxidative-doping by applying an external voltage between 0 and 2.0 V, providing an interesting example of polymers with unique electrochromic switching among up to five colors, from yellow at the neutral state, to pale green, pale purple, orange, and finally gray.

Electrochromic Response Capability Enhancement with Pentiptycene-Incorporated Intrinsic Porous Polyamide Films

Enhancing switching response capability of electrochromic (EC) polymers has been a topical issue. Herein, the H-shaped nonplanar pentiptycene scaffold is successfully introduced into the polyamide film derived from N,N'-bis(4-aminophenyl)-N,N'-di(methoxyphenyl)-1,4-phenylenediamine (TPPA), and the resulting copolymer shows enhanced EC behaviors, including lower oxidation potential and shorter switching response time, as compared to the corresponding TPPA-derived homopolymer.

Dual-Switching Electrochromism and Electrofluorochromism Derived from Diphenylamine-Based Polyamides with Spirobifluorene/Pyrene as Bridged Fluorescence Units

Electrochromic (EC)/electrofluorochromic (EFC) bifunctional materials are receiving great attention because of their promising applications in optoelectronic devices. However, the development of ideal EC/EFC bifunctional materials is still a great challenge because of the poor integration of EC/EFC performances (optical contrast, response speed, and switching stability). Herein, we reported two novel diphenylamine-based mixed valence (MV) polyamides (S-HPA and P-HPA) with spirobifluorene (2,7-positions) and pyrene (1,6-positions) as bridged fluorescence units, respectively, showing impressive cyclability and fluorescence contrast with rapid switching. Through the formation of an effective electronic coupling between the two nitrogen centers using spirobifluorene/pyrene bridges, we demonstrated that different bridges have significant effects on the thermal and electrooptical characteristics of polyamides. In addition to lower fluorescence quantum yield and glass transition temperature, the S-HPA exhibited superior cyclability (contrast change <3.4%/14% over 500/300 cycles for EC/EFC switching), higher color/fluorescence contrast (64%/304%), and faster switching time (<2.6 s), mainly owing to the shorter conjugated length and more twisted configuration of the spirobifluorene bridge. The design principle of MV polymers with fluorophore bridges proposed here will be a promising way to realize high-performance EC/EFC devices and will also provide new insights into their future development and applications.

A three-step sequence strategy for facile construction of donor–acceptor type molecules: triphenylamine-substituted acenes

A new synthetic strategy was successfully developed for highly efficient construction of triphenylamine-substituted polycyclic aromatic hydrocarbons (PAHs), including anthracenes, tetraphenes, pentaphenes, and trinaphthylene. These molecules exhibited special structural characteristics, including donor–acceptor–donor (D–A–D) and donor–acceptor (D–A). Diverse aryl iodides coupled well with chlorinated 2-methyl benzaldehydes via a transient ligand-directed C–H bond arylation strategy to furnish various PAH precursors. The subsequent palladium-catalyzed Suzuki cross-couplings with 4-(diphenylamino)phenylboronic acid produced corresponding triphenylamine derivatives. Further, Brønsted acid promoted cycloaromatization generated the triphenylamine-substituted PAHs readily. The photophysical properties was investigated by UV–vis absorption and fluorescence emission spectroscope together with density functional theory (DFT) calculations.

Triphenylamine-hexaarylbiimidazole derivatives as hydrogen-acceptor photoinitiators for free radical photopolymerization under UV and LED light

In this study, three triphenylamine-based hexaarylbiimidazole (HABI) derivatives featuring different numbers of methoxy groups (none for HABI1, two for HABI2, and four for HABI3) have been synthesized.

Palladium bis-pincer complexes with controlled rigidity and inter-metal distance

We report a series of redox-active bis(pincer) Pd(ii) complexes in which the redox active units are based on either a diarylamido or a carbazolide framework.