Enhancement of Electrochromic Switching Properties with Tröger's Base-Derived Intrinsic Microporous Polyamide Films.

The formation of Tröger's Base (TB) configuration is a useful approach to synthesize polymers of intrinsic microporosity (PIM). Herein, the V-shaped TB scaffold is incorporated to prepare electrochromic (EC) polyamide with electroactive triphenylamine (TPA) moiety. The presence of intrinsic microporosity derived from inefficient packing of TB scaffolds can facilitate the counterions diffusion between electroactive species and electrolytes. Consequently, the resulting TB-based polyamide exhibits enhanced EC behaviors, such as a lower driving potential, reduced the difference of redox potentials ΔE, and shorter switching response time compared to the corresponding EC counterpart polyamide.

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.

Facile Fabrication of Triphenylamine-Based Redox-Active Nanocomposites by a Sol-Gel Method: Enhanced Electrochromic Response Capability and Stability Performance.

In this research, a new design of organic-inorganic hybrid networks involving covalently bonding, novel, electron-donating triphenylamine (TPA)-containing electroactive molecules to inorganic metal oxides is successfully developed by using a facile sol-gel process. These anodically electrochromic TPA-containing materials exhibit multicolor electrochromic behaviors at various oxidation states. By introducing zirconium oxide into electrochromic materials, not only can an excellent optical transparency in the visible light region at a neutral state be achieved given the nature of the large energy bandgap, but the electrochromic switching can also be driven by a lower oxidation potential with an enhanced response capability (shorter coloring times and bleaching times). Moreover, the hybrid films show outstanding electrochemical stability and high reversibility under long-term operations owing to their good adhesion to the electrode. Consequently, the electrochromic devices derived from these novel hybrid electroactive materials reveal a huge potential for electrochromic applications.

Electrochromism and Nonvolatile Memory Device Derived from Triphenylamine-Based Polyimides with Pendant Viologen Units.

Three novel solution-processable polyimides containing triphenylamine and pendant viologen moieties are prepared from the newly synthesized diamine and three commercially available dianhydrides. The thermally stable polyimide with strong donor-acceptor charge-transfer possesses write-once read-many-times memory behavior with excellent operation stability. The obtained multicolored electrochromic polymer films reveal ambipolar electrochemical behavior with high optical transmittance contrast of coloration changed from transmissive neutral state to the cyan/magenta/yellow redox states, implying great potential for application in smart window and displays.

Multilevel nonvolatile flexible organic field-effect transistor memories employing polyimide electrets with different charge-transfer effects.

The electrical memory characteristics of the n-channel organic field-effect transistors (OFETs) employing diverse polyimide (PI) electrets are reported. The synthesized PIs comprise identical electron donor and three different building blocks with gradually increasing electron-accepting ability. The distinct charge-transfer capabilities of these PIs result in varied type of memory behaviors from the write-one-read-many (WORM) to flash type. Finally, a prominent flexible WORM-type transistor memory is demonstrated and shows not only promising write-many-read-many (WMRM) multilevel data storage but also excellent mechanical and retention stability.

Redox-Active High-Performance Polyimides as Versatile Electrode Materials for Organic Lithium- and Sodium-Ion Batteries.

Organic electrode materials for rechargeable batteries show great promise for improving the storage capacity, reducing production costs, and minimizing environmental impact toward sustainability. In this study, we report a series of newly synthesized arylamine-based polyimides, TPPA-PIs, with three different bridge functionalizations on the imide rings and isomeric constituents that can work as versatile battery electrodes. As a lithium-ion battery cathode, a maximum energy density of 248 Wh kg-1 with high voltage operation up to 4.0 V can be achieved. As a lithium-ion battery anode, the TPPA-PIs showed a reversible storage capacity of 806 mA h g-1 at 100 mA g-1 current density with good rate capability up to a current density of 2000 mA g-1. Moreover, when applied as sodium-ion battery anodes, TPPA-PIs delivered an optimum specific capacity of up to 218 mA h g-1 after 50 cycles at a 50 mA g-1 current density and revealed a long cycling stability up to 1000 cycles under a high current density of 1000 mA g-1. More importantly, these electrochemical performances of TPPA-PIs are among the best compared with other reported polymer-based electrodes. The mechanistic studies show that both bridge functionalization on the imide units and isomerism impact the electrochemical performance by regulating their intrinsic properties such as charge storage behavior, ion diffusivity, and activation energy. We believe that such a detailed study of the structural design to electrochemical performance of these polymeric electrodes will offer insights into materials development and optimization for next-generation multifunctional energy storage devices in a wide range of applications.

Facile Blending Strategy for Boosting the Conjugated Polymer Semiconductor Transistor's Mobility.

The optimization of field-effect mobility in polymer field-effect transistors (FETs) is a critical parameter for advancing organic electronics. Today, many challenges still persist in understanding the roles of the design and processing of semiconducting polymers toward electronic performance. To address this, a facile approach to solution processing using blends of PDPP-TVT and PTPA-3CN is developed, resulting in a 3.5-fold increase in hole mobility and retained stability in electrical performance over 3 cm2 V-1 s-1 after 20 weeks. The amorphous D-A conjugated structure and strong intramolecular polarity of PTPA-3CN are identified as major contributors to the observed improvements in mobility. Additionally, the composite analysis by X-ray photoelectron spectroscopy (XPS) and the flash differential scanning calorimetry (DSC) technique showed a uniform distribution and was well mixed in binary polymer systems. This mobility enhancement technique has also been successfully applied to other polymer semiconductor systems, offering a new design strategy for blending-type organic transistor systems. This blending methodology holds great promise for the practical applications of OFETs.

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.

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.

Donor-Acceptor Effect of Carbazole-Based Conjugated Polymer Electrets on Photoresponsive Flash Organic Field-Effect Transistor Memories.

The molecular structure of polymer electrets is crucial for creating diverse functionalities of organic field-effect transistor (OFET) devices. Herein, a conceptual framework has been applied in this study to design the highly photoresponsive carbazole-based copolymer electret materials for the application of photoresponsive OFET memory. As an electret layer, two 1,8-carbazole-based copolymers were utilized; the copoly(CT) consisted of carbazole as the donor group and thiophene as the π-spacer, whereas the copoly(CBT) was further introduced as an acceptor moiety, benzothiadiazole, for comparison. Both copolymers exhibited efficient visible-light absorption and photoluminescence quenching in the film state, indicating the formation of a considerable number of nonemissive excitons, one of the crucial factors for achieving photoinduced recovery behavior in OFET memories. Compared to copoly(CT) with the pure donor system, faster and more effective photoinduced recovery behavior was discovered in the copoly(CBT) with the conjugated donor-acceptor structure because of the coexistence of the conjugated donor and acceptor groups. Thus, the dissociation of the generated excitons facilitated the stimulating of the unique ambipolar trapping property, resulting in the high-density data storage devices with multilevel current states. In addition, the nonvolatile and durable characteristics demonstrated the feasibility in application of memory and photorecorders.

Programmable digital memory devices based on nanoscale thin films of a thermally dimensionally stable polyimide.

We have fabricated electrically programmable memory devices with thermally and dimensionally stable poly(N-(N',N'-diphenyl-N'-1,4-phenyl)-N,N-4,4'-diphenylene hexafluoroisopropylidene-diphthalimide) (6F-2TPA PI) films and investigated their switching characteristics and reliability. 6F-2TPA PI films were found to reveal a conductivity of 1.0 x 10(-13)-1.0 x 10(-14) S cm(-1). The 6F-2TPA PI films exhibit versatile memory characteristics that depend on the film thickness. All the PI films are initially present in the OFF state. The PI films with a thickness of >15 to <100 nm exhibit excellent write-once-read-many-times (WORM) (i.e. fuse-type) memory characteristics with and without polarity depending on the thickness. The WORM memory devices are electrically stable, even in air ambient, for a very long time. The devices' ON/OFF current ratio is high, up to 10(10). Therefore, these WORM memory devices can provide an efficient, low-cost means of permanent data storage. On the other hand, the 100 nm thick PI films exhibit excellent dynamic random access memory (DRAM) characteristics with polarity. The ON/OFF current ratio of the DRAM devices is as high as 10(11). The observed electrical switching behaviors were found to be governed by trap-limited space-charge-limited conduction and local filament formation and further dependent on the differences between the highest occupied molecular orbital and the lowest unoccupied molecular orbital energy levels of the PI film and the work functions of the top and bottom electrodes as well as the PI film thickness. In summary, the excellent memory properties of 6F-2TPA PI make it a promising candidate material for the low-cost mass production of high density and very stable digital nonvolatile WORM and volatile DRAM memory 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.

Substituent effects of AIE-active α-cyanostilbene-containing triphenylamine derivatives on electrofluorochromic behavior.

Four aggregation-induced emission (AIE)- and electro-active cyanostilbene-based triphenylamine-containing derivatives with different substituents were synthesized to investigate their effects on the photoluminescence properties and electrochromic (EC) and electrofluorochromic (EFC) behavior of gel-type electrochromic devices (ECDs). The optical and photoluminescence properties of the obtained materials were influenced by the substituents, and revealed AIE-active characteristics, exhibiting stronger fluorescence intensity in the aggregated state than in solution. Consequently, the EFC devices could be fabricated by combining these AIE- and electro-active materials with cathodic EC heptyl viologen HV into the gel-type electrolyte system to enhance the emission intensity, on/off contrast ratio, and response capability.

Design, Synthesis, and Electrofluorochromism of New Triphenylamine Derivatives with AIE-Active Pendent Groups.

Triphenylamine (TPA) and 4,4'-dimethoxy-triphenylamine (TPAOMe) derivatives were successfully linked with two high-performance AIEgens, triphenylethylene (TPE) and benzo[ b]thiophene-1,1-dioxide (BTO), to obtain four aggregation-induced emission and electro-active materials, TPETPA, BTOTPA, TPETPAOMe, and BTOTPAOMe. The effects on photoluminescence characteristics and electrochromic (EC) and electrofluorochromic (EFC) behaviors in cross-linking gel-type devices derived from the prepared materials were systematically investigated. Furthermore, heptyl viologen was introduced into the EFC devices to enhance EC performance including lower working potential, faster switching time, and superior stability.

A novel panchromatic shutter based on an ambipolar electrochromic system without supporting electrolyte.

Two triphenylamine derivatives, N,N,N',N'-tetrakis(4-methoxyphenyl)-1,4-phenylenediamine TPPA and N,N,N',N'-tetrakis(4-methoxyphenyl)-1,1'-biphenyl-4,4'-diamine TPB, were successfully prepared and combined with HV to fabricate the electrochromic device as a panchromatic shutter for the application of transparent display. The obtained electrochromic device exhibits exceptional novel electrochromic properties, including enhanced color contrast, switching time, and long-term stability. Furthermore, it is worth mentioning that the most important contribution of this ambipolar system approach is that no supporting electrolyte is added into the device.

A facile approach to prepare porous polyamide films with enhanced electrochromic performance.

Novel electroactive triphenylamine-based polyamide (PA) films with a purposeful porous structure have been designed and prepared by a simple route. Polymer thin films containing well dispersed electrolyte salts were prepared first, then channels of pores could be generated within the polymer film by washing the salts out. With the help of the porous channels, the diffusion rate between electroactive species and the electrolyte during the electrochemical process could be effectively increased. Consequently, the driving potential and electrochromic response time can be efficiently improved through this approach. Novel porous PA films with optimal results both in optical transparency and electrochemical properties could be readily obtained by choosing a commonly used supporting electrolyte TBABF4 as a salt in this study. When the PA films containing un-washed TBABF4 salt were further assembled into electrochromic devices (ECDs), the salt could then be leached out during the electrochemical redox switching process to form a porous film structure and also serves as a supporting electrolyte in ECDs simultaneously. Therefore, EC performance such as the driving potential and response time could be enhanced obviously by this simplified fabrication procedure of ECDs.

Novel Organic Phototransistor-Based Nonvolatile Memory Integrated with UV-Sensing/Green-Emissive Aggregation Enhanced Emission (AEE)-Active Aromatic Polyamide Electret Layer.

A novel aggregation enhanced emission (AEE)-active polyamide TPA-CN-TPE with a high photoluminesence characteristic was successfully synthesized by the direct polymerization of 4-cyanotriphenyl diamine (TPA-CN) and tetraphenylethene (TPE)-containing dicarboxylic acid. The obtained luminescent polyamide plays a significant role as the polymer electret layer in organic field-effect transistors (OFETs)-type memory. The strong green emission of TPA-CN-TPE under ultraviolet (UV) irradiation can be directly absorbed by the pentacene channel, displaying a light-induced programming and voltage-driven erasing organic phototransistor-based nonvolatile memory. Memory window can be effectively manipulated between the programming and erasing states by applying UV light illumination and electrical field, respectively. The photoinduced memory behavior can be maintained for over 104 s between these two states with an on/off ratio of 104, and the memory switching can be steadily operated for many cycles. With high photoresponsivity ( R) and photosensitivity ( S), this organic phototransistor integrated with AEE-active polyamide electret layer could serve as an excellent candidate for UV photodetectors in optical applications. For comparison, an AEE-inactive aromatic polyimide TPA-PIS electret with much weaker solid-state emission was also applied in the same OFETs device architecture, but this device did not show any UV-sensitive and UV-induced memory characteristics, which further confirmed the significance of the light-emitting capability of the electret layer.

Highly transparent AgNW/PDMS stretchable electrodes for elastomeric electrochromic devices.

Stretchable conductors based on silver nanowires (AgNWs) and polydimethylsiloxane (PDMS) have been studied extensively for many years. However, it is still difficult to achieve high transparency with low resistance due to the low attractive force between AgNWs and PDMS. In this paper, we report an effective method to transfer AgNWs into PDMS by using substrates which have a hydrophobic surface, and successfully prepared stretchable AgNW/PDMS electrodes having high transparency and low sheet resistance at the same time. The obtained electrodes can be stretched, twisted, and folded without significant loss of conductivity. Furthermore, a novel elastomeric HV electrochromic device (ECD) fabricated based on these stretchable AgNW/PDMS hybrid electrodes exhibited excellent electrochromic behavior in the full AgNW electrode system and could change color between colorless and blue even after 100 switching cycles. As most existing electrochromic devices are based on ITO and other rigid conductors, elastomeric conductors demonstrate advantages for next-generation electronics such as stretchable, wearable, and flexible optoelectronic applications.

Synthesis and Electrochromism of Highly Organosoluble Polyamides and Polyimides with Bulky Trityl-Substituted Triphenylamine Units.

Two series of polyamides and polyimides containing bulky trityl-substituted triphenylamine units were synthesized from condensation reactions of 4,4'-diamino-4''-trityltriphenylamine with various dicarboxylic acids and tetracarboxylic dianhydrides, respectively. The polymers showed good solubility and film-forming ability. Flexible or robust films could be readily obtained via solution-casting. The use of aliphatic diacid or dianhydride reduces interchain charge transfer complexing and leads to colorless polyamide and polyimide films. These polymers showed glass-transition temperatures in the range of 206⁻336 °C. Cyclic voltammograms of the polyamide and polyimide films displayed reversible electrochemical oxidation processes in the range of 0⁻1.0 or 0⁻1.3 V. Upon oxidation, the color of polymer films changes from colorless to blue-green or blue. As compared to the polyimide counterparts, the polyamides showed lower oxidation potentials and thus a higher electrochromic stability and coloration efficiency. Simple electrochromic devices were also fabricated as a preliminary investigation for electrochromic applications of the prepared polymers.

Optically Isotropic, Colorless, and Flexible PITEs/TiO2 and ZrO2 Hybrid Films with Tunable Refractive Index, Abbe Number, and Memory Properties.

A series of novel polyimidothioethers (PITEs) and the respective polymer hybrids of titania or zirconia with fantastic thermal stability and optical properties have been successfully prepared. These colorless PITEs with high transparency were synthesized by Michael polyaddition from commercially available dithiol and bismaleimides monomers. The PITE with sulfide and hydroxyl groups (S-OH) and the corresponding hybrid films declare ultra-lowest birefringence value of 0.002 and tunable refractive index (1.65-1.81 for S-OH/titania and 1.65-1.80 for S-OH/zirconia), implying large potential to the optical applications in the future. Moreover, the S-OH/zirconia hybrid films exhibit higher Abbe's number and optical transparency than those of S-OH/titania system because larger energy band gap of ZrO2. Furthermore, by adding titania and zirconia as electron acceptor into S-OH system, the charge transfer complex can be facilitated and stabilized caused by the lower LUMO energy level of hybrid materials. Consequently, the devices of memory prepared from these polymer films of hybrid showed interesting and adjustable memory behavior from DRAM, SRAM, to WORM at various titania or zirconia contents with a large ON/OFF ratio (108), denoting that the memory devices derived from these highly transparent novel S-OH/TiO2 and S-OH/ZrO2 hybrid films are attractive for the electrical applications.