Conjugated and Non-conjugated Polymers Containing Two-Electron Redox Dihydrophenazines for Lithium-Organic Batteries.

Organic p-type cathode materials have recently attracted increasing attention due to their higher redox potentials and rate capabilities in comparison to n-type cathodes. However, most of the p-type cathodes based on one-electron redox still suffer from limited stability and low specific capacity (<150 mAh g-1 ). Herein, two polymers, conjugated poly(diethyldihydrophenazine vinylene) (CPP) and non-conjugated poly(diethyldihydrophenazine ethylidene) (NCPP) containing two-electron redox dihydrophenazine, have been developed as p-type cathode materials. It is experimentally and theoretically found that the conjugated linkage among the redox centers in polymer CPP is more favorable for the effective charge delocalization on the conjugated polymer backbone and the sufficient oxidation in the higher potential region (3.3-4.2 V vs. Li/Li+ ). Consequently, the CPP cathode displays a higher reversible specific capacity of 184 mAh g-1 with excellent cycling stability.

Water-Based Additive-Free Chromic Inks for Printing of Flexible Photochromics and Electrochromics.

Digital inkjet printing has become one of the most convenient and efficient technologies for coating chromic materials on flexible substrates with complicated patterns. However, the development of water-based, additive-free chromic inks for inkjet printing still remains a challenge. Herein, three ammonium-functionalized colorless viologen derivatives AV, APV, and AQV with excellent water solubilities are utilized as chromes in the chromic inks due to their excellent photochromic and electrochromic properties. Water, ethanol, and ethylene glycol are selected as cosolvents, and their contents in this ternary solvent system have been optimized to achieve comprehensive rheological properties. With the H2O:EtOH:EG weight ratio of 8:1:7, the chromic ink based on AV realizes a viscosity of 4.69 mPa·s, a surface tension of 45.13 mN/m, and a Z value of 3.87. Without adding any additive, the as-prepared chromic inks can be printed on flexible substrates, such as paper and poly(ethylene terephthalate) (PET) films, by a conventional inkjet printer with inherent high resolutions. The printed patterns are initially invisible due to the colorless characteristics of the chromic inks. Interestingly, the printed films are responsive to both light and electric stimuli. Upon irradiation by UV light, a series of sentences with font sizes from 5 to 12 points and four quick response codes with different lattice resolutions clearly appear on the printed paper. Meanwhile, after printing on an indium tin oxide-coated PET substrate, electrochromic devices (ECDs) can be facilely fabricated by covering a hydrogel electrolyte on the printed films. Upon application of different potentials, the assembled ECDs exhibit "Peking Opera facial makeup" patterns with different colors. Therefore, the developed water-based additive-free chromic inks can be utilized for information display and encryption applications.

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.

Colorless-to-Black Electrochromism from Binary Electrochromes toward Multifunctional Displays.

Cyclohexane-1,2,4,5-tetracarboxylic diimide with a nonconjugated core has been incorporated to bridge two conventional triphenylamine units. The obtained monomer has successfully hypsochromically shifted the maximum absorption wavelength by 10 nm in comparison to the one with a pyromellitic diimide bridge. Consequently, a colorless electrochromic (EC) polymer poly(bis(N,N-diphenyl-4-aminophenyl)cyclohexane-1,2,4,5-tetracarboxylic diimide) (PTPA-HDI) was electropolymerized on indium tin oxide (ITO)-coated glass. The morphology, absorption, and spectroelectrochemistry properties of polymer PTPA-HDI films electropolymerized by different scan cycles have been systematically investigated. It is found that comprehensive properties, such as color contrast and initial transparence, can be achieved for the polymer film electropolymerized by 15 scan cycles. Moreover, to realize colorless-to-black electrochromism, an asymmetric viologen derivative 1-(4-cyanophenyl)-1'-hexyl-4,4'-bipyridinium dihexafluorophosphate (HVCN) has been designed and straightforward synthesized. With the introduction of a cyanophenyl group and a hexyl chain on the two pyridinium units, colorless-to-green electrochromism can be realized for this processible viologen derivative. The absorption band at 495 nm of colorated PTPA-HDI compensates well for the valley in the absorption spectrum of colorated HVCN. Therefore, different types of colorless-to-black electrochromic devices (ECDs) are fabricated using polymer PTPA-HDI-deposited ITO electrode and HVCN-based gel electrolyte. Such a supporting electrolyte-free ECD with binary electrochromes exhibits fast coloration, high color contrast, and excellent reversibility. Furthermore, an encryption ECD is demonstrated by switching a black two-dimensional code. In addition, an autodigital display is integrated on a smart window and hence different functions can be realized in a single ECD. Overall, this study may facilitate the understanding of the EC behaviors of binary electrochromes and present a new path to design multifunctional displays.