No abstract

Two types of thiophene derivatives, i.e., thiophene (T) and 3,4-ethylenedioxylthiophene (ET) with a single thiophene ring, while thieno[3,2-b]thiophene (TT) and 2,2’-bithiophene (BT) with double thiophene rings, have been inserted between...

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,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 ammoniumand 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.

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-1,2,4,5tetracarboxylic 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-HDIdeposited 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.

Inserting a conjugated bridge between the two pyridinium units of the viologen is an effective approach to tuning the colorations of the viologen derivatives. However, the relationship between the charge density on the viologen bridge and the related photochromic (PC) and electrochromic (EC) properties has been rarely studied. Herein, three conjugated bridges with different charge densities, i.e., thienyl, phenyl, and quinoxalinyl groups, are incorporated between the two pyridinium units of ammonium‐functionalized viologens. The coloration scope of the viologens before and after chromism is expanded due to the adjusted intramolecular charge transfer interactions. Moreover, the introduction of an electron‐withdrawing bridge is greatly beneficial to the chromic properties of the conjugation‐extended viologens in polyacrylamide hydrogels. The EC device based on AQV hydrogel exhibits the highest optical contrast of 85% at 580 nm, the fastest switching time (1.0 and 0.9 s for coloration and bleaching processes, respectively), and no decay in optical contrast after 1000 EC cycles. Furthermore, multifunctional and multicolored signages as sports icons and traffic signs are fabricated and demonstrated. Variable traffic signs presenting “Permitted”, “Warning”, and “Prohibited” cautions for pedestrians and vehicles can be realized in a single device with only one piece of ITO glass.