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

Abstract

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.

Bistable Elastic Electrochromic Ionic Gels for Energy-Saving Displays

“…The coloring layer is the core component of electrochromic (EC) devices, which is closely related to their response performance, color contrast, coloring uniformity, and bistability. − The high flexibility of the electrochromic layer is the key to ensure the good performance and stability of the devices. At present, the electrochromic films of small organic molecules are mainly prepared by solvent volatilization on the basis of PMMA gels, , while the electrochromic films prepared by other polymer materials are rarely reported. − It is mainly because the PMMA film has excellent film-forming properties, transparency, and mechanical strength, which is incomparable to other polymer materials.…”

Exploring Isomeric Effects on Optical and Electrochemical Properties of Red/Orange Electrochromic Polymers

“…Tailoring polymer structures that absorb in the high-gap region of the visible spectrum is challenging due to the difficulty in balancing desired optical features with electrochemical properties. High-gap ECPs are desirable from a practical point of view due to their utility as components of subtractive color mixing ECP blends to access various secondary colors around the color palette or blacks and browns via coprocessing. − One major limitation for these blends is the long-term switching stability between colored and transmissive states due to the instability of chemical structures that absorb in this region of the visible spectrum. Therefore, it is necessary to establish effective design strategies for synthesizing electrochemically stable high-gap ECPs.…”

Preparation and electrochromic properties of polyamides based on 3,4‐dimethylthieno[2,3‐b]thiophene

“…Triphenylamine series organic electrochromic materials had become a research hotspot in the field of electrochromism because of the high coloring efficiency and polychromatic properties. Nevertheless, in comparison to other color types, electrochromism had many unique advantages, such as low energy consumption, low working voltage, many and high color states, good cycling durability and reversible, reasonable memory effect and so on 5,6 . Therefore, electrochromism had been applied in a variety of commercial applications, such as smart windows, biosensors, display devices, optical communications, glass mirrors and thermal control of spacecraft 1,7 …”