Considerable interest is raised by organic materials owing to their exceptional performance in electronic and optoelectronic applications. Among these, electrochromic materials (EC) that can be switched between a distinct color and a bleached state exhibiting high contrast, multicolor and improved long-term stability are attractive in the fabrication of electrochromic devices (ECDs). Ionic materials, in particular, have received persistent attention owing to their tunable optical and electronic properties. 4,4′-Bipyridinium salts, commonly called viologens (V2+), are a well-recognized class of electrochromic materials that exhibit three reversible redox states, namely, V2+ (dication, pale yellow colored/colorless) ↔ V+˙ (radical cation, violet/blue/green) ↔ V0 (neutral, colorless). The electrochromic properties of these materials can be modulated by varying the nitrogen substituents on the pyridyl ‘N’; also, besides this, varying the counter ions with specific functionalities has been shown to enhance the electrochromic behavior, such as switching time, cycling stability and device performance. Although ECDs based on viologens are well regarded for their low operational voltages, they exhibit certain disadvantages such as low cycle life and poor efficiency of the device in the long term. Extensive efforts have been made to fine tune the EC properties of viologens, either through alteration or by adding suitable electrochromic counter electrode materials, which includes the incorporation of conducting polymers in the device set-up and/or the addition of complementary redox species. Optimization of the device parameters has shown that the addition of such external agents has a positive effect on the overall device performance. This review describes recent developments in the synthesis of viologen-based electrochromes with co-redox species and their ECD performance.

Viologen-based electrochromic materials and devices

Design and preparation of triphenylamine-based polymeric materials towards emergent optoelectronic applications

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 (BT...

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

A metal complex nanosheet was synthesized by the liquid-liquid interface self-assembly method from a star-shaped ligand of tris[4-(4'-2,2':6',2''-terpyridyl)-phenyl]amine in organic solvents and metal ion Fe(ii) in water solution. The as-prepared nanosheet possessed excessively smooth morphology with a thickness of hundreds of nanometers. Adhering to an ITO glass, the nanosheet showed noticeable electrochromism from purplish red at 0 V to orange-yellow at 1.4 V and green at 1.6 V. Besides, the nanosheet exhibited outstanding stability with the optical contrast maintained at almost 100% of its original electrochemical activity over 500 cycles. The liquid-liquid interface self-assembly method was proven to be promising to prepare a polymeric metal complex for potential electrochromic applications.

Multi-color electrochromism from coordination nanosheets based on a terpyridine-Fe(II) complex

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

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...

Synthesis and Characterization of Novel Triarylamine Derivatives with Dimethylamino Substituents for Application in Optoelectronic Devices.

Two new triphenylamine-containing ambipolar electrochromic materials with ether linkages, 1-(2-(4-(bis(4-methoxyphenyl)amino)phenoxy)ethyl)-1′-ethyl-[4,4′-bipyridine]-1,1′-diium tetrafluoroborate (TPA-Vio) and 2-(4-(bis(4-methoxyphenyl)amino)phenoxy)anthracene-9,10-dione (TPA-OAQ), were successfully synthesized and fabricated into novel electrochromic devices. These devices demonstrated interesting and much higher performance than devices derived from TPA-3OMe with respect to driving voltage, switching time, and electrochromic stability.

Preparation and optoelectronic behaviours of novel electrochromic devices based on triphenylamine-containing ambipolar materials

Synthesis, characterization and electrochromic properties of novel redox triarylamine-based aromatic polyethers with methoxy protecting groups

A series of novel redox-active triphenylamine-based materials, 4,4′-bis(4,4′-dimethoxydiphenylaminyl)-4′′-methoxytriphenylamine (BDATPA) and four related derivatives, including tris(4-methoxyphenyl)amine (TPA), N,N,N′,N′-tetrakis(4-methoxyphenyl)-1,4-phenylenediamine (TPPA), N,N,N′,N′-tetrakis(4-methoxyphenyl)-1,1′-biphenyl-4,4′-diamine (TPB) and tris(4-(4,4′-dimethoxyphenylaminyl)phenyl)amine (TPAPA), were readily prepared and their electrochemical, photoluminescence (PL) and electrochromic (EC) behaviors were investigated. Interestingly, only TPB exhibited high PL intensities in both solution and solid state, while the others revealed a much lower PL intensity in solution. All of these electroactive materials showed excellent electrochemical reversibility by cyclic voltammetry scanning with multi-color changes at the related oxidation states. Furthermore, UV-Vis and spectroelectrochemical measurements were also applied to evaluate and calculate the molar extinction coefficients in order to facilitate these materials as a color palette.

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Jung-Tsu Wu

Papers

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

Synthesis and Characterization of Novel Triarylamine Derivatives with Dimethylamino Substituents for Application in Optoelectronic Devices.

Preparation and optoelectronic behaviours of novel electrochromic devices based on triphenylamine-containing ambipolar materials

Synthesis, characterization and electrochromic properties of novel redox triarylamine-based aromatic polyethers with methoxy protecting groups

Correction: Synthesis and optical properties of redox-active triphenylamine-based derivatives with methoxy protecting groups