Thiophene-based electrochromic materials

Michael A. Invernale, Muge Acik and Gregory A. Sotzing 

Handbook of Thiophene-based Materials Applications in Organic Electronics and Photonics Edited by Igor F. Perepichka and Dmitrii F. Perepichka (c) 2009 John Wiley Sons, Ltd 

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Thiophene-based Electrochromic Materials 777 Table 20.2 Electrochromic polymers with colors in both doped and undoped states... 

The large family of thiophene-based polymers is widely used in electrochromics. Table 20.2 reports the molecular stfuctures and colors (in doped and neutral states) of several thiophene-based organic materials [29],... 

Thiophene-based polymers are particularly interesting because they are stable against oxygen and moisture in both doped and undoped states. Gamier et al [12] indicated that poly(3-methylthiophene) is a promising electrochromic material with high stability to repeated potential pulses. 

Sufficiently high coloration efficiencies of electrochromic materials can be used to develop very rapid, efficient displays and light modulators. Eor example, the unusually high coloration efficiency of poly(3,4-ethylenedioxythiophene-didodecyloxybenzene) (PEB) could be effected in the presence of tungsten trioxide (WO3) as a counter electrode. This PEB-WO3 device was reported to have a maximum coloration efficiency of 1250 cm C at 552 nm [11]. The coloration properties and efficiencies for the PEB cell can be compared with those of other thiophene-based systems, such as PEDOT, as shown in Table 20.1 [11]. 

Thiophene-based polymers exhibit high conductivities in their doped states, offering good processability and interesting optical and electronic properties. Due to their exhibition of diverse color variations and their high contrast ratios, functionalized polythiophenes have become popular as electrochromic materials. 

Poly (thiophene)s are of particular interest as electfochromic materials owing to their chemical stability, ease of synthesis and processability. For the most part, current research has been focused on composites, blends and copolymer formations of several conjugated polyheterocyclics, polythiophene and its derivatives, especially PEIX)T. In one example, poly(3,4-ethylenedioxythiophene) (PEDOT)/poly(2-acrylamido-2-methyl-l-propanesulfonate) (PAMPS) composite films were prepared by Sonmez et al. for alternative electrochromic applications [50]. Thin composite films comprised of PEDOT/PAMPS were reported to switch rapidly between oxidized and neufial states, in less than 0.4 s, with an initial optical contrast of 76% at A.max. 615 nm. Nanostructured blends of electrochromic polymers such as polypyrrole and poly(3,4-ethylenedioxythiophene) were developed via self-assembly by Inganas etal. for application as an electrochromic window [26]. Uniir etal. developed a graft-type electrochromic copolymer of polythiophene and polytetrahydrofuran for use in elecfiochromic devices [51]. Two EDOT-based copolymers, poly[(3,4-ethylenedioxythiophene)-aZ/-(2,5-dioctyloxyphenylene)] and poly[(3,4-ethylenedioxythiophene)-aft-(9,9 -dioctylfluorene)] were developed by Aubert et al. as other candidates for electrochromic device development [52],... 

Besides the possibility of inserting fluorescent substituents in only one monomer unit, such as pyrrole or thiophene, it is noteworthy that suitable fluorescent groups have been appended in dimeric or trimeric monomer systems. Using this approach, Cihaner and Algi have initiated a programme aimed at the design and synthesis of photo- and electroactive polymer materials based on 2,5-di(2-thienyl)pyrroles (SNS). This system consist of thiophene and pyrrole rings interconnected by their a-positions and exhibit intense blue emission upon irradiation. They have reported the synthesis and characterisation of a series of novel fluorescent and electrochromic polymers based on N-substituted... 

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