Polythiophenes and their basic properties

Polythiophenes and their derivatives have been intensely studied due to their interesting electronic properties. Owing to the combination of their electronic properties, environmental stability, stmctural versatility, low bandgap, low cost and ease of preparation, polythiophene and its derivatives have been utilized in the development of many new electrochromic devices. Here, we focus on the use of polythiophenes for electrochromic applications in terms of their basic properties bandgap and its relation to stability, chain length of substituted functional groups and optical properties such as electrochromic contrast (with some examples from the literature). 

Because of their high solubility and desirable electrical and optical properties, poly(3-alkoxythiophene)s have been among the most popular derivatives chosen for study. Zotti etal. [54] and Tourillon [55] observed that the poly(3-alkoxythiophene)s possess a lower bandgap and a lower oxidation potential due to the electron-donating effect of the alkoxy substituent, resulting in a polymeric material with high stability in the doped form compared with poly(3-alkylthiophene)s. 

Reprinted from F. Carpi, D. De Rossi, Colors from electroactive polymers electrochromic, electroluminescent and laser devices based on organic materials. Opt. Laser Technol. 38, 292 (2006), Copyright 2006, with permission from Elsevier. 

Due to the length of the alkoxy and alkyl substituents, substituted polythiophenes, such as poly(4,4 -dimethoxy-3 -methyl-2,2 5, 2 -terthiophene) (PDMTT) and poly(4,4 -dipentoxy-3 -dodecyl-2,2 5, 2 -terthiophene) (PDDTT), differ in their spectroelectrochemical and photoelectrochemical properties [56]. It was demonstrated that the maximum absorption wavelength of poly 3-[12-(jt -methoxyphenoxy) alkyljthiophene] also depends on the alkyl chain length of the substituted monomer [15], 

Polythiophenes present a multitude of color contrasts. These polymers, with a functional group terminal to a flexible alkyl chain at the 3-position of the ring, are used for many specialized applications. One such candidate of this class is poly(3-[12-(/7-methoxyphenoxy)dodecyl]thiophene [poly(12-MPDDT)], synthesized by Ribeiro et al., which exhibited a deposition charge of ca. 65 mCcm presented greater stability over a large number of redox cycles ( 1000), a chromatic contrast of 40 % at 725 nm, a Coulombic efficiency of 80 % and good optical memory in the neutral state (E = 0.0 V) [15]. 

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