Copolymers with thiophene systems

Copolymers of thiophenes and didodecyloxybenzenes have been synthesized as well, exhibiting multicolor electrochromism coupled with high contrast ratios and fast response times (Scheme 8) [45]. Since all three basic colors in the RGB (red-green-blue) system can be obtained, the material is a potential candidate for display applications. 

Novel materials were prepared by electrochemical copolymerization of thiophene with thiophene-3-acetic acid (XV) [49], The incorporation of the —COOH group allows for the loading of metal catalysts into these systems. These copolymers were soluble and had high degrees of polymerization (>2000). Copolymers between 3-methylthiophene and ferrocene esters of 2-(3-thienyl-ethanol) with varying alkyl chain lengths have been prepared (XVI) [50]. 

Copolymerization of thiophenes and pyrroles offers the promise of combining the higher stability associated with thiophene-based polymers with the higher conductivity characteristic of polypyrroles. Three different methods have been used to prepare such copolymers. These are (1) direct copolymerization of pyrrole and thiophene monomer mixtures, (2) copolymerization of pyrrole with bi- or a-terthiophene, and (3) polymerization ofa-linked pyrrole-thiophene monomers. The last case includes both two- and three-ring systems. 

Another PF copolymer 28, composed of alternating DOF and thieno-[3,2-b]thiophene, was reported by Iim et al. [59]. The incorporation of electron-rich thieno- [ 3,2- b ] thiophene moiety in the polymer backbone led to lower HOMO (5.38 eV) and higher LUMO (2.4 eV) levels than those of PFO (HOMO 5.8 eV, LUMO 2.12 eV [12]). The device ITO/PEDOT PSS/28/IiF/Al exhibited a pure green emission with a peak at 515 nm and CIE coordinates of (0.29, 0.63), which is very close to the standard green required by the National Television System Committee (NTSC) (0.26, 0.65). In addition, the maximum brightness and efficiency of this device were 970 cdm 2 and 0.32 cd A-1, respectively. 

The polymers described in Sect. 2.3 can be considered to be copolymers, and in many cases they are actually called copolymers. However, those polymers have been synthesized from monomers with polymerizable groups (e.g., thiophene), and the monomer already contains the redox functionality. The copolymers that will now be discussed have been prepared from two or more difierent monomers, which can also be electropolymerized separately, and the usual strategy is to mix the monomers and execute the electropolymerization of this mixed system. It should be mentioned that the structures of the copolymers have not been clarified unambiguously in many cases. Usually the cyclic voltammetric responses detected show the characteristics of both polymers, and so it is difficult to establish whether the surface layer consists of a copolymer or whether it is a composite material of the two polymers. However, several copolymers exhibit electrochemical behaviors that differ from the polymers prepared from the respective monomers. The properties of the copolymer depends on the molar ratio of the monomers (feed rate), and can be altered by other experimental conditions such as scan rate, pH, etc., since generally the electrooxidation of one of the comonomers is much faster than that of the other one (a typical example is the comonomer aniline, whose rate of electropolymerization is high even at relatively low positive potentials). In many cases the new materials have new and advantageous properties, and it is the aim of these studies to discover and explore these properties. We present a few examples below. 

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