Bithiophene or terthiophene

Wei Y, Chan CC, Tian J, Jang GW, Hsueh KF (1991) Electrochemical polymerization of thiophenes in the presence of bithiophene or terthiophene kinetics and mechanisms of polymerization. Chem Mater 3 888-897... 

An alternative way to get better structural regularity might be to begin with bithiophene or terthiophene where some of the inter-ring bonds in the polymer are formed before the polymerization and these monomers have lower oxidation potentials (thiophene 1.6 V, bithiophene 1.2 V and terthiophene 1.0 V v SCE). Polymerizations of both bithiophene 143) and terthiophene 144) have been described but there is some doubt about whether the polymers derived from oligomers are more regular or... 

A number of dendrimers (395 100) of the first generation containing bithiophene or terthiophene units linked directly to silicon atoms have been reported (06MI3040 07OM5165 08OL2735). 

Functionalized PT derivatives based on EDOT have been synthesized following two main approaches. The first one relies on the direct functionalization at the ethylene bridge to give monomeric precursors suitable for polymerization while in the second one, the functional group is grafted on one thiophene cycle incorporated in an EDOT-containing bithiophene or terthiophene structure. 

Other workers have minimized overoxidation during polymerization by using bithiophenes or terthiophenes as starting materials for the polymerization process. The polymerization potential has been shown to decrease according to terthiophene < bithiophene < thiophene. But, as reviewed by Roncali, polythiophenes produced from these starting materials generally have lower conductivity. ... 

Another mechanistic possibility is the attack of the thiophene cation radical (420) upon a neutral thiophene monomer (419) to form a cation-radical dimer (421) [247]. The oxidation and loss of two protons leads to formation of the neutral dimer (422). Once again, rapid oxidation of the dimer occurs upon its formation due to its close proximity to the electrode surface and its lower oxidation potential. The cation-radical dimer (423) which is formed then reacts with another monomer molecule in a similar series of steps to produce the trimer 425. A kinetic study of the electrochemical polymerization of thiophene and 3-alkylthiophenes led to the proposal of this mechanism (Fig. 61) [247]. The rate-determining step in this series of reactions is the oxidation of the thiophene monomer. The reaction is first order in monomer concentration. The addition of small amounts of 2,2 -bithiophene or 2,2 5, 2"-terthiophene to the reaction resulted in a significant increase in the rate of polymerization and in a lowering of the applied potential necessary for the polymerization reaction. In this case the reaction was 0.5 order in the concentration of the additive. 

As in the cases of pyrrole and aniline polymers, both chemical and electrochemical procedures have been employed in the synthesis of polythiophene (PTH) and its derivatives. The thiophene polymers exhibit remarkable stability in air and water [119], The alkyl-substituted derivatives also exhibit a high degree of processability [120,121]. PTH has also been synthesized from bithiophane (the dimer) or terthiophene (the trimer). The resulting poly(2,2 -bithiophene) (PbTH) and polyterthiophene (PtTH) are more ordered than PTH and appear to have the same basic structure as the starting monomer [117,122],... 

Polythiophene (PT, Figure 9.4D) is the most easily functionalized of the polymer systems surveyed here. While the bulk of polythiophenes have been used as cathode materials, there are several systems that have been found to n-dope these are used as anode materials. In general, PTs typically exhibit a specific charge of 25-100 Ah/kg and a specific energy of 50-325 Wh/kg. Polythiophene electrochemically synthesized from bithiophene [115-117] or terthiophene [118] exhibits, as predicted, cleaner electrochemistry and more stable battery materials. Poly(3-methylthiophene) (PMT, Figure 9.4E) is well studied [119-122], with specific charge ca. 90 Ah/kg and one report of specific energy of 326 Wh/kg [123]. In nonaqueous... 

Miller and co-workers [100] described the electrochemical behavior of bithiophene and terthiophene whose terminal a-positions have been blocked with methyl or methylsulfanyl substituents to prevent polymerization. As expected, due to the presence of methyl blocking groups, anodic oxidation of dimethyl-terthiophene 26 undergoes a one reversible oxidation (Eqx = 0.99 V vs SCE). When stronger electron-donor groups such as methylsulfanyl are used, the oxidized states of both bithiophene 27 and terthiophene 28 cores are stabilized (Scheme 9.19). Consequently, their CV traces exhibit two one-electron reversible redox couples associated with the formation of stable radical cations and dications (Eox = 0.93 and Eox = 1.17 V vs SCE for 27 and ox = 0.89 and Eox = 1.02 V vs SCE for 28). As already discussed, the difference... 

Scheme 1. Inclusion complexes formed by flCD or HP0CD with bithiophene and terthiophene in aqueous solution...

The Leclerc group synthesis used DHAP to prepare copolymers containing bithiophene and terthiophene with TPD and FPD monomers." " The polymers are prepared by charging a microwave vial with the dibrominated thiophene, 5-alkylthieno-[3,4-c]pyrrole-4,6-dione (TPD) or 5-alkylfuro[3,4-c]pyrrole-4,6-dione (FPD), Herrmann-Beller catalyst (4mol%), tri(o-anisole)-phosphine (8mol%), CS2CO3 (2.3 equiv), and pivalic acid (0.3 equiv.) (Scheme 19.11). Toluene (0.2 M) is added and the reaction mixture heated to 120 °C under pressure for 24 36 h. The workup for the reaction is the same as that outlined in Example 2. Polymers 36-39 are prepared in moderate to high yields (38-94%). ... 

A new method of preparation of electrically conductive PT and PAT (e.g. n = 1, PMT) is the direct oxidation of thiophene or 3-alkylthiophene in the presence of a small amount of bithiophene with ferric perchlorate. The obtained PMT has higher electrical conductivity (about 30 S cm ) than those prepared by the conventional method of polycondensation of 2,5-dihalo-3-methyl-thiophene [576]. A simultaneous polymerization and doping of bithiophene and terthiophene can be carried out with thallium(III) trifluoroacetate in trifluoro-acetic acid [577]. 

Additives. The presence of bithiophene and terthiophene in the polymerization system enhances the regularity of the structure of the polymer chains (PAT with n = 5, 6). The molecular weight becomes lower with an increasing amount of additives [651,652]. A significant increase in the rate of polymerization of thiophene and 3-alkylthiophene (n = 1), and a decrease in the required applied potential and of the number of nucleation sites of the polymers on the surface of the electrode is observed. Since the oxidation potential of bithiophene is lower than that of thiophene monomer, the bithiophene in the polymerization system should be oxidized first, leading to nucleation species on which the polymer grows. There is no apparent structural difference between the polymers produced in the absence and in the presence of these additives [576,653,690]. The electrochemical polymerization of 3-alkylthiophene is also significantly facilitated by the presence of a small amount of indole, 5-methoxyindole, or 2,2 -bipyrrole [690]. 

An approach that eliminates head-to-head couplings in regiorandom polymers involves the use of certain Internally substituted bithiophenes and terthiophenes as monomers (e.g. 3-alkyl-2,2 -bithiophenes and 3 -alkyl-2,2 5 ,2 -terthiophenes). Chemical oxidation or coupling results in regiorandom polymers possessing no head-... 

The thiophene dimer and trimer have been electrochemically polymerized to grow poly thiophene films at lower potentials [248]. The dimer—2,2 -bithiophene—polymerizes at 1.2 V (versus SCE) to produce polythiophene with conductivities up to I S cm" [249]. The trimer— -terthiophene (2,2 5, 2"-terthienyl)—electrochemically polymerizes at 1.0 V (versus SCE) to yield films with conductivities up to 10" S cm" [201]. A mixture with sulfuric acid or use of tetrabutylammonium tetrafluoroborate as the supporting electrolyte in acetonitrile with the trimer produced no polymer, only gels or powder, respectively [250]. 

Polythiophene has been synthesized chemically by polycondensation reactions of difunctionalized thio-phene derivatives (starting from 2.S-dihalothiophene) as well as by electropolymerization of thiophene itself. One may also start with bithiophene, terthiophene or higher oligomers of thiophene in order to prepare polymers with thiophene systems, but with differing properties, especially with regard to the electrochemical behaviour. 

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