POLY THIOPHENES P T s

The term Poly(thiophenes) (P(T)s) includes direct derivatives such as poly(3-alkyl-thiophenes) (P(3AT)s). Poly(thiophene) was one of the early CPs synthesized, but real interest in this class was augmented with the discovery that 3-substitution of the thiophene ring yielded a wide variety of practically very versatile CPs. 

Nickel-catalyzed polymerization of thiophene. Reference [591], reproduced with permission. 

Other methods employed include the relatively simple direct oxidation with FeClj or Mods (dopant/oxidant) in chloroform and precipitation in MeOH [592], Friedel-Crafts alkylation [87], coupling of the dihalide using Ni catalysts [593] and organocuprate coupling [594]. In their preparation of a series of melt-spinnable long-chain-alI l-3-substituted P(T)s, Yoshino et al. [276] used a simple oxidation with FeClj in chloroform. After 15 h of reaction, the polymer was poured into methanol and washed therewith. 

Zhang and Tour [595] recently described a chemical synthesis of amino/nitro-substituted P(T) derivatives said to possess very low bandgaps. Their synthesis is summarized in Pie. 14-2. The final product, 5 ( (niax)= 662 nm), was purified by dialysis due to its solubility in water, and was said to possess significant zwitter-ionic/quinoidal character. 

Indeed, P(bi-T) on Pt has been used as an independent working electrode for the electrochemical characterization of the FeCPj system [56]. 

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One of the first soluble CPs to be studied in detail were the poly (thiophenes) (P(T) s) substituted at the 3-position with long chain (up to octadeca-) alkyl groups, which rendered them amenable to reproducible solution (i.e. repeated solution/-dissolution) in organic solvents (such as chloroform), and thus processible, in their reduced, de-dopedforms [20,157, 259-261]. The same procedures used for chemical synthesis of P(T) s can be used for these as well, if one starts with the appropriate monomer. For instance, 3-octyl thiophene can be polymerized after iodination at the... 

TAIU.F. 14-1 Illustration of the variation of properties obtainable in 3-substituted poly(thiophenes) (P(T)s) with different substituents R. 

The wide variety of coupling methods adapted from organic synthesis to condensation polymerization of just one CP can be appreciated from Fig. 5-12. for poly(pheny-lene). Typical condensations and eliminations adapted to syntheses of such CPs as poly(phenylene) and poly(phenylene vinylene) (P(PV)) are illustrated in Fig. 5-13. Fig. 5-14 shows the variety of precursor routes available to P(PV). More recently, the Yu group [86] has demonstrated application of Pd-catalyzed Stille and Heck reactions to the synthesis of poly(thiophene) (P(T)) derivatives (cf. Fig. 5-15. Besides the Grignard couplings such as shown in Eq. 1.6, Chapter 1, P(T) s can also be prepared via a variety of other procedures, such as Friedel-Crafts alkylation [87], and direct oxidation with FeClj as for P(Py) above. 

The most well known derivatives of P(T), which are not simply substituted P(T)s, and the only ones discussed in this section, are poly(isothianaphthene) (P(ITN), also called poly(benzo[c] thiophene), its analogue poly(naphtho [c] thiophene), the... 

T. Yamamoto, A. Morita, Y. Miyazaki, T. Marayama, H. Wakayama, Z.H. Zhou, Y. Nakamura, T. Kanbara, S. Sasaki, and K. Kubota, Preparation of ir-conjugated poly(thiophene-2,5-diyl), poly(p-phenylene), and related polymers using zerovalent nickel complexes. Linear structure and properties of the TT-conjugated polymers, Macromolecules, 25 1214—1223, 1992. 

B. Li, G. Sauve, M. C. lovu, M. Jeffries-EL, R. Zhang, J. Cooper, S. Santhanam, L. Schultz, J. C. Revelli, A. G. Kusne, et al. Volatile Organic Compound Detection Using Nanostructured Copolymers. Nano Lett. 2006,6,1598-1602. Q. Zhang, A. Cirpan, T. P. Russell, T. Emrick, Donor-Acceptor Poly(Thiophene-B/ock-Perylene Diimide) Copolymers Synthesis and Solar Cell Fabrication. Macromolecules 2009,42,1079-1082. 

One of the problems associated with PEDOT-PSS is that the exact composition is generally difficult to determine. The blend that is obtained using poly(sodium-p-styrenesulfonate) (PSSNa), either chemically via Fe(III) salts [103] or electrochemically [134], has been investigated by means of energy dispersive x-ray (EDX) analyses, but the results were rather uncertain. The sulfonate/thiophene molar ratio J s/t was found to be in the range of 0.2-3 for samples made chemically [103] and —0.2 for those made electrochemically [134]. The electrical conductivity appears to increase with a decrease of Ps/n with typical values around 1 and 10 S cm for Rs/r = 2.5 and 0.25, respectively [103]. 

P. Andreani, L. Angiolini, D. Caretti, E. Salatelli, Synthesis and polymerization of 3,3"-di [(S)-(-t)-2-methylbutyl]-2,2 5, 2"-terthiophene a new monomer precursor to chiral regioreg-ular poly(thiophene). J. Mater. Chem. 8, 1109-1111 (1998)... 

It is evident that the use of solubilizing groups, such as the long alkyl chains for poly(thiophenes) or the long chain substituents for the P(DiAc) s described above, can render some measure of solubility or melt processibility to CPs. Indeed in one such example, Liu and Gregory [266] describe the chemical polymerization of a 3-urethane-substituted thiophene, to yield a P(T) soluble, albeit only in its de-doped... 

Certain poly(bithiophenes) qualify as P(T) derivatives. Thus, for instance, Ng et al. [620] synthesized homopolymers of the symmetrical 3,3 -dibutylsulfanyl-2,2 -bithiophene (DBSBT) and its copolymers with thiophene and bithiophene via the standard Ni-catalyzed Grignard cross-coupling. CPs with bandgaps int he region of 1.7 to 1.8 eV were obtained. Conductivities with l2-doping were however poor, a maximum of ca. 10 S/cm. Fig. 14-10 summarizes this synthesis. 

Higher hetero-atom analogues of P(PO) and P(PS), viz. P(PSe) and P(PTe), of limited practical utility, have also been synthesized [572, 665, 666]. Conductivities of AsFj doped P(PSe), as an example, are in the 10 S/cm range, while those of P(PTe) are even poorer. More recently, such CPs have seen renewed work. For example, Peulon et al. [667] described a study of the effect of dopant on the electrochemical and physical properties of poly(selenyl thiophene) (P(SeT)), prepared by electropolymerization of the monomer in acetonitrile. They claimed that dopants such as hexafluorophosphate and perchlorate had a stronger influence on CP properties than for P(T) alone. 

R. P. Kingsborough and T. M. Swager. 1999. Poly thiophene hybrids of transition-metal bis(salicylidenimine)s Correlation between structure and electronic properties. 7 Am Chem Soc 121(38) 8825-8834. 

Burgmayer P and Murray R W 1984 Ion Gate Electrodes. Polypyrrole as a switchable ion conductor membrane J. Phys. Chem. 88 2515-21 Otero T F and de Larreta E 1988 Conductivity and capacity of polythiophene films impedance study J. Electroanal. Chem. 244 311-18 Sunde S, Hagen G and Odegird R 1993 Impedance analysis of the electrochemical doping of poly(3-methyl-thiophene) from aqueous nitrate solutions J. Electroanal. Chem. 345 59-82 Zaborsky O R 1973 Immobilized Enzymes (Cleveland, OH Chemical Rubber Company) (see especially pp 69,87)... 

Nguyen, T.P. and de Vos, S.A. (2004) An investigation into the effect of chemical and thermal treatments on the structural changes of poly(3,4-etiiylenedio thiophene) / polystyrenesulfonate and consequences on its use on indium tin oxide substrates. Applied Surface Science, 221, 330-339. 

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