Substituted Polythiophenes

The phenomenon is found with many, but not all substituted polythiophenes. Studies of 3,3 -di-alkyl-substituted polythiophenes revealed no temperature-induced colour change [17]. But many other structures will give thermochromism and solvatochromism. Polythiophenes substituted both with alkoxy and alkyl side chains may show it both purely amorphous and partially crystalline polythiophenes show it short and long-chain polymers may show it both regular and irregular polymers show it (see Figure 15.1),... 

Polythiophenes substituted regioregularly with alkyl chains were prepared by the polymerization of alkylated bithiophenes and terthiophene. Souto et al. polymerized 3,3 -dihexyl-2,2 -bithiophene (41) with iron(III)... 

The doping- and photoinduced absorption spectra of polythiophene, substituted polythiophenes, and their composites have been reported [145-166]. Let us discuss the subgap absorptions due to charged excitations in unsubstituted polythiophene. The optical absorption spectrum of BF -doped polythiophene [42,46] and the photoinduced absorption spectrum of polythiophene [145] are shown in Figure 20. In the spectrum of BFJ -doped polythiophene (Fig. 20a), doping-induced bands are observed at 0.73 and 1.68 eV, which are located below the gap edge, 1.94 eV. The 0.73-... 

TTie assignments of the doping- and photoinduced absorption bands of polythiophene, substituted polythiophenes, and their... 

Polythiophene can be synthesized by electrochemical polymerization or chemical oxidation of the monomer. A large number of substituted polythiophenes have been prepared, with the properties of the polymer depending on the nature of the substituent group. Oligomers of polythiophene such as (a-sexithienyl thiophene) can be prepared by oxidative linking of smaller thiophene units (33). These oligomers can be sublimed in vacuum to create polymer thin films for use in organic-based transistors. 

In all cases of electrochemicaHy or chemically polymerized unsubstituted polypyrrole, the final polymer is intractable in both the conducting and insulating forms. In contrast, a broad number of substituted polythiophenes have been found to be processible both from solution and in the melt. The most studied of these systems ate the poly(3-alkylthiophenes) (P3AT). 

Polythiophenes with substituents other than alkyl groups at the 3 position have been prepared by the polymerization of substituted monomers. Many of these polymers have been substituted alkylthiophenes (8) where example side chains are (R =) —(86—89), —OCH (68), —NHC(0) (CH2) qCH (6 )) —0502(0112)30112 (90). Ohiral side chains have also been employed (91,92). Poly(3-alkoxythiophenes) (9) (93—95) and... 

Polythiophene [78] is a promising material for certain future electronic applications, due to its relatively high stability and processability in the substituted form [79-81]. Upon substitution, with e.g. alkyl side-chains [79, 80], polythiophene exhibit properties such as solvalochromism [82] and thermochromism [83]. Presently, a large variety of substituted polythiophenes with various band gaps exists (for example see Ref. [81 ]). 

Many substituted thiophenes have also been electrochemically polymerised [19,54,399-405] (Table 4) as have thiophene dimers [21,37,55,251,400,406], trimers [21, 83,407], and tetramers [256,406], with the thiophene dimer giving rise to higher quality films than does the monomer [37, 395,408]. Several polycyclic monomers including a thiophene ring have also been polymerised [408-416], as have a series of compounds consisting of two thiophene rings linked by a polyene chain (Fig. 23c). The polymerisation of dithieno-thiophene (Fig. 23d) results in a polymer which shows remarkable similarity to polythiophene in its properties [409,410,414],... 

Several other organoboron polymers have been developed by various synthetic strategies and utilized to construct polymeric sensing systems for cations, dopamine, saccharides, and so on. Fabre and co-workers have reported the preparation of a conjugated trifluoroborate-substituted polythiophene system for sensing cations such as... 

Figure 16 Trifluoroborate-substituted thiophene monomer (22) used in the synthesis of a conjugated polythiophene system. (Adapted from ref. 41.)...

Compound 45 incorporates a fullerene acceptor and two substituted polythiophene-ethenyl tails it rectifies as an LS monolayer. Interestingly, it rectifies in one direction for smaller biases between 0 and 2.0 V, but in the reverse direction at higher biases, perhaps indicating a change in conduction mechanism, as discussed above. It also rectifies between A1 and Pb electrodes at 4.2 K (Fig. 22a) [108],... 

M.R. Andersson, O. Thomas, W. Mammo, M. Svensson, M. Theander, and O. Inganas, Substituted polythiophenes designed for optoelectronic devices and conductors, J. Mater. Chem., 9 1933-1940, 1999. 

M. Berggren, G. Gustaffson, O. Inganas, M.R. Andersson, O. Wennerstrom, and T. Hjertberg, Thermal control of near-infrared and visible electroluminescence in alkyl-phenyl substituted polythiophenes, Appl. Phys. Lett., 65 1489-1491, 1994. 

T. Johansson, W. Mammo, M.R. Andersson, and O. Inganas, Light-emitting electrochemical cells from oligo(ethylene oxidej-substituted polythiophenes evidence for in situ doping, Chem. Mater., 11 3133-3139, 1999. 

P Dyreklev, M Berggren, O Inganas, MR Andersson, O Wennerstrom, and T Hjertberg, Polarized electroluminescence from an oriented substituted polythiophene in a light emitting diode, Adv. Mater., 7 43-45, 1995. 

Such color transitions were illustrated by Leclerc and coworkers via temperature changes in the case of a substituted polythiophene (Fig. 3). 

Le Bouch N, Auger M, Leclerc M (2008) Structure and segmental motions in a substituted polythiophene a solid-state NMR study. Macromol Chem Phys 209 2455-2462... 

The other important electrochromic polymers are the polypyrroles and polythiophenes, obtained by polymerisation of the parent pyrrole and thiophene or, more importantly, their 3,4-substituted derivatives. The most widely studied of these two classes of polymers in electrochromic outlets are the poly thiophenes, which are readily synthesised by the reaction of the substituted monomer with FeClj in chloroform solution. The colour change properties of a variety of poly thiophenes in the presence of a counter-ion are shown in Table 1.14. ... 

Many other polymeric systems are of interest in polymer LEDs. Polythiophenes have been known for some time but it was not until improved synthetic methods were developed that their potential was realised. The process involves the reaction of the substituted monomer with FeClj in chloroform solution. After polymerisation has occurred the product precipitates and is isolated and washed. Further special purification methods are required to obtain satisfactorily pure materials. One product, of commercial interest, developed by Bayer is poly(ethylenedioxy)thiophene, known as PEDOT (3.110). This product when doped with polystyrene sulfonate, sold as Baytron P, has been found to be effective as a conducting, hole-injecting layer on the ITO electrode. ... 

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