Polythiophene derivatives processability

First, the above-mentioned sensors have major drawbacks, as the detection and recognition event is a function of the nature and characteristics of the side chains, and the side chain functionalization of the CP requires advanced synthesis and extensive purification of numerous monomeric and polymeric derivatives. Second, this generation of sensors primarily employed optical absorption as the source for detection, resulting in lower sensitivity when compared with other sensing systems for biological processes. However, the use of fluorescence detection within these sensing systems could justify continued development. More recent examples include a fluorescent polythiophene derivative with carbohydrate functionalized side chains for the detection of different bacteria [15] and novel synthesis schemes for ligand-functionalization of polythiophenes [16]. 

Closely related to liquid electrolyte dye-sensitized solar cells (DSSCs, also known as Gratzel cells ) [283,284], the class of soHd-state DSSCs has been developed to improve device stability and reduce complications in the production process [285-288]. Thus, although polymers can be utilized as replacements for sensitizing dyes (as in liquid electrolyte DSSCs) [289-291], the main effort in applying conjugated polymers focuses on soHd-state DSSCs [45,292-298]. With environmentally friendly production of this polymer based solid-state DSSC in mind, a device based on water-soluble polythiophene derivative has been presented as well [299]. 

Fig. 3.4. Two advanced polythiophene derivatives with liquid crystal properties. These materials are solution processable and can be processed into relatively large crystal domains through controlled thermal cycling, (a) PQT, where R is an alkane (in PQT-12, for example, R is (CHn)CH3) [21] (b) poly(2,5-bis(3-alkylthiophen-2-yl) thieno[3,2-b]thiophene), where R is also a variable length alkane chain 10-14 C long ([22])...

Leclerc, M., and M. Paid. 1997. Electrical and optical properties of processable polythiophene derivatives Structure-property relathionships. Adv Mflter 9 1087-1094. 

In order to avoid the problems associated with the instability of the n-doping process of the polymer, it has been proposed to replace the n-doped polymer at the negative electrode with a carbon electrode to form the so-called hybrid capacitor [22, 33, 40]. Such hybrid capacitors with a p-doped polythiophene derivative as the positive electrode and activated carbon as the negative electrode were found to outperform double-layer carbon capacitors in terms of specific power while maintaining good performance cyclability over 10000 cycles [40]. Another asymmetric hybrid capacitor has been built using a lithium titanate (Li4Ti50i2) intercalation anode, instead of a carbon electrode and PFPT electrode [35]. 

Unfortunately, PA is very unstable in the ambient atmosphere, both infusible and insoluble, and consequently not easy to process. There are, however, many conductive polymers that are reasonably stable and display high values of conductivity ( 10 S m ). The absence of convenient processibility still remains a problem area, with the exception of PAn and polythiophene derivatives, for the majority of the polymers that are doped to form conductive derivatives. Recent reports [125-127], however, suggest that the presence of flexible substituents in certain polymers can provide solution or melt processability without dramatically decreasing conductivities in the doped state. 

Generally highly electrically conductive materials arising from polythiophene are available from the appropriate polythiophene with processable properties after oxidation with an oxidant in order to produce the oxidized form (p-type doped form) or after reduction with a reductant to produce the reduced form (n-type doped form) of the polymer in the case of chemical preparation. In the case of electrochemical formation of polythiophene or its derivatives starting from thiophene or suitable derivatives automatically the oxidized, neutral or reduced form of the electrically conductive material can be built up. 

The nonlinearity of conjugated polymers was discovered and studied bodi experimentally and theoretically already in the 1970 s [117-119]. Because of the lack of stable and processable materials the research activity then decreased to rise again in recent years with the advent of soluble polydiacetylenes and polythiophene derivatives. 

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