Electronically conducting polymer redox switching

FIGURE 18.2 Typical cyclic voltammetry (CV) corresponding to redox switching of electronically conducting polymers (ECPs). 

In this section we examine the mechanism of potential induced redox switching in electronically conducting polymer Aims. The term redox switching refers to the transition from an electronically insulating to an... 

At the simplest level, communication with amino acids, proteins, enzymes, antibodies, DNA, and whole cells is clearly important [158]. It is well known that biological systems can be influenced by the application of electric fields. The ICP provides us with the capability of charge injection or removal at biological interfaces due to its electronic conductivity. More interestingly, though is the redox capability of these polymers, whereby they can function as simple on-o f switches, facilitate controlled release of molecular species of interest, or direct mechanical interaction with the biological interface in the form of actuation. 

All conducting polymers are potentially electrochromic in thin-film form, redox switching giving rise to new optical absorption bands in accompaniment with simultaneous transport of electronic charge and counter ions in the polymer matrix, p-doping shifts the optical absorption band towards the lower energy... 

Metallophthalocyanine polymers offer good stability in thermal, chemical, hydrolytic and photochemical environments. The reversible redox property and cycle stability of phthalocyanine compounds and their polymers make them useful as active components in sensors, switches, diodes, memory devices, NLO materials, etc. different types of phthalocyanine polymers are available and they are amenable to chemical modifications to suit the devices requirements. It is possible to exercise chemical control of the properties of the phthalocyanine polymers as well as functionalize other conducting polymers with the characteristics of phthalocyanines. Hence phthalocyanine polymers have become potential candidates for producing useful and viable materials for electronic, optoelectronic and molecular electronic applications. 

Both the transition between a hydrophobic and a hydrophilic state (see above) and the high electronic conductivity of the conjugated conducting polymers lead to considerable practical differences in the dynamics of redox switching between these systems and redox polymers. 

Redox switches are threshold sensor devices in which the electroconductive polymer is rendered conducting (turned on) under one set of conditions and insulating (turned off) under another. The sharp and rapid change in electrical conductivity through a well-defined resistance transition is essential to the performance of a redox switch. More aptly described as electronic devices, redox switches may be rendered chemically or biologically specific and may be used as simple on/off chemical indicator devices. 

The poly(I)-based transistor is the first illustration of a microelectrochemical transistor based on a combination of a conducting and a conventional redox polymer as the active material. The transistor "turns on" at VG corresponding to oxidation of the polythiophene backbone. The resistivity of poly(I) declines by a factor of 105 upon changing VG from 0.4 V to 0.8 V vs. Ag+/Ag. When Vg is moved close to the one-electron reduction potential of V2+/+, the conventional redox conductivity gives a small degree of "turn on". A sharp Iq-Vq characteristic results, with an Ip(peak) at Vq = E° (V2+/+). Though the microelectrochemical devices based on conventional redox conduction have both slow switching speed and a... 

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