Applications
A number of applications have been proposed for conducting PTs, but none has been commercialized. Potential applications include field-effect transistors, electroluminescent devices, solar cells, photochemical resists, nonlinear optic devices, batteries, diodes, and chemical sensors. In general, there are two categories of applications for conducting polymers. Static applications rely upon the intrinsic conductivity of the materials, combined with their ease of processing and material properties common to polymeric materials. Dynamic applications utilize changes in the conductive and optical properties, resulting either from application of electric potentials or from environmental stimuli.
As an example of a static application, poly(3,4-ethylenedioxythiophene)-poly(styrene sulfonate) (PEDOT-PSS) product Clevios P (Figure 7) from Heraeus has been extensively used as an antistatic coating (as packaging materials for electronic components, for example). AGFA coats 200 m × 10 m of photographic film per year with PEDOT:PSS because of its antistatic properties. The thin layer of PEDOT:PSS is virtually transparent and colorless, prevents electrostatic discharges during film rewinding, and reduces dust buildup on the negatives after processing.
PEDOT can also be used in dynamic applications where a potential is applied to a polymer film. The electrochromic properties of PEDOT are used to manufacture windows and mirrors which can become opaque or reflective upon the application of an electric potential. Widespread adoption of electrochromic windows could save billions of dollars per year in air conditioning costs. Finally, Phillips has commercialized a mobile phone with an electrically switchable PEDOT mirror.
The use of PTs as sensors responding to an analyte has also been the subject of intense research. In addition to biosensor applications, PTs can also be functionalized with synthetic receptors for detecting metal ions or chiral molecules as well. PTs with pendant and main-chain crown ether functionalities were reported in 1993 by the research groups of Bäuerle and Swager, respectively (Figure 8). Electrochemically polymerized thin films of the Bäuerle pendant crown ether PT were exposed to millimolar concentrations of alkali cations (Li, Na, and K). The current which passed through the film at a fixed potential dropped dramatically in lithium ion solutions, less so for sodium ion solutions, and only slightly for potassium ion solutions. The Swager main chain crown ether PTs were prepared by chemical coupling and characterized by absorbance spectroscopy. Addition of the same alkali cations resulted in absorbance shifts of 46 nm (Li), 91 nm (Na), and 22 nm (K). The size of the shifts corresponds to the ion-binding preferences of the corresponding crown ether, resulting from a twist in the conjugated polymer backbone induced by ion binding.
In the course of their studies of the optical properties of chiral PTs, Yashima and Goto found that a PT with a chiral primary amine (Figure 9) was sensitive to chiral amino alcohols, producing mirror-image-split ICD responses in the π–transition region. This was the first example of chiral recognition by PTs using a chiral detection method (CD spectroscopy). This distinguished it from earlier work by Lemaire et al. who used an achiral detection method (cyclic voltammetry) to detect incorporation of chiral dopant anions into an electrochemically polymerized chiral PT.
A fluorine substituted polythiophene was shown to yield 7% efficiency in polymer-fullerene solar cells.
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