Conducting organic polymers have found two main kinds of application in electronics so far: as materials for construction of various devices and as selective layers in chemical sensors. In either case, interaction with ambient gases is critical. It may compromise the performance of a device based on conducting polymers, whereas it is beneficial in a sensor. Conductivity has been the primary property of interest. Work function--related to conductivity, but in principle a different property--has received only scant attention. Our aim here is to discuss the usability of conducting polymers in both types of electronic applications in light of these two parameters.

Conducting polymers in electronic chemical sensors.

Polymers for chemical sensing

Electrically induced light emission from conjugated organic molecules in a condensed phase has constituted one of the most investigated phenomena in the recent past for a variety of reasons. The considerable development achieved in this field has been mainly based on the search of new configurations for luminescent devices such as flexible large area light-emitting diodes, and in the synthesis of improved light-emitting organic materials. In the present review a particular aspect of electrically induced light-emission phenomena from organic materials is considered, namely, organic electrochemiluminescence, which is the phenomenon of light emission from excited organic molecules generated upon occurrence of electrochemically driven redox reactions. Such processes can produce luminescence in the visible range if the resulting oxidized/reduced forms of the conjugated organic molecules form excited species capable of emitting photons within the energy range 1.5−3.5 eV. Electrochemiluminescence from organic em...

Electrochemiluminescence from Organic Emitters

Thirty Years of CHEMFETs – A Personal View

Electrochemical adjustment of the work function of a conducting polymer

Structural and electronic transitions in poly(phenylenesulfide phenyleneamine) (PPSA) upon electrochemical doping have been investigated. The results indicate that polarons are the predominant charge defects at low doping levels, yielding an electronically and mechanically stable material. The electrochemical doping at high potentials induces a transition of the polarons to a bipolaron state. Due to the heterogeneous nature of the polymer chain and different oxidation potentials associated with aniline and phenylene sulfide units, the formation of polaron and bipolaron is distinguished as two separated steps. The dopant perchlorate ion exists in the polymer matrix, not only as charge neutralizer but also as a ligand that is simultaneously Coulombically bound to the positively charged S or N sites on one polymer chain and hydrogen bonded to the N−H group on the neighboring chain. The formation of such perchlorate anion centered Coulombic/hydrogen-bonded complexes has a major impact on the electrochemical a...

Structural, Electronic, and Morphological Changes in Poly(phenylenesulfide Phenyleneamine) Upon Electrochemical Doping

Electrochemical modulation of the electronic properties in conducting poly(phenylenesulfidephenyleneamine)

Structural and electronic transitions in poly(thiophenyleneiminophenylene), usually referred to as poly(phenylenesulfidephenyleneamine) (PPSA) upon electrochemical doping with LiClO4 have been investigated. The unusual electrochemical behavior of PPSA indicates that the dopant anions are bound in two energetically different sites. In the so-called "binding site", the ClO4- anion is Coulombically attracted to the positively charged S or N sites on one chain and simultaneously hydrogen-bonded with the N-H group on a neighboring polymer chain. This strong interaction causes a re-organization of the polymer chains, resulting in the formation of a networked structure linked together by these ClO4- Coulombic/hydrogen bonding "bridges". However, in the "non-binding site", the ClO4- anion is very weakly bound, involves only the electrostatic interaction and can be reversibly exchanged when the doped polymer is reduced. In the repeated cycling, the continuous and alternating influx and expulsion of ClO4- ions serves as a self-organizing process for such networked structures, giving rise to a diminishing number of available "non-binding" sites. The occurrence of these ordered structures has a major impact on the electrochemical activity and the morphology of the doped polymer. Also due to stabilization of the dopant ions, the doped polymer can be kept in a stable and desirable oxidation state, thus both work function and conductivity of the polymer can be electrochemically controlled.

Tuning of Electronic Properties in Conducting Polymers

The ClO 4 -doped poly(phenylenesulfidephenyleneamine) (PPSA) was electrochemically prepared and investigated with cyclic and square-wave voltammetry (SWV). The unusual electrochemical behavior of PPSA indicates that the dopant ClO 4 anions are bound in two energetically different sites. In the so-called binding site, the ClO 4 anion is coulombically attracted to the positively charged S or N sites on one chain and simultancously hydrogen bonded with the N-H group on a neighboring polymer chain. This strong interaction causes a reorganization of the polymer chains upon cycling in 0.2 M LiClO 4 /acetonitrile, resulting in the formation of a networked structure linked together by these ClO 4 coulombic/hydrogen bonding bridges. However, in the nonbinding site, the ClO 4 anion is very weakly bound, involves only the electrostatic interaction, and can be reversibly exchanged when the doped polymer is reduced, The use of SWV also allows us to differentiate between these two types of sites in the bulk and at the surface.

Guofeng Li

Papers

Structural, Electronic, and Morphological Changes in Poly(phenylenesulfide Phenyleneamine) Upon Electrochemical Doping

Electrochemical modulation of the electronic properties in conducting poly(phenylenesulfidephenyleneamine)

Tuning of Electronic Properties in Conducting Polymers

Square-Wave Voltammetry of ClO4 − -Doped Poly(phenylenesulfidephenyleneamine)