Editing Conductive polymer

{{Short description|Organic polymers that conduct electricity}}
{{about|bulk applications of conductive polymers|single-molecule electronics|Molecular scale electronics}}

[[File:ConductivePoly.png|400px|thumb|Chemical structures of some conductive polymers. From top left clockwise: [[polyacetylene]]; [[Poly(p-phenylene vinylene)|polyphenylene vinylene]]; [[polypyrrole]] (X = NH) and [[polythiophene]] (X = S); and [[polyaniline]] (X = NH) and [[Poly(p-phenylene sulfide)|polyphenylene sulfide]] (X = S).]]

'''Conductive polymers''' or, more precisely, '''intrinsically conducting polymers (ICPs)''' are [[organic polymer]]s that [[Electrical conductance|conduct]] [[electricity]].<ref name="Inzelt-introduction">{{ cite book | series = Monographs in Electrochemistry | title = Conducting Polymers: A New Era in Electrochemistry | first = György | last = Inzelt | editor-first = F. | editor-last = Scholz | publisher = Springer | date = 2008 | pages = 1–6 | chapter = Chapter 1: Introduction | isbn = 978-3-540-75929-4 | chapter-url = https://books.google.com/books?id=4rFDAzo5lPQC&pg=PA264}}</ref><ref>Conducting Polymers, Editor: Toribio Fernandez Otero, Royal Society of Chemistry, Cambridge 2016, https://pubs.rsc.org/en/content/ebook/978-1-78262-374-8</ref> Such compounds may have metallic conductivity or can be [[semiconductor]]s. The main advantage of conductive polymers is that they are easy to process, mainly by [[Dispersion (chemistry)|dispersion]]. Conductive polymers are generally not [[thermoplastic]]s, ''i.e.'', they are not thermoformable. But, like insulating polymers, they are organic materials. They can offer high electrical conductivity but do not show similar mechanical properties to other commercially available polymers. The electrical properties can be fine-tuned using the methods of [[organic synthesis]]<ref name=Ullmann>{{cite book | doi = 10.1002/14356007.a21_429 | chapter = Polymers, Electrically Conducting | title = Ullmann's Encyclopedia of Industrial Chemistry | date = 2000 | last1 = Naarmann | first1 = Herbert | isbn = 3527306730}}</ref> and by advanced dispersion techniques.<ref name=nalwa/>

==History==
Polyaniline was first described in the mid-19th century by [[Henry Letheby]], who investigated the electrochemical and chemical oxidation products of aniline in acidic media. He noted that the reduced form was colourless but the oxidized forms were deep blue.<ref name="Inzelt-history">{{cite book | series = Monographs in Electrochemistry | title = Conducting Polymers: A New Era in Electrochemistry | first = György | last = Inzelt | editor-first = F. | editor-last = Scholz | publisher = [[Springer Science+Business Media|Springer]] | date = 2008 | pages = 265–267 | chapter = Chapter 8: Historical Background (Or: There Is Nothing New Under the Sun) | isbn = 978-3-540-75929-4 | chapter-url = https://books.google.com/books?id=4rFDAzo5lPQC&pg=PA264}}</ref>

The first highly-conductive organic compounds were the [[charge transfer complex]]es.<ref name="firsthalfcentury">{{cite journal|doi=10.1196/annals.1292.016|title=An Overview of the First Half-Century of Molecular Electronics|date=2003|last1=Hush|first1=Noel S.|journal=Annals of the New York Academy of Sciences|volume=1006|issue=1|pmid=14976006|bibcode=2003NYASA1006....1H|pages=1–20|s2cid=24968273}}</ref> In the 1950s, researchers reported that polycyclic aromatic compounds formed semi-conducting charge-transfer complex salts with halogens.<ref name=Ullmann/> In 1954, researchers at Bell Labs and elsewhere reported organic charge transfer complexes with [[resistivities]] as low as 8 [[Ohm|Ω]].cm.<ref name=Okamoto/><ref>{{cite journal | doi = 10.1038/173168a0 | title = Electrical Conductivity of the Perylene–Bromine Complex | date = 1954 | last1 = Akamatu | first1 = Hideo | last2 = Inokuchi | first2 = Hiroo | last3 = Matsunaga | first3 = Yoshio | journal = Nature | volume = 173 | issue = 4395 | pages = 168–169|bibcode = 1954Natur.173..168A | s2cid = 4275335 }}</ref> In the early 1970s, researchers demonstrated salts of [[tetrathiafulvalene]] show<ref name="UTD">{{cite journal|doi=10.1021/ja00784a066|title=Electron transfer in a new highly conducting donor-acceptor complex|date=1973|last1=Ferraris|first1=JohnS|journal=Journal of the American Chemical Society|volume=95|pages=948–949|last2=Cowan|first2=D. O.|last3=Walatka|first3=V.|last4=Perlstein|first4=J. H.|issue=3|bibcode=1973JAChS..95..948F }}</ref> almost metallic conductivity, while superconductivity was demonstrated in 1980. Broad research on salts of charge transfer complexes continues today. While these compounds were technically not polymers, this indicated that organic compounds can carry current. While organic conductors were previously intermittently discussed, the field was particularly energized by the prediction of [[superconductivity]]<ref>{{cite journal|doi=10.1103/PhysRev.134.A1416|title=Possibility of Synthesizing an Organic Superconductor|date=1964|last1=Little|first1=W. A.|journal=Physical Review|volume=134|pages=A1416–A1424|issue=6A|bibcode = 1964PhRv..134.1416L }}</ref> following the discovery of [[BCS theory]].

In 1963 Australians B.A. Bolto, D.E. Weiss, and coworkers reported derivatives of [[polypyrrole]] with resistivities as low as 1 Ω.cm. There have been multiple reports of similar high-conductivity oxidized polyacetylenes.<ref>{{cite journal|url=http://www.drproctor.com/os/weisspaper.pdf|author1=Bolto, B.A. |author2=McNeill, R. |author3=Weiss, D.E.  |title=Electronic Conduction in Polymers. III. Electronic Properties of Polypyrrole|journal= Australian Journal of Chemistry |volume=16|issue=6|pages=1090|year= 1963|doi=10.1071/ch9631090}}</ref><ref name=Okamoto>Okamoto, Yoshikuko and Brenner, Walter (1964) "Polymers", Ch. 7, pp. 125–158 in ''Organic Semiconductors''. Reinhold</ref> With the notable exception of [[charge transfer complex]]es (some of which are even [[superconductor]]s), organic molecules were previously considered insulators or at best weakly conducting [[semiconductors]]. Subsequently, DeSurville and coworkers reported high conductivity in a polyaniline.<ref>{{cite journal|doi=10.1016/0013-4686(68)80071-4|title=Electrochemical chains using protolytic organic semiconductors|date=1968|last1=De Surville|first1=R.|last2=Jozefowicz|first2=M.|last3=Yu|first3=L.T.|last4=Pepichon|first4=J.|last5=Buvet|first5=R.|journal=Electrochimica Acta|volume=13|pages=1451–1458|issue=6}}</ref> Likewise, in 1980, Diaz and Logan reported films of polyaniline that can serve as electrodes.<ref>{{cite journal|doi=10.1016/S0022-0728(80)80081-7|title=Electroactive polyaniline films|date=1980|last1=Diaz|first1=A|last2=Logan|first2=J|journal=Journal of Electroanalytical Chemistry|volume=111|pages=111–114}}</ref>

While mostly operating at the scale of less than 100 nanometers, "molecular" electronic processes can collectively manifest on a macro scale. Examples include [[quantum tunneling]], [[negative resistance]], [[phonon]]-assisted hopping and [[polaron]]s. In 1977, [[Alan J. Heeger]], [[Alan MacDiarmid]] and [[Hideki Shirakawa]] reported similar high conductivity in oxidized iodine-doped polyacetylene.<ref>{{Cite journal|doi=10.1039/C39770000578|title=Synthesis of electrically conducting organic polymers: Halogen derivatives of polyacetylene, (CH) x|date=1977|last1=Shirakawa|first1=Hideki|last2=Louis|first2=Edwin J.|last3=MacDiarmid|first3=Alan G.|last4=Chiang|first4=Chwan K.|last5=Heeger|first5=Alan J.|journal=Journal of the Chemical Society, Chemical Communications|issue=16|page=578|url=https://apps.dtic.mil/sti/pdfs/ADA041866.pdf|access-date=2018-04-29|archive-date=2017-09-25|archive-url=https://web.archive.org/web/20170925014126/http://www.dtic.mil/get-tr-doc/pdf?AD=ADA041866|url-status=live}}</ref> For this research, they were awarded the 2000 [[Nobel Prize in Chemistry]] ''"for the discovery and development of conductive polymers."''<ref name="nobel">{{cite web| url=http://nobelprize.org/nobel_prizes/chemistry/laureates/2000/index.html | title=The Nobel Prize in Chemistry 2000 | access-date=2009-06-02}}</ref> Polyacetylene itself did not find practical applications, but drew the attention of scientists and encouraged the rapid growth of the field.<ref name="Inzelt-history" /> Since the late 1980s, [[OLED|organic light-emitting diodes]] (OLEDs) have emerged as an important application of conducting polymers.<ref name="ReferenceA"/><ref>{{ cite journal | title = Electroluminescence in conjugated polymers | journal = Nature | volume = 397 | pages = 121–128 | date = 1999 | doi = 10.1038/16393 |bibcode = 1999Natur.397..121F | issue = 6715 | last1 = Friend | first1 = R. H. | last2 = Gymer | first2 = R. W. | last3 = Holmes | first3 = A. B. | last4 = Burroughes | first4 = J. H. | last5 = Marks | first5 = R. N. | last6 = Taliani | first6 = C. | last7 = Bradley | first7 = D. D. C. | last8 = Santos | first8 = D. A. Dos | last9 = Brdas | first9 = J. L. | last10 = Lgdlund | first10 = M. | last11 = Salaneck | first11 = W. R. | s2cid = 4328634 }}</ref>

==Types==
Linear-backbone "polymer blacks" ([[polyacetylene]], [[polypyrrole]], polyindole and [[polyaniline]]) and their copolymers are the main class of conductive polymers. [[Poly(p-phenylene vinylene)]] (PPV) and its soluble derivatives have emerged as the prototypical [[electroluminescent]] semiconducting polymers. Today, poly(3-alkylthiophenes) are the archetypical materials for [[Solar cell#Organic/polymer solar cells|solar cell]]s and transistors.<ref name=Ullmann/>

The following table presents some organic conductive polymers according to their composition. '''The well-studied classes are written in bold''' and ''the less well studied ones are in italic''.

{| class="wikitable"
|-
! rowspan=2|The main chain contains !! rowspan="2" |No heteroatom
! colspan="2" |[[Heteroatoms]] present
|-
![[Amine|Nitrogen-containing]] !! [[Sulfur]]-containing
|-
| Aromatic cycles
|
* ''[[Polyfluorene|Poly(fluorene)s]]''
* ''poly[[phenylene]]s''
* ''poly[[pyrene]]s''
* ''poly[[azulene]]s''
* ''poly[[naphthalene]]s''
* ''poly[[benzodifurandione]]s''
| The N is in the aromatic cycle:
* '''[[polypyrrole|poly(pyrrole)s]] (PPY)'''
* ''poly[[carbazole]]s''
* ''poly[[indole]]s''
* ''poly[[azepine]]s''
The N is outside the aromatic cycle:
* '''[[polyaniline]]s (PANI)'''
| The S is in the aromatic cycle:
* '''[[polythiophene|poly(thiophene)s]] (PT)'''
* '''[[poly(3,4-ethylenedioxythiophene)]] (PEDOT)'''
The S is outside the aromatic cycle:
* '''[[poly(p-phenylene sulfide)]] (PPS)'''
|-
| Double bonds
|
* '''[[polyacetylene|Poly(acetylene)s]] (PAC)'''
|
|
|-
| Aromatic cycles and double bonds
|
* '''[[Poly(p-phenylene vinylene)]] (PPV)'''
|
|
|}

==Synthesis==
Conductive polymers are prepared by many methods. Most conductive polymers are prepared by oxidative coupling of monocyclic precursors. Such reactions entail [[dehydrogenation]]:
:n H–[X]–H <math>\;\rightarrow\;</math> H–[X]<sub>n</sub>–H + 2(n–1) H<sup>+</sup> + 2(n–1) e<sup>−</sup>
The low [[solubility]] of most polymers presents challenges. Some researchers add solubilizing functional groups to some or all monomers to increase solubility. Others address this through the formation of nanostructures and surfactant-stabilized conducting polymer dispersions in water. These include [[polyaniline nanofibers]] and [[Poly(3,4-ethylenedioxythiophene)|PEDOT]]:[[Sodium polystyrene sulfonate|PSS]]. In many cases, the molecular weights of conductive polymers are lower than conventional [[polymer]]s such as polyethylene. However, in some cases, the [[molecular weight]] need not be high to achieve the desired properties.

There are two main methods used to synthesize conductive polymers, [[chemical synthesis]] and electro (co)polymerization. The [[organic synthesis|chemical synthesis]] means connecting carbon-carbon bond of monomers by placing the simple monomers under various condition, such as heating, pressing, light exposure and catalyst. The advantage is high yield. However, there are many plausible [[Chemical impurity|impurities]] in the end product. The electro (co)polymerization means inserting three electrodes (reference electrode, counter electrode and working electrode) into [[Solution (chemistry)|solution]] including reactors or monomers. By applying voltage to electrodes, redox reaction to synthesize polymer is promoted. Electro (co)polymerization can also be divided into [[Cyclic Voltammetry|Cyclic voltammetry]] and Potentiostatic method by applying cyclic voltage<ref>{{cite journal | last1 = Kesik | first1 = M. | last2 = Akbulut | first2 = H. | last3 = Soylemez | first3 = S. | year = 2014 | title = Synthesis and characterization of conducting polymers containing polypeptide and [[ferrocene]] side chains as ethanol biosensors | journal = Polym. Chem. | volume = 5 | issue = 21| pages = 6295–6306 | doi = 10.1039/c4py00850b }}</ref> and constant voltage, respectively. The advantage of Electro (co)polymerization are the high purity of products. But the method can only synthesize a few products at a time.

==Molecular basis of electrical conductivity==
The conductivity of such polymers is the result of several processes. For example, in traditional polymers such as [[polyethylene]]s, the valence electrons are bound in sp<sup>3</sup> hybridized [[covalent bond]]s. Such "sigma-bonding electrons" have low mobility and do not contribute to the electrical conductivity of the material. However, in [[Conjugated system|conjugated]] materials, the situation is completely different. Conducting polymers have backbones of contiguous sp<sup>2</sup> [[Hybridized orbital|hybridized]] carbon centers. One valence electron on each center resides in a p<sub>z</sub> orbital, which is orthogonal to the other three sigma-bonds. All the p<sub>z</sub> orbitals combine with each other to a molecule wide delocalized set of orbitals. The electrons in these delocalized orbitals have high mobility when the material is "doped" by oxidation, which removes some of these delocalized electrons. Thus, the [[Conjugated system|conjugated p-orbitals]] form a one-dimensional [[electronic band structure|electronic band]], and the electrons within this band become mobile when it is partially emptied. The band structures of conductive polymers can easily be calculated with a [[Tight binding|tight binding model]]. In principle, these same materials can be doped by reduction, which adds electrons to an otherwise unfilled band. In practice, most organic conductors are doped oxidatively to give p-type materials. The redox doping of organic conductors is analogous to the doping of silicon semiconductors, whereby a small fraction of silicon atoms are replaced by electron-rich, ''e.g.'', [[phosphorus]], or electron-poor, ''e.g.'', [[boron]], atoms to create [[n-type semiconductor|n-type]] and [[p-type semiconductor]]s, respectively.

Although typically "doping" conductive polymers involves oxidizing or reducing the material, conductive organic polymers associated with a [[protic solvent]] may also be "self-doped."

Undoped conjugated polymers are semiconductors or insulators. In such compounds, the energy gap can be > 2 eV, which is too great for thermally activated conduction. Therefore, undoped conjugated polymers, such as polythiophenes, [[polyacetylene]]s only have a low electrical conductivity of around 10<sup>−10</sup> to 10<sup>−8</sup> [[Siemens (unit)|S]]/cm. Even at a very low level of doping (< 1%), electrical conductivity increases several orders of magnitude up to values of around 0.1 S/cm. Subsequent doping of the conducting polymers will result in a saturation of the conductivity at values around 0.1–10 kS/cm (10–1000 S/m) for different polymers. Highest values reported up to now are for the conductivity of stretch oriented polyacetylene with confirmed values of about 80 kS/cm (8 MS/m).<ref name="ReferenceA">{{cite journal |doi= 10.1038/347539a0 |title=Light-emitting diodes based on conjugated polymers|date=1990|last1=Burroughes|first1=J. H.|last2= Bradley|first2=D. D. C.|last3=Brown|first3=A. R.|last4=Marks|first4=R. N.|last5=MacKay|first5=K.|last6=Friend|first6=R. H. |last7=Burns|first7=P. L.|last8=Holmes|first8=A. B.|journal=Nature|volume=347|pages=539–541|issue=6293|bibcode=1990Natur.347..539B|s2cid=43158308}}</ref><ref>{{cite journal|doi=10.1103/RevModPhys.60.781|title=Solitons in conducting polymers|date=1988|last1=Heeger|first1=A. J.|last2=Schrieffer|first2=J. R.|last3=Su|first3=W. -P.|journal=Reviews of Modern Physics|volume=60|pages=781–850|last4= Su |first4= W.|bibcode=1988RvMP...60..781H|issue=3}}</ref><ref>{{cite book|last=Heeger|first= A. J.|chapter = Nature of the primary photo-excitations in poly(arylene-vinylenes): Bound neutral excitons or charged polaron pairs|title=  Primary photoexcitations in conjugated polymers: Molecular excitons versus semiconductor band model|editor-link=Niyazi Serdar Sarıçiftçi|editor-last =Sarıçiftçi|editor-first = N. S.|publisher = World Scientific|location= Singapore|date = 1998|isbn=9789814518215|chapter-url = https://books.google.com/books?id=U5jsCgAAQBAJ&pg=PA20}}</ref><ref>Handbook of Organic Conductive Molecules and Polymers; Vol. 1–4, edited by H.S. Nalwa (John Wiley & Sons Ltd., Chichester, 1997).</ref><ref name=h1>{{cite book|title=Handbook of Conducting Polymers|volume=1,2| editor1= Skotheim, T.A.|editor2=Elsenbaumer, R.L.|editor3=Reynolds, J.R. |publisher=Marcel Dekker|place=New York|year= 1998}}</ref><ref>{{cite journal|doi=10.1126/science.258.5087.1474|title=Photoinduced Electron Transfer from a Conducting Polymer to Buckminsterfullerene |date=1992|last1=Sariciftci|first1=N. S.|last2=Smilowitz|first2=L.|last3=Heeger|first3=A. J. |last4= Wudl|first4=F.|journal=Science|volume=258|pmid=17755110|issue=5087|pages=1474–6|bibcode = 1992Sci...258.1474S |s2cid=44646344 }}</ref><ref>{{cite journal|doi=10.1002/adma.200501152|title=Device Physics of Solution-Processed Organic Field-Effect Transistors|date=2005 |last1= Sirringhaus|first1=H.|journal=Advanced Materials|volume=17|pages=2411–2425|issue=20|bibcode=2005AdM....17.2411S | s2cid=10232884 }}</ref>{{Excessive citations inline|date=March 2023}} Although the pi-electrons in polyacetylene are delocalized along the chain, pristine polyacetylene is not a metal. Polyacetylene has alternating single and double bonds which have lengths of 1.44 and 1.36 Å, respectively.<ref>{{cite journal|doi=10.1103/PhysRevLett.51.1191|title=Molecular Geometry of cis- and trans-Polyacetylene by Nutation NMR Spectroscopy|date=1983|last1=Yannoni|first1=C. S.|last2=Clarke|first2=T. C.|journal=Physical Review Letters|volume=51|pages=1191–1193|bibcode=1983PhRvL..51.1191Y|issue=13}}</ref> Upon doping, the bond alteration is diminished in conductivity increases. Non-doping increases in conductivity can also be accomplished in a [[field effect transistor]] (organic FET or [[OFET]]) and by [[photoconductivity|irradiation]]. Some materials also exhibit [[negative differential resistance]] and voltage-controlled "switching" analogous to that seen in inorganic amorphous semiconductors.

Despite intensive research, the relationship between morphology, chain structure and conductivity is still poorly understood.<ref name=h1/> Generally, it is assumed that conductivity should be higher for the higher degree of crystallinity and better alignment of the chains, however this could not be confirmed for [[polyaniline]]<ref>{{Cite journal |last=Wessling |first=Bernhard |date=2010-12-17 |title=New Insight into Organic Metal Polyaniline Morphology and Structure |journal=Polymers |language=en |volume=2 |issue=4 |pages=786–798 |doi=10.3390/polym2040786 |doi-access=free |issn=2073-4360}}</ref> and was only recently confirmed for [[Poly(3,4-ethylenedioxythiophene)|PEDOT]],<ref>{{cite journal | title = ''In situ'' studies of strain dependent transport properties of conducting polymers on elastomeric substrates | last1 = Vijay | first1 = Venugopalan | last2 = Rao | first2 = Arun D. | last3 = Narayan | first3 = K. S. | date = 2011 | journal = J. Appl. Phys. | volume = 109 | issue = 8 | pages = 084525–084525–6 | doi = 10.1063/1.3580514 |bibcode = 2011JAP...109h4525V }}</ref><ref>{{cite journal | title = Electronic Properties of Transparent Conductive Films of PEDOT:PSS on Stretchable Substrates | last1 = Darren | last2 = Vosgueritchian | first2 = Michael | last3 = Tee | first3 = C.-K. | last4 = Bolander | first4 = John A. | last5 = Bao | first5 = Zhenan | date = 2012 | journal = Chem. Mater. | volume = 24 | issue = 2| pages = 373–382 | doi = 10.1021/cm203216m }}</ref> which are largely amorphous.

==Properties and applications==
Conductive polymers show promise in antistatic materials<ref name=Ullmann/> and they have been incorporated into commercial displays and batteries. Literature suggests they are also promising in [[organic solar cells]], [[Printed electronics|printed electronic circuits]], [[Organic LED|organic light-emitting diodes]], [[actuator]]s, [[electrochromism]], [[supercapacitors]], [[chemiresistor#Conductive polymers|chemical sensors]], [[chemical sensor array]]s, and [[biosensors]],<ref>{{cite journal | doi =  10.1016/j.aca.2008.02.068 | title =  Conducting polymers in chemical sensors and arrays | date =  2008 | last1 =  Lange | first1 =  Ulrich | last2 =  Roznyatovskaya | first2 =  Nataliya V. | last3 =  Mirsky | first3 =  Vladimir M. | journal =  Analytica Chimica Acta | volume =  614 | pages =  1–26 | pmid =  18405677 | issue =  1| bibcode = 2008AcAC..614....1L }}</ref> flexible transparent displays, [[electromagnetic shielding]] and possibly replacement for the popular transparent conductor [[indium tin oxide]]. Another use is for [[microwave]]-absorbent coatings, particularly radar-absorptive coatings on [[stealth aircraft]]. Conducting polymers are rapidly gaining attraction in new applications with increasingly processable materials with better electrical and physical properties and lower costs. The new nano-structured forms of conducting polymers particularly, augment this field with their higher surface area and better dispersability. Research reports showed that nanostructured conducting polymers in the form of nanofibers and [[nanosponges]] exhibit significantly improved capacitance values as compared to their non-nanostructured counterparts.<ref>{{cite journal|last1=Tebyetekerwa|first1=Mike|last2=Wang|first2=Xingping|last3=Wu|first3=Yongzhi|last4=Yang|first4=Shengyuan|last5=Zhu|first5=Meifang|last6=Ramakrishna|first6=Seeram|title=Controlled synergistic strategy to fabricate 3D-skeletal hetero-nanosponges with high performance for flexible energy storage applications|journal=Journal of Materials Chemistry A|date=2017|volume=5|issue=40|pages=21114–21121|doi=10.1039/C7TA06242G}}</ref><ref name="Unveiling Polyindole 2017">{{cite journal|last1=Tebyetekerwa|first1=Mike|last2=Yang|first2=Shengyuan|last3=Peng|first3=Shengjie|last4=Xu|first4=Zhen|last5=Shao|first5=Wenyu|last6=Pan|first6=Dan|last7=Ramakrishna|first7=Seeram|last8=Zhu|first8=Meifang|title=Unveiling Polyindole: Freestanding As-electrospun Polyindole Nanofibers and Polyindole/Carbon Nanotubes Composites as Enhanced Electrodes for Flexible All-solid-state Supercapacitors|journal=Electrochimica Acta|date=September 2017|volume=247|pages=400–409|doi=10.1016/j.electacta.2017.07.038}}</ref>

With the availability of stable and reproducible dispersions, PEDOT and [[polyaniline]] have gained some large-scale applications. While PEDOT ([[poly(3,4-ethylenedioxythiophene)]]) is mainly used in antistatic applications and as a transparent conductive layer in form of PEDOT:PSS dispersions (PSS=[[Sodium polystyrene sulfonate|polystyrene sulfonic acid]]), polyaniline is widely used for [[printed circuit board manufacturing]] – in the final finish, for protecting copper from corrosion and preventing its solderability.<ref name="nalwa">{{cite book |last=Wessling |first=Bernhard |title=Handbook of Nanostructured Materials and Nanotechnology |publisher=Academic Press |year=2000 |isbn=978-0-12-513760-7 |editor=in: Nalwa, H.S. |volume=5 |place=New York, USA |pages=501–575 |doi=10.1016/B978-012513760-7/50070-8 |s2cid=185393455}}</ref> Moreover, polyindole is also starting to gain attention for various applications due to its high redox activity,<ref>{{cite journal|last1=Tebyetekerwa|first1=Mike|last2=Xu|first2=Zhen|last3=Li|first3=Weili|last4=Wang|first4=Xingping|last5=Marriam|first5=Ifra|last6=Peng|first6=Shengjie|last7=Ramakrishna|first7=Seeram|last8=Yang|first8=Shengyuan|last9=Zhu|first9=Meifang|title=Surface Self-Assembly of Functional Electroactive Nanofibers on Textile Yarns as a Facile Approach Towards Super Flexible Energy Storage|journal=ACS Applied Energy Materials|volume=1|issue=2|pages=377–386|date=13 December 2017|doi=10.1021/acsaem.7b00057}}</ref> thermal stability,<ref name="Unveiling Polyindole 2017"/> and slow degradation properties than competitors polyaniline and polypyrrole.<ref>{{cite journal|last1=Zhou|first1=Weiqiang|last2=Xu|first2=Jingkun|title=Progress in Conjugated Polyindoles: Synthesis, Polymerization Mechanisms, Properties, and Applications|journal=Polymer Reviews|date=18 August 2016|volume=57|issue=2|pages=248–275|doi=10.1080/15583724.2016.1223130|s2cid=99946069}}</ref>

=== Electroluminescence ===
[[Electroluminescence]] is light emission stimulated by electric current. In organic compounds, electroluminescence has been known since the early 1950s, when Bernanose and coworkers first produced electroluminescence in crystalline thin films of acridine orange and quinacrine. In 1960, researchers at Dow Chemical developed AC-driven electroluminescent cells using doping. In some cases, similar [[light emission]] is observed when a [[voltage]] is applied to a thin layer of a conductive organic polymer film. While electroluminescence was originally mostly of academic interest, the increased conductivity of modern conductive polymers means enough power can be put through the device at low voltages to generate practical amounts of light. This property has led to the development of [[flat panel display]]s using [[organic LED]]s, [[Photovoltaic module|solar panel]]s, and optical [[amplifier]]s.

===Barriers to applications===
Since most conductive polymers require oxidative doping, the properties of the resulting state are crucial. Such materials are salt-like (polymer salt), which makes them less soluble in organic solvents and water and hence harder to process. Furthermore, the charged organic backbone is often unstable towards atmospheric moisture. Improving processability for many polymers requires the introduction of solubilizing substituents, which can further complicate the synthesis.

Experimental and theoretical thermodynamical evidence suggests that conductive polymers may even be completely and principally insoluble so that they can only be processed by [[Dispersion (chemistry)|dispersion]].<ref name="nalwa"/>

===Trends===
Most recent emphasis is on [[organic light emitting diode]]s and organic [[polymer solar cell]]s.<ref>[http://www.mrs.org/s_mrs/sec_subscribe.asp?CID=2235&DID=82525&action=detail Overview on Organic Electronics] {{Webarchive|url=https://web.archive.org/web/20170302184725/http://www.mrs.org/s_mrs/sec_subscribe.asp?CID=2235&DID=82525&action=detail |date=2017-03-02 }}. Mrs.org. Retrieved on 2017-02-16.</ref> The Organic Electronics Association is an international platform to promote applications of [[organic semiconductor]]s. Conductive polymer products with embedded and improved electromagnetic interference (EMI) and electrostatic discharge (ESD) protection have led to both prototypes and products. For example, Polymer Electronics Research Center at University of Auckland is developing a range of novel DNA sensor technologies based on conducting polymers, photoluminescent polymers and inorganic nanocrystals (quantum dots) for simple, rapid and sensitive gene detection. Typical conductive polymers must be "doped" to produce high conductivity. As of 2001, there remains to be discovered an organic polymer that is ''intrinsically'' electrically conducting.<ref>[http://alumnus.caltech.edu/~colinc/science/past/PhD/html-thesis/node8.html Conjugated Polymers: Electronic Conductors] {{Webarchive|url=https://web.archive.org/web/20150211153956/http://alumnus.caltech.edu/~colinc/science/past/PhD/html-thesis/node8.html |date=2015-02-11 }} (April 2001)</ref> Recently (as of 2020), researchers from [[IMDEA Nanoscience Institute]] reported experimental demonstration of the rational engineering of 1D polymers that are located near the [[quantum phase transition]] from the topologically trivial to non-trivial class, thus featuring a narrow bandgap.<ref>{{Cite journal|last1=Cirera|first1=Borja|last2=Sánchez-Grande|first2=Ana|last3=de la Torre|first3=Bruno|last4=Santos|first4=José|last5=Edalatmanesh|first5=Shayan|last6=Rodríguez-Sánchez|first6=Eider|last7=Lauwaet|first7=Koen|last8=Mallada|first8=Benjamin|last9=Zbořil|first9=Radek|last10=Miranda|first10=Rodolfo|last11=Gröning|first11=Oliver|date=2020-04-20|title=Tailoring topological order and π- conjugation to engineer quasi-metallic polymers|url=https://www.nature.com/articles/s41565-020-0668-7|journal=Nature Nanotechnology|language=en|pages=437–443|doi=10.1038/s41565-020-0668-7|issn=1748-3395|volume=15|issue=6|pmid=32313219|arxiv=1911.05514| bibcode=2020NatNa..15..437C |s2cid=207930507}}</ref>

==See also==
{{Portal|Chemistry|Physics}}
* [[Organic electronics]]
* [[Organic semiconductor]]
* [[Molecular electronics]]
* [[List of emerging technologies]]
* [[Conjugated microporous polymer]]

==References==
{{Reflist|30em}}

==Further reading==
* {{cite journal | doi = 10.1126/science.291.5502.263 | title = MOLECULAR METALS: Staying Neutral for a Change | date = 2001 | last1 = Cassoux | first1 = P. | journal = Science | volume = 291 | issue = 5502 | pages = 263–4 | pmid = 11253216| s2cid = 93139551 }}
* {{cite journal | doi =10.1196/annals.1292.016 | title =An Overview of the First Half-Century of Molecular Electronics | date =2003 | last1 =Hush | first1 =Noel S. | journal =Annals of the New York Academy of Sciences | volume =1006 | issue =1 | pages =1–20 | pmid=14976006|bibcode = 2003NYASA1006....1H | s2cid =24968273 }}
* {{cite journal|pmid=15535637|pages=4891–4945|url=http://perepichka-group.mcgill.ca/papers/28.pdf|date=2004|last1=Bendikov|first1=M|last2=Wudl|first2=F|last3=Perepichka|first3=DF|author-link3=Dmitrii Perepichka|title=Tetrathiafulvalenes, oligoacenenes, and their buckminsterfullerene derivatives: The brick and mortar of organic electronics|volume=104|issue=11|doi=10.1021/cr030666m|journal=Chemical Reviews|access-date=2012-05-19|archive-url=https://web.archive.org/web/20130717222050/http://perepichka-group.mcgill.ca/papers/28.pdf|archive-date=2013-07-17|url-status=dead}}
* Hyungsub Choi and Cyrus C.M. Mody [http://sss.sagepub.com/cgi/content/abstract/39/1/11 The Long History of Molecular Electronics] Social Studies of Science, vol 39.
* {{cite journal | doi =10.1016/0022-0248(76)90115-9 | title =Filamentous growth of carbon through benzene decomposition | date =1976 | last1 =Oberlin | first1 =A. | last2 =Endo | first2 =M. | last3 =Koyama | first3 =T. | journal =Journal of Crystal Growth | volume =32 | issue =3 | pages =335–349|bibcode = 1976JCrGr..32..335O }}
* F. L. Carter, R. E. Siatkowski and H. Wohltjen (eds.), ''Molecular Electronic Devices'', 229–244, North Holland, Amsterdam, 1988.

==External links==
* [http://www.rsc.org/Publishing/Journals/CS/Article.asp?Type=Issue&JournalCode=CS&Issue=7&Volume=39&SubYear=2010 Conducting Polymers for Carbon Electronics] – a [http://www.rsc.org/Publishing/Journals/CS/Index.asp ''Chem Soc Rev''] themed issue with a foreword from [[Alan Heeger]]

{{emerging technologies|topics=yes|robotics=yes|manufacture=yes|materials=yes}}

{{Authority control}}

{{DEFAULTSORT:Conductive Polymer}}
[[Category:Conductive polymers| ]]
[[Category:Molecular electronics]]
[[Category:Organic semiconductors]]
[[Category:Polymer material properties]]