Processible conjugated polymers: from organic semiconductors to organic metals and superconductors
Introduction
Polymers with spatially extended π-bonding system, here abbreviated as ‘conjugated polymers’, although known for many years, did not draw significant research attention till the mid 1970s. This was caused by the fact that in their vast majority they were intractable and, in many respects, showed inferior properties as compared to already developed polymers. Before 1977, papers dealing with polyconjugated systems were rare and the research devoted to these materials was not systematic. Neither molecular nor electronic structures of conjugated polymers in their undoped state were elucidated. Moreover, the chemical nature of the doping reactions which render these polymers conductive was not known similarly as the mechanism of their conductivity, despite the fact that few papers describing unusually high conductivity of some conjugated polymers were published. In 1977 Heeger, MacDiarmid and Shirakawa showed that poly(acetylene), which is the simplest polyconjugated system, can be rendered conductive by the reaction with bromine or iodine vapors [1]. Spectroscopic studies that followed demonstrated without any ambiguity that this reaction is redox in nature and consists of the transformation of neutral polymer chains into polycarbocations with simultaneous insertion of the corresponding number of Br3− or I3− anions between the polymer chains in order to neutralize the positive charge imposed on the polymer chain in course of the doping reaction [2]. This important discovery initiated an extensive and systematic research devoted to various aspects of the chemistry and physics of conjugated polymers both in their neutral (undoped) and charged (doped) states. According to SCIFINDER almost 40,000 scientific papers were published in this field of research since 1977. This previously underestimated family of macromolecular compounds turned out to be extremely interesting both from the basic research and application points of view. As a result, in 2000, Heeger, MacDiarmid and Shirakawa — the founders of the ‘conjugated polymer science’ — were granted Nobel Prize in chemistry [3], [4], [5]. Another exciting event followed shortly after the attribution of the Noble Prize for conducting polymers. Schön et al. [6] demonstrated that regioregular poly(3-hexylthiophene) if used in a field-effect transistor (FET) configuration becomes superconducting at 2.35 K. This is the first case of superconductivity in an organic polymer, albeit not the first example of a superconducting polymer since superconductivity in an inorganic polymer-poly(sulfur nitride): (SN)x– was discovered more than two decades ago [7].
In the past four years few review papers on various aspects of conjugated and conductive polymers were published in ‘Progress in Polymer Science’ [8], [9], [10], [11], [12], [13]. For this reason, in our paper we will concentrate on problems, which either were not discussed in previous contributions or, despite their importance, mentioned only briefly. Special emphasis will be put on the development in the conjugated polymer field observed in the last two years. The organization of this paper is as follows. In Section 2 we describe the synthesis of conjugated polymers in their undoped (semiconducting state), their basic chemical and physical properties and their applications, as semiconductors, in molecular electronics devices. In Section 3, we discuss the doping process which transforms ‘polymeric semiconductors’ into ‘polymeric metals’ with special emphasis on processes improving the processibility of these materials. Similarly as in Section 2 we describe basic chemical and physical properties of these polymeric metals and their application. In Section 4 we discuss electric field-induced superconductivity in poly(acene)s and poly(thiophene)s. In general, with the exception of poly(acene)s, in our paper we focus on truly polymeric systems. It should be however noted that equally intensive research is presently carried out for conjugated oligomers.
The selection of papers quoted is purely subjective and reflects our research interests. We are aware of the fact that the number of papers cited (321) constitute significantly less than 1% of all papers devoted to electroactive polyconjugated systems. Several important contributions had to be omitted due to space limits.
Section snippets
Basic characteristics
It is convenient to start the discussion of the peculiarities of macromolecular polyconjugated systems by the description of the electronic structure of poly(acetylene) for two reasons. First, poly(acetylene) is the simplest conjugated polymer and for this reason can be considered as a prototype of other polyconjugated systems. Second, historically the discovery of poly(acetylene) doping triggered the explosion of the research devoted to electroactive polymers.
Poly(acetylene) (–CHCH–)x can
Principles of conjugated polymers doping
Before describing structural and electronic properties of doped conjugated polymers, it is instructive to discuss the chemical nature of the doping process. Two types of dopings are usually distinguished — the redox-type doping and the acid–base one.
Poly(acetylene), poly(p-phenylene), polyheterocyclic polymers (poly(thiophene), poly(pyrrole), poly(furan) and their derivatives) and other polyconjugated systems with no strong basic centers in their backbone usually undergo the redox-type doping.
Polymeric superconductors
Before discussing the superconductivity of conjugated polymers, it is instructive to describe briefly the historical development of the studies on the superconductivity of low molecular weight organic conductors. The first organic superconductor was discovered in the early 1980s [314]. It was prepared by electrochemical oxidation of tetramethyl tetraselena fulvalene (TMTSeF) to give an ion radical salt of the following stoichiometry (TMTSeF)2+·X− (where X− is a monovalent anion of ClO4−, PF6−
References (321)
- et al.
Raman scattering in (CH)x and (CH)x treated with bromine and iodine
Solid State Commun
(1979) Intrinsically electrically conducting polymers. Synthesis, characterization and their applications
Progr Polym Sci
(1998)- et al.
Polyaniline: a polymer with many interesting redox states
Progr Polym Sci
(1998) - et al.
Conducting polyaniline blends and composites
Progr Polym Sci
(1998) - et al.
Synthesis and application of thiophene-based functional polymers
Progr Polym Sci
(1998) - et al.
Conducting polymers prepared by oxidative polymerization: polyaniline
Progr Polym Sci
(1998) - et al.
Blue light emitting polymers
Progr Polym Sci
(2000) Aniline in history and technology
Endeavour New Ser
(1993)- et al.
A new synthesis of poly(acetylene)
Polym Commun
(1980) - et al.
Spectroelectrochemical study of polypyrrole films
J Electroanal Chem
(1983)
Processible and environmentally stable conducting polymers
Synth Met
Thermochromic and solvatochromic effects in poly(3-hexylthiophene)
Synth Met
Electrochemical preparation of conducting polyalkythiophene films
Synth Met
Electrochemical synthesis and spectroscopic study of poly(3-alkylthienylenes)
Synth Met
Chemical synthesis and characterization of soluble poly(4,4′-dialkyl-2,2′-bithiophenes)
Polymer
A general synthetic route to high molecular weight poly(p-xylylene) derivatives: a new route to poly(p-phenylene vinylene)
Synth Met
The effect of oxidation conditions on the chemical polymerization of polyaniline
Synth Met
Synthesis of high molecular weight polyaniline at low temperatures
Synth Met
Low temperature synthesis of high molecular weight polyaniline
Polymer
Controlled polymerization of aniline at sub-zero temperatures
Synth Met
Emulsion polymerization of aniline
Synth Met
Emulsion polymerization of aniline
Polymer
Homogeneous route to polyaniline
Synth Met
Oxidative degradation pathway of polyaniline film electrodes
J Electroanal Chem
Spectroelectrochemical studies of polyaniline
Synth Met
The effect of anions of supporting electrolyte on the electrochemical polymerization of aniline and the properties of polyaniline
Synth Met
Cyclic potential sweep electropolymerization of aniline. The role of anions in the polymerization mechanism
J Electroanal Chem
Spectroelectrochemical evidence for an intermediate in the electropolymerization of aniline
J Electroanal Chem
Redox mechanism and electrochemical behaviour of polyaniline deposits
J Electroanal Chem
Effect of electropolymerization temperature on structural, morphological and conductive properties of poly(aniline) deposits prepared in 1,2-dichloroethane without a proton donor
J Electroanal Chem
Synthesis of electrically conducting organic polymers: halogen derivatives of poly(acetylene), (CH)x
J Chem Soc, Chem Commun
The discovery of polyacetylene film: the dawning of an era of conducting polymers (Nobel lecture)
Angew Chem Int Ed
Synthetic metals: a novel role for organic polymers (Nobel lecture)
Angew Chem Int Ed
Semiconducting and metallic polymers: the fourth generation of polymeric materials (Nobel lecture)
Angew Chem Int Ed
Gate-induced superconductivity in a solution-processed organic polymer film
Nature
Superconductivity in polysulfur nitride (SN)x
Phys Rev Lett
Polyacetylene: new concepts and new phenomena
Poly(isothianaphtene)
J Org Chem
Synthetic principles for bandgap control in linear π-conjugated systems
Chem Rev
Low band gap conducting polymers
Conjugated aromatic polyazomethines. 1. Characterization of structure, electronic spectra and processing of thin films from soluble complexes
Chem Mater
Conjugated aromatic polyimines. 2. Synthesis, structure and properties of new aromatic polyazomethines
Macromolecules
Synthesis of polyacetylene
Polycyclooctatetraene (polyacetylene): synthesis and properties
J Am Chem Soc
Polyacetylene-chemistry, physics and material science
Electrochemical studies of some conducting polythiophene films
J Phys Chem
A new method for preparation of electrically conductive polythiophenes
J Polym Sci, Part C: Polym Lett
Electrochemical polymerization of thiophenes in the presence of bithiophene or terthiophene: kinetics and mechanism of the polymerization
Chem Mater
Highly conducting, soluble, and environmentally-stable poly(3-alkylthiophenes)
J Chem Soc, Chem Commun
Chromism of soluble polythienylenes
J Polym Sci, Part B: Polym Phys
Cited by (678)
Synthesis and investigation of polymers containing aniline and indole fragments
2023, Materials Today CommunicationsSolution processable polypyrrole nanotubes as an alternative hole transporting material in perovskite solar cells
2023, Materials Today CommunicationsVisible-light responsive Au nanoparticle-decorated polypyrrole-carbon black/SnO<inf>2</inf> ternary nanocomposite for ultrafast removal of insecticide imidacloprid and methylene blue
2023, Journal of Industrial and Engineering ChemistryConducting polymers as gas sensing material
2023, Carbon Nanomaterials and their Nanocomposite-Based Chemiresistive Gas Sensors: Applications, Fabrication and CommercializationPolymer/fullerene nanomaterials in optoelectronic devices: Photovoltaics, light-emitting diodes, and optical sensors
2023, Polymer/Fullerene Nanocomposites: Design and Applications