Doping with iodine

Third, metallocene units, such as ferrocene or ruthenocene, have been linked to phosphazene cyclic trimers or tetramers and these were polymerized and substituted to give polymers of the type mentioned previously (41). Polyphosphazenes with ferrocenyl groups can be doped with iodine to form weak semiconductors. Polymer chains that bear both ruthenocenyl and ferrocenyl side groups are prospective electrode mediator systems. 

The silver(I) complexes with the tetrakis(methylthio)tetrathiafulvalene ligand have been reported, the nitrate salt presents a 3D structure with an unprecedented 4.16-net porous inorganic layer of silver nitrate,1160 the triflate salt presents a two interwoven polymeric chain structure.1161 The latter behaves as a semiconductor when doped with iodine. With a similar ligand, 2,5-bis-(5,5,-bis(methylthio)-l,3,-dithiol-2 -ylidene)-l,3,4,6-tetrathiapentalene, a 3D supramolecular network is constructed via coordination bonds and S"-S contacts. The iodine-doped compound is highly conductive.1162 (Methylthio)methyl-substituted calix[4]arenes have been used as silver-selective chemically modified field effect transistors and as potential extractants for Ag1.1163,1164... 

The synthesis and properties of heat-resistant polyazomethines containing 2,5-disubstituted oxadiazole fragments, being insulators convertible into semiconductors by doping with iodine, have been described. The radical copolymerization of alkenes with the fluorescent co-monomer 2-/-butyl-5-(4 -vinyl-4-biphenylyl)-l,3,4-oxadiazole has resulted in useful macromolecular scintillators. Anionic polymerization of 2-phenyl-l,3,4-oxadiazolin-5-one has produced a nylon-type product <1996CHEC-II(4)268>. 

Electrically insulating films of polyacetylene, doped with iodine and sodium, became semiconductive (Shirakawa, MacDiarmid, Heeger, 1976). 

Semiconducting black polymers characterized as 44 have been prepared via slow heating of triple-decker (allyl)nickel diborolyl triple-decker complexes.44 EXAFS studies reveal an Ni-Ni distance of 3.35 A and a powder conductivity of ca. 10-2 S cm-1. When doped with iodine or oxygen, the conductivity of these polymers... 

Note 2 The electric conductivity of a conjugated polymer is markedly increased by doping it with an electron donor or acceptor, as in the case of polyacetylene doped with iodine. 

The tetrabutylammonium salts of the bis chelates are semiconductors but exhibit enhanced conducting properties after doping with iodine. The corresponding salts which are formed when Bi N is replaced by TTF+ or TSeF+ have higher conductivities than the analogous dithiolene complexes with magnitudes similar to that of TTF-TCNQ (TTF = tetrathiafulvalene, TSeF = tetraselenofulvalene, TCNQ = tetracyano-p-quinodimethane). 

Several attempts to induce orientation by mechanical treatment have been reviewed 6). Trans-polyacetylene is not easily drawn but the m-rich material can be drawn to a draw ratio of above 3, with an increase in density to about 70% of the close-packed value. More recently Lugli et al. 377) reported a version of Shirakawa polyacetylene which can be drawn to a draw ratio of up to 8. The initial polymer is a m-rich material produced on a Ti-based catalyst of undisclosed composition and having an initial density of 0.9 g cm-3. On stretching, the density rises to 1.1 g cm-3 and optical and ir measurements show very high levels of dichroism. The (110) X-ray diffraction peak showed an azimuthal width of 11°. The unoriented material yields at 50 MPa while the oriented film breaks at a stress of 150 MPa. The oriented material, when iodine-doped, was 10 times as conductive (2000 S cm-1) as the unstretched film. By drawing polyacetylene as polymerized from solution in silicone oil, Basescu et al.15,16) were able to induce very high levels of orientation and a room temperature conductivity, after doping with iodine, of up to 1.5 x 10s S cm-1. 

In contrast, the electrical conductivity tends to become higher with a lower silole content, reaching up to 2.4 S cm-1 upon doping with iodine. The bulky (t-butyldimethylsiloxy)methyl side groups in the silole unit are oriented out of the n-conjugated polymer plane and hence hinder the interaction between the polymer chains, which is known to be one of the key factors for high conductivity values174. 

These quarternized polymers can be viewed as self-doped but exhibit relatively low intrinsic conductivities. The polymers can be oxidatively doped with iodine, or reductively doped with TTF, to give highly conducting polyacetylenes with conductivities of 10"4 and 10 1 S/cm, respectively. One additional attractive feature of this system is that, unlike PA, these quarternized PAs are very stable in air. 

Table 5.3 Conductivities of Polysilanes (S cm-1) Doped with Iodine or FeCl3a...

Dithienosilole-thiophene alternating copolymer 21 is the important example for the electrical conduction of SCPs.42 When the copolymer is doped with iodine, a high electrical conductivity of 400 S cm-1 can be achieved. This value is the highest among SCPs and is also close to that of well-defined poly(3-alkylthiophene). 

Doping with iodine, on the other hand, gave lower conductivities (ca 10-6 to 10-8 Scm-1, see Table 1), but which could be correlated with the ionization potentials of the polymers (lower ionization potentials giving higher conductivity). This is consistent with simple electron transfer from the polysilane to the iodine, with formation of delocalized holes along the polysilane chain. 

TABLE 1. Conductivities of polysilanes (Scm ) doped with iodine or Fecl3 ... 

Upon doping with iodine vapor. Determined on thin films of polymers cast on glass substrate by the use of the four-probe technique. 

The first conductive LB film, consisting of C PyfTCNQ) doped with iodine (Fig. 3) belongs to the class of anion-radical salts [20]. The insulating C PyCTCNQ) LB film was rendered conductive by iodine doping, and the bulk conductivity was about 0.01 S/cm. The nominal charge of TCNQ of... 

Figure 4 Structure of C22Py(TCNQ) LB film doped with iodine. (From Ref. 33.)...

The LB films of TTF [73,74] and BEDT-TTF [75-81] derivatives were investigated and secondary treatments, such as iodine or ICI doping, rendered the films conductive. The structure of the LB film of C18TET-TTF doped with iodine is investigated by UV/visible and IR spectroscopies [76— 79]. The initial stage of the chemical reaction involves formation of the cation radical of the donor, which is converted spontaneously into a dimeric form. At this step the film is insulating. Gradual evaporation of I2 from the film takes place afterward and the conductivity of the film reaches a maximum of about 0.1 S/cm. (See the footnote in Section II.A. 1.)... 

Fig. 9.35 Temperature dependence of the conductivity of doped PAcs. (a) A and B, doped with CIO4 C, doped with FeCl3 the other curves are for M0CI5 doping and (b) doped with iodine. Reproduced with permission of Wiley-VCH from Kaiser (2001b).

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