Other CPs

Although the ESR of many other CPs in the undoped as well as doped states has been studied [458], many of these, for instance P(PPV) [449] and P(PPS) [467], display anomalous behavior not open to clear interpretation in terms of the expected charge carriers and doping/conductivity behavior in these CPs. There are also limitations to the interpretation of ESR data. For example, Wang et al., in their study of the emeraldine base for of P(o-toluidine), find a g factor of ca. 2.0054, close to that for an electron proximate to a N-H bond, which they take to indicate that the unpaired electron is delocalized over about one monomer unit only, a contention not entirely borne out by other experimental data [191]. 

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Other CP MAS studies of bacteriorhodopsin, proteorhodopsin as well as bathorhodopsin have been reported.75-7... 

E, Essential oil F, Fatty oil P, Pungent constituent C, Colour A, Antioxidant O, Other CP, Commercial production. 

In the late 1970s Heeger and MacDiarmid found that polyacetylene [(CH)n] produced by Shirikawa s method exhibited a 12 order of magnitude increase in electrical conductivity when exposed to oxidizing agents. Since that discovery, a vast array of other CPs have been synthesized. The most common of these, in addition to polyacetylene, are shown below in Scheme 1. 

In contrast to polyacetylene, the other CPs shown in Scheme 1 have non-degenerate ground states (i.e. they do not possess two equivalent resonance forms), and thus, do not show evidence of soliton formation. In this instance, the oxidation of the CP is believed to result in the destabilization (raising of the energy) of the orbital from which the electron is removed. This orbital s energy is... 

Thus, quantum-chemical analysis confirms the mechanism of O2 electroreduction and gives possibility to understand the reasons of catalytic activity of such class new catalysts as PANI and some other CPs. 

In a first approximation supra-Cp metal complexes can be prepared the same way as normal or other Cp-metal and organo-metal bonds in general. The methods used most often (see Appendix) are the metathesis reaction [Eq. (1)] followed in number by oxidative additions (Eq. (2)] and metallation/deprotonation reactions [Eq. (3)]. The latter is especially important for the cyclpentadienyl alkali metal compounds. A useful variation of reaction (3) is the formation of CpTl in an acid/base reaction from cyclopentadiene and thallium ethoxide [Eq. (3b)]. This represents a convenient route to cyclopentadienylthallium compounds, which are also valued (in place of Cp alkalis) as mild Cp-transfer reagents for the synthesis of difficultly isolable cyclopentadienyl derivatives (77). 

The only other Cp structure of potassium known is the one of the base-free (Me3Si)H4C5K (139) which consists of parallel, one-dimensional zig-zag strands (as in 14). Analogous to many CpTl and Cpln structures (see above) the potassium sits equidistantly between two Cp rings with an electrostatic interaction between the counterions. The tetrahydrofuran coordination surely plays a role in the monomerization of the structure of the title compound (although it is not clear to what extent). The K-Cp distances in both complexes, however, are essentially identical. The preparation and crystal structure of MejCsK(pyridine)2, which has a linear zig-zag chain structure, has been described recently (179b). 

Many other CPs have been prepared during the past decade or so some of them are shown on Table 1, but most properties discussed in Chapters 11 to 13 can be presented using PA, PTh, and PAni, and a few of their derivatives, with, in addition, polyphenylenevinylene (PPV) when electroluminescence is discussed. 

The discussion above left aside an entire class of CPs, the polydiacetylenes (PDAs) (see Table 1). Their study has followed a path similar to that of other CPs, but with only occasional intersections. Indeed, they differ greatly from other CPs in many respects. PDAs have a feature that is almost unique in the entire polymer field, and not only among CPs single crystals of macroscopic size can be obtained. They owe that to their peculiar polymerization mechanism, which is a topotactic reaction occurring in the mon-... 

Another feature that sets the PDAs aside from other CPs is that most attempts at doping them have been unsuccessful. In the days where obtaining the highest (reversible) conductivity was a major goal, that was a severe drawback. On the other hand, PDAs have large third-order nonlinear optical susceptibilities, even compared to other CPs (in fact, this property of undoped CPs was discovered on a PDA in 1976 [55]), and this is presently an active field of study [56]. 

Polyaniline differs from other CPs in that the doping process may be associated with protonation of the N atoms in the chain (i.e., to a base <- salt equilibrium in the presence of acid, in addition to the usual redox reactions). This is discussed further in Chapter 13. The related processes are therefore more complex. On the other hand, the low cost and proces-sibility of PAni makes it a prime candidate for several applications. 

In the undoped state, PAni is a base. Three molecular structures are possible, one of them being the so-called emeraldine base (EB) shown in Fig. 1 of Chapter 11 [52]. There are several differences between it and the other CP chains discussed above Due to the presence of the N atoms, the chain has a zigzag shape and the benzene rings have either a benzene-like or a quinone-like bond pattern (see Chapter 11, Section IV.B.l) and may be twisted. In principle, the number of independent structural parameters is even larger than for the other CPs. However, quite a good (albeit partial) understanding of the structure has been achieved, as shown in Ref. 24, for instance. 

EB is obtained as a totally amorphous solid (EB I) or a partially crystalline one (EB II), depending on the preparation or processing conditions [24] the crystallinity of EB II is about 50%. But stretching a film containing a plasticizer can increase its crystallinity (see Section II.D.2) [59]. The coherence lengths and dimensions of the two-dimensional projection of the structure are very similar to those of the other CPs (see Table 1), but... 

Figure 14 shows the unpolarized absorption spectra of films of polythiophene [124] and its hexamer a-sexithienyl [125]. The hexamer solution spectrum is at almost the same energy. As in Fig. 12a, the oligomer shows structure on its rising edge, and the polymer spectrum is structureless. But in Fig. 14 the absorption thresholds differ by = 0.2 eV only one would then say that conjugation extends in PT over only about six monomers. One could show similar data for many other CPs. 

The situation in other CPs seems to be more confused. PI A spectra often depend on temperature and time delay after pulse excitation. In trans-PA, at low enough temperature and a sufficiently long time, the PI A spectrum consists of three features a low-energy (LE) asymmetric ab-... 

In PPV a PI A peak at 1.4 eV has been assigned to a triplet-triplet transition from the triplet exciton [148,150], as in PDA (it is not known if the near equality in the energies is accidental). But, in addition, two other induced absorptions are observed near 0.6 and 1.6 eV, and since they are associated with the characteristic IR bands (such as the 0.45-eV band in PA), they should be due to a charged state. The absence of ODMR signal suggests that they have no spin and would then be bipolarons. In improved PPV (see Fig. 15), the PIA spectrum contains only the triplet peak [151], suggesting that the presence of the other features is a consequence of strong localization in a defective polymer. Similar results are found in other CPs, but up to now evidence for PIA due to polarons is elusive. 

The final picture of PDAs excitations is distinctly molecular. How much of it is applicable to other CPs ... 

The cause or causes of the opening of a gap in the band structure of trans-PA has been the subject of many theoretical papers and of much debate (see Chapter 11, Section IV.A and reviews and discussions in [17,146,147,181]). It would seem that electron-phonon and electron-election interactions are of comparable importance. If electron correlations are treated by adding a Hubbard on-site interaction term to the SSH Hamiltonian, the available experimental results for tram-PA are best accounted for by taking about equal values for the electron-phonon coupling X and for the Hubbard U. It might be that in other CPs the importance of electron correlations is greater. Note, however, that a U term (on-site interactions) is not enough to treat the correlations correctly, especially if excitons are to be studied (see the discussion of the PDA case above). 

Because of the role played by trans-PA as a prototype CP, other CPs have been discussed in the same terms as band-to-band transitions without excitons. The spectroscopic data reported above cast doubt on that approach, although recent results are still being so discussed [107] no consensus has yet been reached. 

Reaction of Cp W(CO)3Me with PF5 gives dinuclear (Cp WCl4)2 (structure unknown) from which a great variety of other Cp W compounds, such as Cp W(CH3)4 can be obtained.138... 

Before CP/M, there was no real operating system for these early computers, so it was quickly seized upon by most users and manufacturers of Z80 computers. There were no successfully competitive operating systems, and CP/M easily became a standard. Since almost everyone had CP/M, all the Z80 machines had more in common with each other. CP/M... 

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