Tt-conjugated chain

Two basic approaches have been taken. The first consists in grafting organometallic donor and acceptor groups, such as ferrocene [as in [84] (Calabrese et al, 1991)] ruthenium derivatives [as in [83] (Whittall et al, 1996)] and tungsten carbonyl, instead of their organic counterparts on tt-conjugated chains. Quite successful in this respect, although not truly org nometallic, are zwitterions based on borate donors and ammonium acceptors [86] (Lambert et ah, 1996) and Lewis acid complexation as in [85] (Kammler et al, 1996). 

At present there are discrepancies between the description of internal rotation around bonds in the torsional functions used by various groups. Particularly in the case of TT-conjugated chains, important contributions to the variation in torsional energy arise from the differing interactions between the a and n components of... 

Fig. 7. Electronic effects upon increasing the number of repeat units in a coi jugated chain. In a very long chain, discrete energy levels are replaced by valence and conduction bands, and as the conjugation length is increased, the band gap is typically reduced, (a) TT-conjugated chain with few repeat units, (b) jr-conjugated chain with increased number of repeat units, and (c) r-conjugated polymer chain.

Functional siloles have found applications in the elaboration of silole-containing tt-conjugated systems. Because of its unique electronic properties, the introduction of a silole component or a silole cooligomer into an unsaturated chain should be a promising route to novel --electronic materials and, in this connection, the preparation of new heterocyclopentadiene monomeric precursors remains a current challenge. 

For both PF2/6 and PF8 the aforementioned main chain characteristics are essentially identical and so any pronounced differences are likely to originate in secondary structural characteristics of the functionalizing side chains. PF8 studies by Bradley and coworkers [16] first identified the unusual spectroscopic emission band now conventionally referred to as the phase . The hallmark signature of this peculiar chain structure is a relatively sharp series of emission bands red shifted some lOOmeV from those seen when the polymer is prepared in a glassy state, tt-Conjugated polymers have strong electron-phonon coupling and so, in addition to the it-it emission, there is a manifold of vibronic overtones spaced approximately 180 meV apart and red-shifted from the dominant n-n emission band. 

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