Conjugated polymers chromicity

Although conjugated polymers can be both n-doped and p-doped - and thus, in principle, be capable of behaving either as negative or as positive electrodes - the majority of applications have been confined to the p-doping, positive side. Conductive polymers have been proposed and tested in a variety of advanced electrochemical devices. Due to lack of space, we will confine our attention to the description of the most illustrative examples which are rechargeable lithium batteries and multi-chromic optical displays. 

Even if the torsion of the chain of polythiophene could account for the chromic phenomena, we must still find good theoretical reasons why such a torsion should be possible. An ab initio theoretical study of the barriers to torsional flexibility in conjugated polymers in the gas phase [27], demonstrated that they are of the order of 0.7 ey clearly allowing conformational flexibility. This rationalizes the solubility of the polymers, but also warns that the polymer solid, where chain-chain interactions must be taken into account, is a rather different system. 

Another mechanism to realize electrochromism is electrothermal chromatic transition. Electricity is much easier to control compared to heat and most of the conductive materials, including many metals and conjugated polymers, can generate heat upon pass of electric current. Electrochromic device based on the electrothermal mechanism is generally composed of chromic and electrically conducting layers. 

Some conjugated polymers and liquid crystalline polymers which possess thermo-chromic properties are promising electrochromic materials. In comparison with the... 

Chromicity is widespread in conjugated polymers and an important topic. Prominent exan les of chromic conjugated polymers are the polytfaiophenes, the polybithiazoles, and the polydiacetylenes (1-3) (1-3). 

The utilization of such field-induced chromic effects 1 be the subject of this chapter and we will review some examples in which the external stimuli can be varied from heat, light, ions or biological moieties while the side-chain moieties are tuned accordingly. A brief presentation of conjugated polymers will be also provided as well as a presentation of different chromic polymers and finally some possible applications will be discussed. 

In spite of the large number of recent papers and reviews describing the synthesis, spectroelectrochemical properties and applications of electro-chromic materials or fluorescent conjugated polymers, there are just a few reports in the literature that describe the preparation, characterisation and... 

Chromic effects in conjugated polymers are not exclusive to polythiophenes but were indeed first observed in polydiacetylenes [43]. As reported for polythio-... 

The coupling of the electronic structure of the conjugated polythiophene to the conformation can account for chromic phenomena as well as for aspects of electronic transport of the materials in their undoped or doped states. The order-disorder transition of the polymer chains, between a planar and a non-planar state, is governed by molecular mechanisms related to the nature and regularity of side-chain substituents. 

The backbone of polymer 15 contains an alternating sequence of annulated five- and six-member rings. It is therefore reasonable to assume that all phenylene rings are more or less coplanar. As a consequence, the tt conjugation between the aromatic rings is even better than in polymer 11. This is reflected by a further batho-chromic shift of the longest wavelength absorption from Amax = 385 nm for II to Amax = 441 nm for 15 [61]. The... 

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