P Py and Poly thiophenes

These results established early on that the charge carriers responsible for conduction in CPs may not be electrons and may be spinless bipolarons, and gave an impetus to explanations of CP behavior based on condensed matter physics. Scott et al. [450] postulated that the ESR signal in doped P(Py) arises from accidental, neutral tt-radical defects which are more prominent in the oxidized state of the CP. A similar explanation, i.e. that impurities (including metals and oxygen) in the oxidized state of the CP may be responsible for the ESR signal in most CPs where bipolarons (as opposed to polarons and solitons) are the presumed majority charge carriers, is now widely accepted. 

The ESR spectra of P(Ac) have also been studied in some detail. As-prepared, pure cis-P(Ac) shows no detectable ESR signal [453]. Trans-P(Ac), which is generally obtained via thermal, chemical or electrochemical conversion from the cis-form shows an ESR signal which is the result of these conversions introducing fixed and mobile defects (such as solitons) or impurities [454]. Indeed, cis-trans isomerization in P(Ac) can be conveniently followed by ESR (cf. Fig. 11-411. 

11-41 Evolution of the ESR signal for various levels of doping in chemically (a) and electrochemically (b) doped (CHyNa), [5.82] and (CHyLi [5.210], respectively. Ilie arrow shows the increasing field direction. At high doping levels, the lineshape is Dysonian in contrast to the Gaussian lineshape for the pure cis material. After Reference [440], reproduced with permission. 

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