ESR and optical spectroscopy evidence for a chain-length dependence of the charged states of thiophene oligomers. Extrapolation to polythiophene

摘要: Abstract Correlated electron spin resonance (ESR) and optical absorption spectroscopy measurements have been carried out on soluble thiophene oligomers ( n T, standing for the number of rings) ring size = 6 12. Chemical oxidation leads to formation singly doubly charged molecules. On 6T, paramagnetic radical-cation 6T .+ diamagnetic dication ++ are successively generated, whereas (bipolaron) 12T twice longer molecule is directly produced. Both radical cation show two bands, which we used estimate bandgap corresponding species. This latter shown be a pertinent parameter studying chain-length dependence electronic properties oligomers. From comparison our results with previously published data polymers, find that short ⩽ 8) better described in terms molecular orbitals, one-electron model conjugated polymers more appropriate chains 12 polymer). The transition between long oligomers, occurs at 10±1 rings, corresponds chain enough bear independent polarons.