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      Investigation of charge carriers in doped thiophene oligomers through theoretical modeling of their UV/Vis spectra

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      Author
      Salzner, U.
      Date
      2008
      Source Title
      Journal of Physical Chemistry A
      Print ISSN
      1089-5639
      Volume
      112
      Issue
      24
      Pages
      5458 - 5466
      Language
      English
      Type
      Article
      Item Usage Stats
      104
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      Abstract
      The nature of the charge carriers in conducting organic polymers (COPs) is a long standing problem. Polythiophene is one of the prototypes of COPs and intensively studied. Because doping leads to changes in UV/vis spectra that are characteristic of the absorbing species, UV/vis spectra of charged thiophene oligomers with up to 25 rings were calculated with time-dependent density functional theory. The credibility of the method was established by comparing the results with a variety of theoretical levels and with experiment. Effects due to counterions (Cl3-) and solvent (CH 2Cl2) were examined. It was found that TDDFT employing hybrid functionals is accurate enough to distinguish the absorbing species. The findings offer an explanation for the experimentally observed difference in UV-spectra of medium-sized and long oligomers upon doping. As chain lengths of the oligomers increase and energy levels get closer, configuration interaction leads to additional absorption peaks in the high energy sub-band region (at around 1.5-2.5 eV). Thus, long oligomers do not behave differently from medium-sized ones upon doping, only their spectra are different. At low doping levels radical cations (polarons) are produced. At higher doping levels, dications that harbor weakly interacting polaron pairs are formed. Bipolarons are predicted only on very short chains or at high doping levels. There is no bipolaron binding energy and disproportionation of monocations into dications and neutral species is energetically unfavorable. © 2008 American Chemical Society.
      Keywords
      ABS resins
      Civil aviation
      Conducting polymers
      Density functional theory
      Oligomers
      Organic polymers
      Polymers
      Probability density function
      Sulfur compounds
      Thiophene
      Conducting organic polymers
      Counter-ions
      Long standing
      Poly-thiophene
      Thiophene oligomers
      Time-dependent density functional theory
      UV/Vis spectra
      Charge carriers
      Permalink
      http://hdl.handle.net/11693/23083
      Published Version (Please cite this version)
      http://dx.doi.org/10.1021/jp800606m
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