Effect of wave-function delocalization on the exciton splitting in organic conjugated materials

M. Muccini, M. Schneider, C. Taliani, M. Sokolowski, E. Umbach, D. Beljonne, J. Cornil, Jean-Luc Bredas

Research output: Contribution to journalArticlepeer-review

61 Scopus citations

Abstract

Interchain interactions in organic conjugated solids causes a splitting of the lowest excited electronic states which depends on the relative packing of the chromophores and on the conjugation length. The splitting (also known as Davydov splitting) was measured for the first time in a model compound (α-sexithienyl), but the question remained open on how the Davydov splitting depends on the conjugation length. This question is particularly important because the relative location of the excitonic components plays a major role in determining the photophysics of the systems. We have therefore measured the Davydov splitting of the lowest 1 1Bu exciton in the model systems of α-quaterthienyl (T4) and α-sexithienyl (T6) from the low-temperature polarized absorption of oriented single crystals. Due to the very similar crystal structure of the two materials, the change in exciton splitting can be directly related to the different molecular wave-function delocalization over the chain. Here we show that the Davydov splitting of the lowest exciton decreases as the molecular wave-function delocalization increases. This result, which contradicts the dipole model expectations, is confirmed by correlated quantum-chemical calculations. In addition, we predict the size of the interchain interactions in the polymer where a direct optical measurement is precluded by the intrinsic molecular disorder.

Original languageEnglish (US)
Pages (from-to)6296-6300
Number of pages5
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume62
Issue number10
DOIs
StatePublished - Sep 1 2000

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics

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