Origin of line broadening in the electronic absorption spectra of conjugated polymers: Three-pulse-echo studies of MEH-PPV in toluene

Gregory D. Scholes, Delmar S. Larsen, Graham R. Fleming, Gary Rumbles, Paul L. Burn

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Abstract

Integrated three-pulse stimulated echo peak shift data are compared for N,N-bis-dimethylphenyl-2,4,6,8-perylenetetracarbonyl diamide and poly[2-(2′-ethylhexyloxy)-5-methoxy-1,4-phenylenevinylene] (MEH-PPV) in toluene solvent. These two molecules represent a model probe of solvation dynamics and a prototypical soluble, electroluminescent conjugated polymer, respectively. The results indicate that it is inappropriate to describe the linear absorption spectrum of MEH-PPV as being primarily inhomogeneously broadened. Conformational disorder along the polymer backbone gives rise to an ensemble of polyene electronic oscillator's that are strongly coupled to each other. As a consequence, fluctuations in the electronic energy gap on a time-scale of 50-fs derive primarily from bath-mediated exciton scattering. The data reported here provide an explanation for the broad, structureless electronic absorption of MEH-PPV. This interpretation provides a valuable insight into the nature of the initial photoexcited state, and the efficient population of the emissive state.

Original languageEnglish
Pages (from-to)13670-13678
Number of pages9
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume61
Issue number20
Publication statusPublished - May 15 2000

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ASJC Scopus subject areas

  • Condensed Matter Physics

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