The effects of structural and microenvironmental disorder on the electronic properties of poly[2-methoxy,5-(2′-ethyl-hexoxy)-1,4-phenylene vinylene] (MEH-PPV) and related oligomers

Sebastian Wachsmann-Hogiu, Linda A. Peteanu, Limin Angela Liu, David J. Yaron, Jurjen Wildeman

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36 Scopus citations

Abstract

In this study, electroabsorption (Stark) spectroscopy is used to determine the trace of the change in polarizability (tr Δα) and the absolute value of the change in dipole moment (|Δμ|) of the electroluminescent polymer poly[2-methoxy,5-(2′-ethyl-hexoxy)-1,4-phenylene vinylene] (MEH-PPV) and several model oligomers in solvent glass matrixes. We find a value of tr Δα of ∼2000 Å3 for the polymer and for a 9-ring substituted oligomer in both toluene and 2-methyl tetrahydrofuran matrixes at 77 K with smaller values being obtained for 3- and 5-ring unsubstituted oligomers. Although gas-phase calculations of tr Δα using INDO/SCI yield values that are about a factor of 8 smaller than the experiment, excellent agreement is obtained when the effects of solid-state dielectric screening are included. Screening increases tr Δα by bringing the energy gap between the 1Bu and mAg states into agreement with solid-state measurements. Substantial values of |Δμ| are observed experimentally both for the polymer and for the oligomers (6-11 D). Because in a planar (C2h) geometry the oligomer and polymer are centrosymmetric, the observed |Δμ| is an indication of disorder-induced symmetry breaking in the material. Calculations indicate that disorder in the ground-state geometry of the polymer (inner-sphere disorder) can account for nearly half of the observed |Δμ|. Disorder in the glassy environment (outer-sphere disorder) leads to a nonuniform electrostatic environment, and calculations show that this is a substantial contributor, accounting for the remainder of the observed |Δμ|.

Original languageEnglish (US)
Pages (from-to)5133-5143
Number of pages11
JournalJournal of Physical Chemistry B
Volume107
Issue number22
StatePublished - Jun 5 2003

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

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