Abstract
In this study, electroabsorption (Stark) spectroscopy is used to determine the trace of the change in polarizability (tr ) 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 of ∼2000 A3 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 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 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...
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