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Issue 23, 2010
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Association function of conjugated polymer charge-transfer complex

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The donor–acceptor ground-state charge-transfer complex (CTC) formed in solution between a conjugated polymer, poly[methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene-vinylene] (MEH-PPV), and a low-molecular-weight organic acceptor, 2,4,7-trinitrofluorenone (TNF), is studied by optical absorption and Raman spectroscopy. The CTC absorption as a function of TNF content shows a threshold increase that is in conflict with the model commonly used for optical characterization of low-molecular-weight CTCs. The shift of MEH-PPV characteristic Raman band at 1585 cm−1 also exhibits a threshold dependence upon TNF addition. We assign the threshold in both the absorption and Raman data to the CTC concentration. To describe the threshold in the terms of the common model, we extend it by introducing an association function instead of a constant. The association function of acceptor concentration has been calculated to be Ka ∼ 1.5–3 M−1 below the threshold, to increase steeply up to Ka ∼ 6–7.5 M−1 just after the threshold, and then to grow gradually up to Ka ∼ 40 M−1. The CTC molar absorption coefficient has been found to be εCTC = (12.7 ± 0.6) × 103 M−1 cm−1 at 635 nm. We explain the threshold as a result of the positive feedback: the CTC formation induces planarizaton of conjugated polymer segments that in turn facilitates further CTC formation.

Graphical abstract: Association function of conjugated polymer charge-transfer complex

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The article was received on 04 Jan 2010, accepted on 04 Mar 2010 and first published on 15 Apr 2010

Article type: Paper
DOI: 10.1039/B927324G
Citation: Phys. Chem. Chem. Phys., 2010,12, 6021-6026
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    Association function of conjugated polymer charge-transfer complex

    O. D. Parashchuk, V. V. Bruevich and D. Yu. Paraschuk, Phys. Chem. Chem. Phys., 2010, 12, 6021
    DOI: 10.1039/B927324G

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