Ground State of frame0-Conjugated Polymer Chains Forming
an Intermolecular Charge-Transfer Complex
As Probed by Raman Spectroscopy

V. V. Bruevicha, T. Sh. Makhmutova, S. G. Elizarova,
E. M. Nechvolodovab, and D. Yu. Paraschuka*

a International Laser Center, Moscow State University, Vorob’evy gory, Moscow, 119992 Russia

* e-mail: paras@polys.phys.msu.ru

b Semenov Institute of Chemical Physics, Russian Academy of Sciences, ul. Kosygina 4, Moscow, 119991 Russia

Received January 9, 2007

Abstract—The intermolecular charge-transfer complex (CTC) between the conjugated polymer MEH-PPV
and the low-molecular organic acceptor trinitrofluorenone (TNF) has been studied by Raman and optical
absorption spectroscopy. On mixing MEH-PPV with TNF, an absorption band due to the CTC appeared in the
optical gap of the polymer, whereas, in the Raman spectra, characteristic bands of the polymer are shifted and
their widths and intensities change. The low-frequency shift of the strongest band at 1580 cm–1 in the Raman
spectrum of the polymer, assigned to the symmetric stretching vibration of the phenyl group, is shown to be due
to electron density transfer from the -conjugated system of the polymer to the acceptor and is as large as 5 cm–1,
which corresponds to a charge transfer on the order of 0.1e–. Even at a low acceptor concentration (one TNF
molecule per 10 monomer units of the polymer), most Raman-active conjugated chains are involved in the CTC.
It is suggested that conjugated segments of the polymer can form a CTC of variable composition MEH-PPV :
TNF = 1 : X, where 0.1 < equal X < equal 0.5 (for each monomer unit of the polymer), and one TNF molecule can thereby
interact with two conjugated segments of MEH-PPV. The conjugated polymer chains involved in the CTC can
become more planar, and their interaction with the local environment can noticeably change; however, their
conjugation length, most likely, remains unaltered.

PACS numbers: 82.35.Cd, 78.30.Jw, 78.40.Me

DOI: 10.1134/S1063776107090014

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