Ground state of π-conjugated polymer chains forming an intermolecular charge-transfer complex as probed by Raman spectroscopy

Bruevich, Vladimir V.; Makhmutov, T. Sh.; Елизаров, С.Г.; Nechvolodova, E. M.; Paraschuk, Dmitry Yu.

doi:10.1134/s1063776107090014

Cited by 9 publications

(11 citation statements)

References 26 publications

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“…Planarization of the polymer chains and formation of crystalline domains are but two examples. Such properties are closely related to charge delocalization over conjugated polymer chains (nonexisting in small-molecule CTCs) so that the electron density from several repeating units of the polymer is transferred to an acceptor molecule. , …”

Section: Introductionmentioning

confidence: 99%

Charge Transfer Dynamics in Donor–Acceptor Complexes between a Conjugated Polymer and Fluorene Acceptors

et al. 2014

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 2 compared with those from Density Functional Theory calculations. The charge transfer dynamics are studied using an ultrafast visible-pump -IR-probe photoinduced absorption technique. We demonstrate that the acceptor EA is the key -but not the only -parameter that governs charge recombination rates that scale exponentially with the acceptor EA. From the time-resolved data we deduced a model that describes charge dynamics for acceptors with low and high EAs. The two opposite trends -higher acceptor EA increases the driving force for charge separation but also inevitably increases the rate of undesirable charge recombination -should be carefully counterbalanced in designing of novel polymer-fullerene bulk heterojunctions.

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Section: Introductionmentioning

confidence: 99%

Charge Transfer Dynamics in Donor–Acceptor Complexes between a Conjugated Polymer and Fluorene Acceptors

et al. 2014

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“…5-7 units in MEH-PPV 7,52,53 ) is also affected by complexation. 16,54 Specifically, using Raman spectroscopy, the CTC formation was shown to increase the chain planarity and torsional rigidity 16,55 that can be explained by more quinoid character of the complexed polymer chain, which is stiffer and more planar. The NE can then be attributed to the two mechanisms: steric and/or electronic.…”

Section: Microscopic Picture Of the Neighbor Effectmentioning

confidence: 99%

Threshold-like complexation of conjugated polymers with small molecule acceptors in solution within the neighbor-effect model

Sosorev

Parashchuk

Zapunidi

et al. 2016

Phys. Chem. Chem. Phys.

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In some donor-acceptor blends based on conjugated polymers, a pronounced charge-transfer complex (CTC) forms in the electronic ground state. In contrast to small-molecule donor-acceptor blends, the CTC concentration in polymer:acceptor solution can increase with the acceptor content in a threshold-like way. This threshold-like behavior was earlier attributed to the neighbor effect (NE) in the polymer complexation, i.e., next CTCs are preferentially formed near the existing ones; however, the NE origin is unknown. To address the factors affecting the NE, we record the optical absorption data for blends of the most studied conjugated polymers, poly(2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV) and poly(3-hexylthiophene) (P3HT), with electron acceptors of fluorene series, 1,8-dinitro-9,10-antraquinone (), and 7,7,8,8-tetracyanoquinodimethane () in different solvents, and then analyze the data within the NE model. We have found that the NE depends on the polymer and acceptor molecular skeletons and solvent, while it does not depend on the acceptor electron affinity and polymer concentration. We conclude that the NE operates within a single macromolecule and stems from planarization of the polymer chain involved in the CTC with an acceptor molecule; as a result, the probability of further complexation with the next acceptor molecules at the adjacent repeat units increases. The steric and electronic microscopic mechanisms of NE are discussed.

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“…46 However, several vibrational modes are considerably shifted in frequency, and it is well established that these shifts of donor and acceptor frequencies are related to the occurrence of a ground state charge transfer. 48,[50][51][52][53][54] In particular, for the acceptor, TNF, a redshift of the C=O stretching mode has been observed in ground state CT complexes and is related to an increase in the electron density resulting from partial ground-state CT. 48,52 In the HAT6-TNF spectrum, the C=O mode is observed to have redshifted to 1730 cm −1 . Based on the data in literature 52 it is estimated that the shift of 3 cm −1 corresponds to an increase in electron density on TNF of about 0.03 e − .…”

Section: B Raman Spectroscopymentioning

confidence: 99%

“…30,31 But in contrast, there are only a few reports on intermolecular ground-state CT in large molecular complexes, most of them involving polymers doped with an strong electron acceptor. 53,62 For discotic liquid crystalline compounds, involving D-A interaction, it is generally accepted that intermolecular charge transfer occurs in the excited state, but not in the ground state. 27,28 However, we have found strong indications for a weak ground-state electron transfer in the HAT6-TNF complex.…”

Section: B Raman Spectroscopymentioning

confidence: 99%

Electronic and vibronic properties of a discotic liquid-crystal and its charge transfer complex

Haverkate

Zbiri

Johnson

et al. 2014

The Journal of Chemical Physics

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Discotic liquid crystalline (DLC) charge transfer (CT) complexes combine visible light absorption and rapid charge transfer characteristics, being favorable properties for photovoltaic (PV) applications. We present a detailed study of the electronic and vibrational properties of the prototypic 1:1 mixture of discotic 2,3,6,7,10,11-hexakishexyloxytriphenylene (HAT6) and 2,4,7-trinitro-9-fluorenone (TNF). It is shown that intermolecular charge transfer occurs in the ground state of the complex: a charge delocalization of about 10 −2 electron from the HAT6 core to TNF is deduced from both Raman and our previous NMR measurements (2012)], implying the presence of permanent dipoles at the donor-acceptor interface. A combined analysis of density functional theory calculations, resonant Raman and UV-VIS absorption measurements indicate that fast relaxation occurs in the UV region due to intramolecular vibronic coupling of HAT6 quinoidal modes with lower lying electronic states. Relatively slower relaxation in the visible region the excited CT-band of the complex is also indicated, which likely involves motions of the TNF nitro groups. The fast quinoidal relaxation process in the hot UV band of HAT6 relates to pseudo-Jahn-Teller interactions in a single benzene unit, suggesting that the underlying vibronic coupling mechanism can be generic for polyaromatic hydrocarbons. Both the presence of ground state CT dipoles and relatively slow relaxation processes in the excited CT band can be relevant concerning the design of DLC based organic PV systems.

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Ground state of π-conjugated polymer chains forming an intermolecular charge-transfer complex as probed by Raman spectroscopy

Cited by 9 publications

References 26 publications

Charge Transfer Dynamics in Donor–Acceptor Complexes between a Conjugated Polymer and Fluorene Acceptors

Charge Transfer Dynamics in Donor–Acceptor Complexes between a Conjugated Polymer and Fluorene Acceptors

Threshold-like complexation of conjugated polymers with small molecule acceptors in solution within the neighbor-effect model

Electronic and vibronic properties of a discotic liquid-crystal and its charge transfer complex

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