Conformational disorder of conjugated polymers

Westenhoff, Sebastian; Beenken, Wichard J. D.; Yartsev, Arkady; Greenham, Neil C.

doi:10.1063/1.2358682

Cited by 63 publications

(84 citation statements)

References 37 publications

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“…This suggests that the increase of conformational disorder in the partially collapsed chains reduces the efficiency of intrachain energy transfer. 9,14,36,37 The emission of high-energy chromophores in MEH-PPV was also observed in our previous studies, which investigated the polymer solutions in various alcohol solvents. 20,21 However, the emission occurred at lower energy region.…”

Section: Resultsmentioning

confidence: 83%

Solvent-induced photoemissions of high-energy chromophores of conjugated Polymer MEH-PPV: Role of conformational disorder

Traiphol

Charoenthai

2008

Macromol. Res.

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This study examined the photoemission behaviors of isolated chains of poly[2-methoxy, 5-(2'-ethylhexyloxy)-1,4-phenylenevinylene](MEH-PPV) dispersed in various solvents including dichloromethane, chloroform and tetrahydrofuran(THF). A change in polymer-solvent interactions in these solutions caused the MEH-PPV chains to adopt different local conformations, which in turn affected their radiative de-excitation pathways. For the polymer in dichloromethane and chloroform, in which the conjugated chains are relatively extended, photoemission occurs mostly at the long chromophores with lowest HOMO-LUMO energy gap. Their emission spectra showed a main peak at ~560 nm. Dual photoemission of high-and low-energy chromophores was observed when the conjugated chains were forced to partially collapse in a poor solvent THF. Novel high-energy peaks and a typical low-energy peak were detected at ~414 nm and ~554 nm, respectively. The observation of the high-energy peaks indicates significant suppression of the intrachain energy transfer process, which was attributed to the increase in conformational disorder in the partially collapsed coils. An analysis of the excitation spectra suggests that the high-energy peaks belong to short chromophores constituting of one or two repeat units. This study systematically investigated the effects of polymer concentration, temperature and single bond defects along the backbone on the photoemission of the high-energy chromophores.

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Section: Resultsmentioning

confidence: 83%

Solvent-induced photoemissions of high-energy chromophores of conjugated Polymer MEH-PPV: Role of conformational disorder

Traiphol

Charoenthai

2008

Macromol. Res.

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“…A time dependence of the diffusion coefficient is expected to be observed in the first few picoseconds or even sub-picoseconds after excitation. [5,20,21] and following this scenario t 40 would be the tail of such a regime into our time-window. Since under our time resolution the importance of this component is almost insignificant, less than 5 %, it is not going to be considered on the following analysis.…”

Section: Time-resolved Fluorescence Decays Of Pfsmentioning

confidence: 99%

Exciton Diffusion in Polyfluorene Copolymer Thin Films: Kinetics, Energy Disorder and Thermally Assisted Hopping

Dias

Kamtekar²,

Cazati

et al. 2009

ChemPhysChem

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A series of {(9,9-dioctylfluorene)(0.7-x)-(dibenzothiophene-S,S-dioxide)(0.3)-[4,7-bis(2-thienyl)-2,1,3-benzothiadiazole](x)} (PFS(30)-TBTx), where x represents the minor percentage of the red emitter 4,7-bis(2-thienyl)-2,1,3-benzothiadiazole (TBT) randomly incorporated into the copolymer backbone, is investigated in order to follow the energy transfer from PFS(30) to TBT moieties. The emission of the donor poly[(9,9-dioctylfluorene)(0.7)-(dibenzothiophene-S,S-dioxide)(0.3) identified by PFS(30) and peaking at 450 nm, is clearly quenched by the presence of the red TBT chromophore emitting at 612 nm, with an isoemissive point observed when the spectra are collected as a function of temperature. A plot of the ratio between the TBT and PFS(30) emissions as a function of the reciprocal of temperature gives a clear linear trend between 290 and 200 K, with an activation energy of 20 meV and showing a turn over to a non-activated regime below 200 K. Picosecond time-resolved fluorescence decays collected at the PFS(30) and TBT emission wavelengths, show a decay of the PFS(30) emission and a fast build-in, followed by a decay, of the TBT emission, confirming that the population of the TBT excited state occurs during the PFS(30) lifetime (approximately 600 ps). The population of the TBT excited state occurs on a time regime around 150 ps at 290 K, showing an energy barrier of 20 meV that turns over to a non-activated regime below 200 K in clear agreement with the steady-state data. The origin of the activation barrier is attributed to the presence of physical and energetic disorder, affected by fast thermal fluctuations that dynamically change the energy landscape and control the exciton migration through the polymer density of states.

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“…Several experimental methods were suggested for determination of the exciton diffusion coefficient and diffusion radius, but none of them is universal and provides the full picture. 3 The main methods proposed for conjugated polymers are exciton quenching by deliberately added quenching centers [4][5][6][7] or by the presence of metal, 8 fluorescence and transient absorption depolarization, [9][10][11][12][13] fluorescence and transient absorption spectral changes associated with downhill energy transfer ͑spectral migration͒, 10,14-16 and exciton-exciton annihilation. 17 The polarization decay in combination with spectral migration gives information about the very initial exciton diffusion events, and it depends on the exciton hopping rate as well as on the short-range order of the polymer chains.…”

Section: Introductionmentioning

confidence: 99%

Exciton diffusion and relaxation in methyl-substituted polyparaphenylene polymer films

Gulbinas¹,

Mineviciūte²,

Hertel

et al. 2007

The Journal of Chemical Physics

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Exciton diffusion in ladder-type methyl-substituted polyparaphenylene film and solution was investigated by means of femtosecond pump-probe spectroscopy using a combined approach, analyzing exciton-exciton annihilation, and transient absorption depolarization properties. We show that the different views on the exciton dynamics offered by anisotropy decay and annihilation are required in order to obtain a correct picture of the energy transfer dynamics. Comparison of the exciton diffusion coefficient and exciton diffusion radius obtained for polymer film with the two techniques reveals that there is substantial short-range order in the film. Also in isolated chains there is considerable amount of order, as revealed from only partial anisotropy decay, which shows that only a small fraction of the excitons move to differently oriented polymer segments. It is further concluded that interchain energy transfer is faster than intrachain transfer, mainly as a result of shorter interchain distances between chromophoric units.

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Conformational disorder of conjugated polymers

Cited by 63 publications

References 37 publications

Solvent-induced photoemissions of high-energy chromophores of conjugated Polymer MEH-PPV: Role of conformational disorder

Solvent-induced photoemissions of high-energy chromophores of conjugated Polymer MEH-PPV: Role of conformational disorder

Exciton Diffusion in Polyfluorene Copolymer Thin Films: Kinetics, Energy Disorder and Thermally Assisted Hopping

Exciton diffusion and relaxation in methyl-substituted polyparaphenylene polymer films

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