Excitonic coupling in polythiophenes: Comparison of different calculation methods

Beenken, Wichard J. D.; Pullerits, Tõnu

doi:10.1063/1.1636460

Cited by 152 publications

(163 citation statements)

References 36 publications

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“…V F ij is the coupling energy between donor and acceptor chromophores i and j. The most tractable approach to obtain this interaction energy is based on the line-dipole approximation 51,52 , which can show high accuracy at very low calculation cost, with values very close to full quantum chemistry calculations. The simpler point-dipole approximation is not valid here for chromophore separations typical of films.…”

Section: Discussionmentioning

confidence: 99%

Subpicosecond Exciton Dynamics in Polyfluorene Films from Experiment and Microscopic Theory

et al. 2015

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Electronic energy transfer (EET) in organic materials is a key mechanism that controls the efficiency of many processes, including light harvesting antenna in natural and artificial photosynthesis, organic solar cells, and biological systems. In this paper we have examined EET in solid-state thin-films of polyfluorene, a prototypical conjugated polymer with ultrafast photoluminescence experiments and theoretical modelling. We observe EET occurring on a 680 ± 300 fs timescale by looking at the depolarisation of photoluminescence. An * To whom correspondence should be addressed independent, predictive microscopic theoretical model is built by defining 125 000 chromophores containing both spatial and energetic disorder appropriate for a spin-coated thin film. The model predicts time-dependent exciton dynamics, without any fitting parameters, using the incoherent Förster-type hopping model. Electronic coupling between the chromophores is calculated by an improved version of the usual line-dipole model for resonant energy transfer. Without the need for higher level interactions, we yet find that the model is in general agreement with the experimentally observed 680 ± 300 fs depolarisation caused by EET. This leads us to conclude that femtosecond EET in polyfluorene can be well described by conventional resonant energy transfer, as long as the relevant microscopic parameters are well captured. The implications of this finding are that dipole-dipole resonant energy transfer can in some circumstances be fully adequate to describe ultrafast EET without needing to invoke strong or intermediate coupling mechanisms.1

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Section: Discussionmentioning

confidence: 99%

Subpicosecond Exciton Dynamics in Polyfluorene Films from Experiment and Microscopic Theory

et al. 2015

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“…The point-dipole approximation fails to describe energy transfer between large conjugated molecules at short distances, [9][10][11] requiring the use of the line dipole approximation or quantum-mechanical calculations. When this is coupled with the fact that there may be preferential orientation of the polymer chains, particularly when in contact with an interface, the point-dipole approximation to describe layer-to-layer energy transfer appears flawed, but its limitations are not clearly established.…”

Section: Introductionmentioning

confidence: 99%

Distance dependence of excitation energy transfer between spacer-separated conjugated polymer films

2008

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We report a systematic study of the scaling with distance of electronic energy transfer between thin films of conjugated polymers separated by a silica spacer. The energy-transfer kinetics were obtained directly from time-resolved photoluminescence measurements and show a 1 / z 3 distance dependence of the transfer rate between the excited donor and the acceptor film for z Ն 8 nm. This is consistent with Förster theory; but at shorter separations the energy transfer is slower than predicted and can be explained by the breakdown of the point-dipole approximation at z ϳ 5 nm. The results are relevant for organic photovoltaics and light-emitting devices, where energy transfer can provide a means of increasing performance.

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“…In practice, the exact computation of exciton transfer integrals using transition densities is computationally expensive. A convenient approximation is the so-called line-dipole approximation 8,9 , which provides a physically intuitive, yet accurate description for exciton transfer when the chromophore separation is large enough (typically, three or four times the monomer length).…”

Section: Introductionmentioning

confidence: 99%

Exciton transfer integrals between polymer chains

Barford

2007

The Journal of Chemical Physics

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The line-dipole approximation for the evaluation of the exciton transfer integral, J, between conjugated polymer chains is rigorously justified. Using this approximation, as well as the planewave approximation for the exciton center-of-mass wavefunction, it is shown analytically that J ∼ L when the chain lengths are smaller than the separation between them, or J ∼ L −1 when the chain lengths are larger than their separation, where L is the polymer length. Scaling relations are also obtained numerically for the more realistic standing-wave approximation for the exciton center-ofmass wavefunction, where it is found that for chain lengths larger than their separation J ∼ L −1.8 or J ∼ L −2 , for parallel or collinear chains, respectively. These results have important implications for the photo-physics of conjugated polymers and self-assembled molecular systems, as the Davydov splitting in aggregates and the Förster transfer rate for exciton migration decreases with chain lengths larger than their separation. This latter result has obvious deleterious consequences for the performance of polymer photovoltaic devices.

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Excitonic coupling in polythiophenes: Comparison of different calculation methods

Cited by 152 publications

References 36 publications

Subpicosecond Exciton Dynamics in Polyfluorene Films from Experiment and Microscopic Theory

Subpicosecond Exciton Dynamics in Polyfluorene Films from Experiment and Microscopic Theory

Distance dependence of excitation energy transfer between spacer-separated conjugated polymer films

Exciton transfer integrals between polymer chains

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