Ultrafast excitation transfer and trapping in a thin polymer film

Grage, Mette M.-L.; Zaushitsyn, Yuri; Yartsev, Arkady; Chachisvilis, Mirianas; Sundström, Villy; Pullerits, Tõnu

doi:10.1103/physrevb.67.205207

Cited by 113 publications

(157 citation statements)

References 33 publications

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“…The ultrafast changes in the TA spectra and the dynamics of vibrational wave packets in polydiacetylene have been explained in terms of the geometrical relaxation of a free exciton to a self-trapped state within 100 fs. 40 In addition, ϳ30 fs depolarization component was observed in the stimulated emission signal from amorphous films of polythiophene, 41 which could not be explained by incoherent hopping and may also represent a signature of dynamic localization. All these observations suggest that structural relaxation and dynamic localization phenomena are common in conjugated polymers.…”

Section: Discussionmentioning

confidence: 99%

Ultrafast depolarization of the fluorescence in a conjugated polymer

et al. 2005

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The effect of the extent of electron conjugation on the primary photophysics in semiconducting polymers is reported. A rapid depolarization of photoluminescence and transient absorption, which indicates a reorientation of the transition dipole moment by ϳ30°on a sub-100 fs time scale, is observed in the fully conjugated polymer poly͓2-͑2'-ethylhexyloxy͒-5-methoxy-1,4-phenylenevinylene͔ ͑MEH-PPV͒. In contrast, partially conjugated polymers exhibit a much slower depolarization. The results reveal rapid changes of exciton delocalization in the fully conjugated MEH-PPV driven by structural relaxation.

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Section: Discussionmentioning

confidence: 99%

Ultrafast depolarization of the fluorescence in a conjugated polymer

et al. 2005

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“…Time-resolved emission studies, Monte Carlo simulations, and ultrafast transient absorption polarization measurements have been carried out to investigate the phenomenon in PPV, 35,39,43-46 MEH-PPV and derivatives, 57,58 polyfluorene, 80 rigid stepladder type copolymers, 81 and a polythiophene polymer. 77,78 Time scales ranging from subpicoseconds to hundreds of picoseconds were reported, so that we conclude that exciton hopping contributes to the three time scales (∼500 fs, ∼5 ps, ∼50 ps) of the spectral relaxation observed here for PCDTBT in solution and film. The fastest one-step hops occur in 0.5-1 ps, in agreement with literature, and then cascading and decelerating energy migration leads to the observed progressive red shift of the emission spectrum.…”

Section: Relaxation Of the Emission Spectrum Following Smentioning

confidence: 98%

Exciton Formation, Relaxation, and Decay in PCDTBT

et al. 2010

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Abstract:The nature and time evolution of the primary excitations in the pristine conjugated polymer, PCDTBT, are investigated by femtosecond-resolved fluorescence up-conversion spectroscopy. The extensive study includes data from PCDTBT thin film and from PCDTBT in chlorobenzene solution, compares the fluorescence dynamics for several excitation and emission wavelengths, and is complemented by polarization-sensitive measurements. The results are consistent with the photogeneration of mobile electrons and holes by interband π-π* transitions, which then self-localize within about 100 fs and evolve to a bound singlet exciton state in less than 1 ps. The excitons subsequently undergo successive migrations to lower energy localized states, which exist as a result of disorder. In parallel, there is also slow conformational relaxation of the polymer backbone. While the initial self-localization occurs faster than the time resolution of our experiment, the exciton formation, exciton migration, and conformational changes lead to a progressive relaxation of the inhomogeneously broadened emission spectrum with time constants ranging from about 500 fs to tens of picoseconds. The time scales found here for the relaxation processes in pristine PCDTBT are compared to the time scale (<0.2 ps) previously reported for photoinduced charge transfer in phaseseparated PCDTBT:fullerene blends (Phys. Rev. B 2010, 81, 125210). We point out that exciton formation and migration in PCDTBT occur at times much longer than the ultrafast photoinduced electron transfer time in PCDTBT:fullerene blends. This disparity in time scales is not consistent with the commonly proposed idea that photoinduced charge separation occurs after diffusion of the polymer exciton to a fullerene interface. We therefore discuss alternative mechanisms that are consistent with ultrafast charge separation before localization of the primary excitation to form a bound exciton.

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“…8 and references therein). When R = d there is a significant error in the line-dipole approximation result.…”

Section: Validity Of the Line-dipole Approximationmentioning

confidence: 99%

“…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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Ultrafast excitation transfer and trapping in a thin polymer film

Cited by 113 publications

References 33 publications

Ultrafast depolarization of the fluorescence in a conjugated polymer

Ultrafast depolarization of the fluorescence in a conjugated polymer

Exciton Formation, Relaxation, and Decay in PCDTBT

Exciton transfer integrals between polymer chains

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