Fluorescence yield and lifetime of isolated polydiacetylene chains: Evidence for a one-dimensional exciton band in a conjugated polymer

Lécuiller, R.; Berréhar, J.; Ganière, Jean‐Daniel; Lapersonne‐Meyer, C.; Lavallard, P.; Schott, M.

doi:10.1103/physrevb.66.125205

Cited by 64 publications

(111 citation statements)

References 11 publications

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“…1D). In PDA, for example, the most extended chains show a dramatic increase of 0-0 transition oscillator strength relative to the 0-1 peak at low temperature, because the extended π-system constitutes an effective linear J-aggregate (43). It is conceivable that exciton self-trapping limits excitonic coherence and thus the transfer of oscillator strength to the purely electronic (0-0) transition.…”

Section: Discussionmentioning

confidence: 99%

“…in this study to be the most heterogeneous polymeric material studied to date on the single-chromophore level, with the excitonic single-chromophore picture (36)(37)(38) established for the most ordered polymers such as polyfluorenes (39) (PF), ladder-type poly(para-phenylenes) (40, 41) (LPPP), polydiacetylene (42,43) (PDA), and poly(phenylene-ethynylene) (28) (PPE). On the level of single chromophores, P3HT behaves like other prominent materials, such as poly(phenylene-vinylenes) (41, 44) (PPVs), with the exception of exhibiting giant variability in transition wavelengths spanning almost 200 nm.…”

Section: Significancementioning

confidence: 99%

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Unraveling the chromophoric disorder of poly(3-hexylthiophene)

Thiessen

Vogelsang

Adachi

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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The spectral breadth of conjugated polymers gives these materials a clear advantage over other molecular compounds for organic photovoltaic applications and is a key factor in recent efficiencies topping 10%. However, why do excitonic transitions, which are inherently narrow, lead to absorption over such a broad range of wavelengths in the first place? Using single-molecule spectroscopy, we address this fundamental question in a model material, poly(3-hexylthiophene). Narrow zero-phonon lines from single chromophores are found to scatter over 200 nm, an unprecedented inhomogeneous broadening that maps the ensemble. The giant red shift between solution and bulk films arises from energy transfer to the lowest-energy chromophores in collapsed polymer chains that adopt a highly ordered morphology. We propose that the extreme energetic disorder of chromophores is structural in origin. This structural disorder on the single-chromophore level may actually enable the high degree of polymer chain ordering found in bulk films: both structural order and disorder are crucial to materials physics in devices.structure-property relations | conformational disorder | photophysics | organic solar cells D espite half a century of research into organic photovoltaics (1), the promise of versatile paint-on solar-cell modules based on conjugated polymers has prompted a present flurry of activity in the field (2-5). A particular appeal of such excitonic solar cells is that very little material is needed to efficiently absorb light. This is due to the fact that the oscillator strength of primary photoexcitations, electron-hole pairs with binding energies far exceeding kT, is focused in the excitonic transition. The obvious downside is that this concentration also means excitonic transitions are inherently narrow and usually offer only mediocre spectral overlap with the broad solar spectrum. How then can excitonic solar cells be designed with appropriate spectral breadth? Merely introducing energetic disorder in the underlying excitonic material should lead to low-energy traps, impeding charge harvesting.Although the optical and electronic properties of conjugated polymers are not perfectly suited to photovoltaics, their absorption spectra are surprisingly broad despite the excitonic nature of the transitions. Moreover, the diversity in functional characteristics revealed by varying processing conditions has fueled the quest to formulate robust structure-property relationships between the electronic and optical properties and the underlying polymer structure (6-12). Polythiophene derivatives have evolved into one of the chosen workhorse materials for solar-cell research (13,14). Early spectroscopic studies established extraordinary solvatochromic and thermochromic characteristics, which were attributed to large conformational changes in response to the immediate environment (15-17). It is little surprise then that such diversity in device characteristics exists when using these materials (4). Poly(3-hexylthiophene) (P3HT) (structure show...

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Section: Discussionmentioning

confidence: 99%

Section: Significancementioning

confidence: 99%

Unraveling the chromophoric disorder of poly(3-hexylthiophene)

Thiessen

Vogelsang

Adachi

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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“…1.d). These experimental facts show that the emission spatial profile is characteristic of the chain and is established very rapidly, on a timescale short compared to the 90 ps exciton effective lifetime 8 .…”

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confidence: 88%

“…Their optical excitation, an exciton, is usually considered as a neutral excited state of the chain 10 . However, a one dimensional excitonic energy band is necessary to account for polydiacetylenes optical properties 7,8 .…”

mentioning

confidence: 99%

Macroscopic coherence of a single exciton state in an organic quantum wire

et al. 2005

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“…26,27 In such excitons, the electron and hole are bound over several unit cells. A compelling example of this limit is provided by isolated, extended chains of red-phase polydiacetylene derivatives, 27 which show ultra narrow photoluminescence linewidths and superradiance [28][29][30] characteristic of J-aggregates at low temperature. 31 The work by Niles et al 1 therefore demonstrates that in regioregular P3HT films, there is a competition between J-like (intrachain) and H-like (interchain) excitonic coupling.…”

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confidence: 99%

Two-dimensional spatial coherence of excitons in semicrystalline polymeric semiconductors: Effect of molecular weight

et al. 2013

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The electronic properties of macromolecular semiconductor thin films depend profoundly on their solid-state microstructure, which in turn is governed, among other things, by the processing conditions selected and the polymer's chemical nature and molecular weight. Specifically, lowmolecular-weight materials form crystalline domains of cofacially π-stacked molecules, while the usually entangled nature of higher molecular-weight polymers leads to microstructures comprised of molecularly ordered crystallites interconnected by amorphous regions. Here, we examine the interplay between extended exciton states delocalized along the polymer backbones and across polymer chains within the π-stack, depending on the structural development with molecular weight.Such two-dimensional excitations can be considered as Frenkel excitons in the limit of weak intersite coupling. We combine optical spectroscopies, thermal probes, and theoretical modeling, focusing on neat poly(3-hexylthiophene) (P3HT) -one of the most extensively studied polymer semiconductors -of weight-average molecular weight (M w ) of 3-450 kg/mol. In thin-film structures of high-molecular-weight materials (M w > 50 kg/mol), a balance of intramolecular and intermolecular excitonic coupling results in high exciton coherence lengths along chains (~4 thiophene units), with interchain coherence limited to ~2.5 chains. In contrast, for structures of low-M w P3HT (<40 kg/mol), the interchain exciton coherence is dominant (~20% higher than in architectures formed by high-molecular-weight materials). In addition, the spatial coherence within the chain is significantly reduced (by nearly 30%). These observations give valuable structural information; they suggest that the macromolecules in aggregated regions of high-molecular-weight P3HT adopt a more planar conformation compared to low-molecular-weight materials. This results in the observed increase in intrachain exciton coherence. In contrast, shorter chains seem to lead to torsionally more disordered architectures. A rigorous, fundamental description of primary photoexcitations in π-conjugated polymers is hence developed: two-dimensional excitons are defined by the chain-length dependent molecular arrangement and interconnectivity of the conjugated macromolecules, leading to interplay between intramolecular and intermolecular spatial coherence.

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Fluorescence yield and lifetime of isolated polydiacetylene chains: Evidence for a one-dimensional exciton band in a conjugated polymer

Cited by 64 publications

References 11 publications

Unraveling the chromophoric disorder of poly(3-hexylthiophene)

Unraveling the chromophoric disorder of poly(3-hexylthiophene)

Macroscopic coherence of a single exciton state in an organic quantum wire

Two-dimensional spatial coherence of excitons in semicrystalline polymeric semiconductors: Effect of molecular weight

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