Raman photoselection and conjugation-length dispersion in conjugated polymer solutions

Shand, M. L.; Chance, R. R.; Lepostollec, M.; Schott, M.

doi:10.1103/physrevb.25.4431

Cited by 101 publications

(55 citation statements)

References 14 publications

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“…S4). This similarity in spectral form strongly suggests that the narrow lines observed over such a broad spectral range arise from isolated chromophores (38). Because narrow single-chromophore zero-phonon lines are observed as far to the red as 680 nm, we conclude that the high-energy side of the bulk spectrum (Fig.…”

Section: Resultsmentioning

confidence: 86%

“…Nevertheless, conventional incremental materials development risks being impeded by lack of a robust understanding of primary photoexcitations in these systems. Is the primary photophysics of polythiophenes dominated by intermolecular interactions and H-aggregate species, or does the material actually adhere to the established concepts (36,38,41) of intrachain chromophores as derived from a wide range of compounds? Our single-molecule experiments tend to favor the latter notion, while leaving room for features of H-aggregation or other bulk solvation effects in In Zeonex, multiple chromophores emit, leading to only a 20% dip in photodetector coincidence rates.…”

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: Resultsmentioning

confidence: 86%

Section: Discussionmentioning

confidence: 99%

Section: Significancementioning

confidence: 99%

See 1 more Smart Citation

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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“…As discussed above, this indicates that even in samples with no chemical defects, the polymers are disordered into collections of chains with relatively short conjugated segments. 20,21,27,28 We recently demonstrated that cooling overcomes at least some of this disorder and that the temperature dependence of the spectra is consistent with relatively small barriers for twisting about the carbon-carbon single bonds. 19 Room temperature solution spectra of shorter polyenes and carotenoids (N ) 5-15), on the other hand, tend to be vibronically resolved and show smaller red shifts upon cooling.…”

Section: U + Transitions In Di-tert-butyl Polyenes and Polyene Oligomersmentioning

confidence: 99%

“…For example, ν(CdC) shows a 1/N dependence with a long polyene limit of 1440 cm -1 . [26][27][28] In low-resolution spectra, vibronic combinations of ν(C-C) and ν(CdC) coalesce into progressions of what appears to be a single, intermediate frequency of 1300-1400 cm -1 . For example, the absorption spectrum of the N ) 5 oligomer shows vibronic intervals of ∼1400 cm -1 (Figure 3).…”

Section: Hplc Analysis and Purification Of Oligomersmentioning

confidence: 99%

Optical Spectroscopy of Long Polyenes

Christensen¹,

Faksh²,

Meyers³

et al. 2004

J. Phys. Chem. A

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We have synthesized a homologous series of soluble, linearly conjugated oligomers and related polymers using molybdenum alkylidene catalysts. We have developed HPLC procedures to isolate the oligomers according to their chain lengths and have obtained the absorption spectra of the purified oligomers in room temperature solutions and in 77 K glasses. The oligomer absorption spectra are structured and remarkably similar to those of simple polyenes with comparable numbers of conjugated double bonds (N). Furthermore, the electronic origins of the low-energy, strongly allowed 1 1 A g -f 1 1 B u + transitions follow the E(0-0) ) A + B/N behavior previously noted in simple polyenes and carotenoids. Extrapolation of data for oligomers with N ) 3-15 suggests E(0-0) ≈ 14 000 cm -1 (λ ≈ 700 nm) in the long polyene limit. The oligomer spectra exhibit modest red shifts on cooling, suggesting minimal conformational disorder in the room temperature samples. In contrast, the absorption spectrum of the longest soluble polymer (N > 100) in this series undergoes a significant red shift and sharpening upon cooling from 300 to 77 K. This indicates that the room temperature polymer is disordered due to relatively low thermal barriers for torsional motion about carbon-carbon single bonds. Unlike the longer oligomers, the low-temperature absorption of the polymer shows well-defined vibronic structure. The polymerization reactions lead to a distribution of conjugation lengths in the unpurified polymer sample. However, the vibronically resolved, red-shifted absorption at low temperature (λ(0-0) ) 630 nm) indicates that this distribution is dominated by species with very long conjugation lengths. The resolution of the low-temperature spectrum argues that the absorption is due to the superposition of almost identical 1 1 A g -f 1 1 B u + spectra and that all conjugated segments in this sample absorb near the asymptotic limit (1/N ≈ 0).

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Monodisperse Poly(triacetylen)-Stäbe: Synthese eines 11.9 nm langen molekularen Drahtes und direkte Bestimmung der effektiven Konjugationslänge durch UV/Vis- und Raman-Spektroskopie

1999

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Mit 16 C‐C‐Doppel‐ und 32 C‐C‐Dreifachbindungen und einer Länge von 11.9 nm ist ein hexadecameres Poly(triacetylen) (PTA) vom Typ 1 der bisher längste linear π‐konjugierte molekulare Draht, der keine aromatischen Wiederholungseinheiten aufweist. Über eine schnelle und effiziente statistische Entschützungs‐Oligomerisierungs‐Sequenz wurde eine vom Monomer bis zum Hexadecamer reichende Serie von PTA‐Oligomeren 1 hergestellt; die effektive Konjugationslänge, bei der Sättigung der molekularen Eigenschaften auftritt, wurde sowohl UV/Vis‐ als auch Raman‐spektroskopisch zu n = 10 (n = Zahl der Monomereinheiten) bestimmt.

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Raman photoselection and conjugation-length dispersion in conjugated polymer solutions

Cited by 101 publications

References 14 publications

Unraveling the chromophoric disorder of poly(3-hexylthiophene)

Unraveling the chromophoric disorder of poly(3-hexylthiophene)

Optical Spectroscopy of Long Polyenes

Monodisperse Poly(triacetylen)-Stäbe: Synthese eines 11.9 nm langen molekularen Drahtes und direkte Bestimmung der effektiven Konjugationslänge durch UV/Vis- und Raman-Spektroskopie

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