Enhancing Long-Range Exciton Guiding in Molecular Nanowires by H-Aggregation Lifetime Engineering

Chaudhuri, Debangshu; Li, Dongbo; Che, Yanke; Shafran, Eyal; Gerton, Jordan M.; Zang, Ling; Lupton, John M.

doi:10.1021/nl1033039

Cited by 132 publications

(120 citation statements)

References 30 publications

(67 reference statements)

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“…9 Diffusion lengths exceeding 250 nm were recently attained for a PTCDI nanofiber at room temperature. 10 This length is much longer than those observed for conjugated polymers, usually in the range of a few nanometers. 7 The 1D enhanced exciton diffusion is consistent with the highly polarized emission observed for the same nanofiber; the latter is also directed along the π−π stacking.…”

Section: Accounts Of Chemical Researchmentioning

confidence: 90%

Interfacial Donor–Acceptor Engineering of Nanofiber Materials To Achieve Photoconductivity and Applications

Zang

2015

Acc. Chem. Res.

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Self-assembly of π-conjugate molecules often leads to formation of well-defined nanofibril structures dominated by the columnar π-π stacking between the molecular planes. These nanofibril materials have drawn increasing interest in the research frontiers of nanomaterials and nanotechnology, as the nanofibers demonstrate one-dimensionally enhanced exciton and charge diffusion along the long axis, and present great potential for varying optoelectronic applications, such as sensors, optics, photovoltaics, and photocatalysis. However, poor electrical conductivity remains a technical drawback for these nanomaterials. To address this problem, we have developed a series of nanofiber structures modified with different donor-acceptor (D-A) interfaces that are tunable for maximizing the photoinduced charge separation, thus leading to increase in the electrical conductivity. The D-A interface can be constructed with covalent linker or noncovalent interaction (e.g., hydrophobic interdigitation between alkyl chains). The noncovalent method is generally more flexible for molecular design and solution processing, making it more adaptable to be applied to other fibril nanomaterials such as carbon nanotubes. In this Account, we will discuss our recent discoveries in these research fields, aiming to provide deep insight into the enabling photoconductivity of nanofibril materials, and the dependence on interface structure. The photoconductivity generated with the nanofibril material is proportional to the charge carriers density, which in turn is determined by the kinetics balance of the three competitive charge transfer processes: (1) the photoinduced electron transfer from D to A (also referred to as exciton dissociation), generating majority charge carrier located in the nanofiber; (2) the back electron transfer; and (3) the charge delocalization along the nanofiber mediated by the π-π stacking interaction. The relative rates of these charge transfer processes can be tuned by the molecular structure and nanoscale interface engineering. As a result, maximal photoconductivity can be achieved for different D-A nanofibril composites. The photoconductive nanomaterials thus obtained demonstrate unique features and functions when employed in photochemiresistor sensors, photovoltaics and photocatalysis, all taking advantages of the large, open interface of nanofibril structure. Upon deposition onto a substrate, the intertwined nanofibers form networks with porosity in nanometer scale. The porous structure enables three-dimensional diffusion of molecules (analytes in sensor or reactants in catalysis), facilitating the interfacial chemical interactions. For carbon nanotubes, the completely exposed π-conjugation facilitates the surface modification through π-π stacking in conjunction with D-A interaction. Depending on the electronic energy levels of D and A parts, appropriate band alignment can be achieved, thus producing an electric field across the interface. Presence of such an electric field enhances the charge separation, which may le...

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Section: Accounts Of Chemical Researchmentioning

confidence: 90%

Interfacial Donor–Acceptor Engineering of Nanofiber Materials To Achieve Photoconductivity and Applications

Zang

2015

Acc. Chem. Res.

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“…133 Generally, H-type aggregates of PDIs have been demonstrated to be more suitable for optical applications than Jaggregates. 134 However, although π−π stacking can facilitate Chem. Rev.…”

Section: Linear Optoelectronicsmentioning

confidence: 99%

“…As discovered by Zang et al, 1D nanobelts of N,N′-dicyclohexyl-substituted PDI show persistent strong polarized and self-waveguided fluorescence emission arising from a socalled "flip-flap" stacking morphology. 131,134 Taking additional advantage of steric interactions of rigid p-tert-butylphenoxy substituents at the bay positions, a high electron mobility (1.8 cm 2 V −1 s −1 ) from needle crystals of TBPCHPDI ( Figure 25G,H) was observed, while maintaining strong red fluorescence with a quantum yield of 0.32. 135 The abovementioned work shed light on constructing future fluorescent devices through well-tailored structural design to control the intermolecular π−π interactions.…”

Section: Linear Optoelectronicsmentioning

confidence: 99%

Self-Assembly of Perylene Imide Molecules into 1D Nanostructures: Methods, Morphologies, and Applications

Slattum²,

et al. 2015

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“…However, the signatures of excitonic dimerization, or H-aggregation, are not always straightforward to resolve conclusively (24). H-aggregation should lead to a reduction in radiative rate (25). Typically, upon aggregation of P3HT, a strong decrease in fluorescence quantum yield is observed, but this is accompanied by an increase in fluorescence rate (26) because nonradiative decay rates are also enhanced.…”

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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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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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Enhancing Long-Range Exciton Guiding in Molecular Nanowires by H-Aggregation Lifetime Engineering

Cited by 132 publications

References 30 publications

Interfacial Donor–Acceptor Engineering of Nanofiber Materials To Achieve Photoconductivity and Applications

Interfacial Donor–Acceptor Engineering of Nanofiber Materials To Achieve Photoconductivity and Applications

Self-Assembly of Perylene Imide Molecules into 1D Nanostructures: Methods, Morphologies, and Applications

Unraveling the chromophoric disorder of poly(3-hexylthiophene)

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