Molecular Packing in Unsubstituted Semiconducting Phenylenevinylene Oligomer and Polymer

Hutten, Paul F. van; Wildeman, Jurjen; Meetsma, Auke; Hadziioannou, G

doi:10.1021/ja990934r

Cited by 124 publications

(116 citation statements)

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“…Such molecules pack in a herringbone arrangement with at least 2 molecules in a unit cell. [20][21][22][23] Here, the lower Davydov component ͑alias J-band͒ is weakly allowed along the crystal b direction, 20,[24][25][26] leading to b-polarized superradiant 0-0 emission 27 which diminishes with increasing disorder. [28][29][30][31] In helical MOPVn aggregates, coherence affects the PL spectrum in a manner similar to the ideal linear H-aggregates described above.…”

Section: Introductionmentioning

confidence: 99%

Using circularly polarized luminescence to probe exciton coherence in disordered helical aggregates

Spano

Meskers

Hennebicq

et al. 2008

The Journal of Chemical Physics

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Circularly polarized emission from helical MOPV4 aggregates is studied theoretically based on a Hamiltonian including excitonic coupling, exciton phonon coupling, and site disorder. The latter is modeled via a Gaussian distribution of site energies. The frequency dependence of the circularly polarized luminescence dissymmetry g lum ͑͒ contains structural information about the low-energy-neutral ͑excitonic͒ polaron from which emission originates. Near the 0-0 emission frequency, g lum ͑͒ provides a measure of the exciton coherence length, while at lower energies, in the vicinity of the sideband frequencies, g lum ͑͒ probes the polaron radius. The present work focuses on how the 0-0 dissymmetry, g lum 0-0 , relates to the emitting exciton's coherence function, from which the coherence length is deduced. In the strong disorder limit where the exciton is localized on a single chromophore, g lum 0-0 is zero. As disorder is reduced and the coherence function expands, ͉g lum 0-0 ͉ increases more rapidly than the sideband dissymmetries, resulting in a pronounced surge in g lum ͑͒ near the 0-0 transition frequency. The resulting spectral shape of g lum ͑͒ is in excellent agreement with recent experiments on MOPV4 aggregates. In the limit of very weak disorder, corresponding to the motional narrowing regime, the coherence function extends over the entire helix. In this region, g lum 0-0 undergoes a surprising sign reversal but only for helices which are between n + 1 2 and n + 1 complete turns ͑n =0,1, ...͒. This unusual sign change is due to the dependence of the rotational line strength on long-range exciton coherences which are also responsible for a heightened sensitivity of g lum ͑͒ to long-range excitonic coupling.

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Section: Introductionmentioning

confidence: 99%

Using circularly polarized luminescence to probe exciton coherence in disordered helical aggregates

Spano

Meskers

Hennebicq

et al. 2008

The Journal of Chemical Physics

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“…1c). The unit cell used for the MD simulations and DFT calculations consisted of 12 five-ring oligomers, a total of 816 atoms.Single crystals of PPV oligomers have been grown and structurally characterized [4]. Thin films of the polymer consist of small ordered regions, with a structure similar to that of the crystalline oligomers, separated by disordered regions.…”

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confidence: 99%

“…Figure 1 shows the structure of the five-ring PPV oligomer (Fig. 1a), a crystal [4] of ordered oligomers (Fig. 1b), and an example of a disordered oligomer cluster from the MD simulations (Fig.…”

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Effect of intramolecular disorder and intermolecular electronic interactions on the electronic structure of poly-p-phenylene vinylene

et al. 2007

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We investigate the role of intra-molecular conformational disorder and inter-molecular electronic interactions on the electronic structure of disorder clusters of poly-p-phenylene vinylene (PPV) oligomers. Classical molecular dynamics is used to determine probable molecular geometries, and first-principle density functional theory (DFT) calculations are used to determine electronic structure. Intra-molecular and inter-molecular effects are disentangled by contrasting results for densely packed oligomer clusters with those for ensembles of isolated oligomers with the same intra-molecular geometries. We find that electron trap states are induced primarily by intra-molecular configuration disorder, while the hole trap states are generated primarily from inter-molecular electronic interactions.PACS numbers: 72.80. Le, 71.55.Jr, 71.15.Ej, The emergence of organic electronic devices, including light emitting diodes and field effect transistors, fabricated from conjugated polymers such as poly-pphenylene vinylene (PPV) [1] has stimulated research into the electrical and optical properties of these semiconducting polymers. A theoretical description of these electronic materials is challenging because they are highly disordered and strong interactions between molecules occurring in the condensed phase of the materials are very important in determining their properties. Despite extensive experimental [2] and theoretical research [3], there is still a limited understanding of these strongly interacting disordered materials. In this Letter, we use a combination of classical molecular dynamics (MD) and density functional theory (DFT) to investigate the electronic structure of densely packed clusters of PPV oligomers. Classical MD is used to determine statistically probable molecular geometries for large clusters of PPV oligomers, and DFT calculations are used to determine the electronic structure of the clusters. The effect of intra-molecular configurational disorder and of intermolecular electronic interactions on the electronic structure are disentangled by contrasting the calculated density of states and molecular orbitals for a densely packed oligomer cluster with that for an ensemble of isolated oligomers with the same intra-molecular geometries as the oligomers in the clusters.Statistically probable geometries of disordered clusters of PPV oligomers were simulated using classical MD. To isolate the effect of configurational disorder, we specifically consider clusters of five-ring PPV oligomers as studied experimentally in Ref [4]. Figure 1 shows the structure of the five-ring PPV oligomer (Fig. 1a), a crystal [4] of ordered oligomers (Fig. 1b), and an example of a disordered oligomer cluster from the MD simulations (Fig. 1c). The unit cell used for the MD simulations and DFT calculations consisted of 12 five-ring oligomers, a total of 816 atoms.Single crystals of PPV oligomers have been grown and structurally characterized [4]. Thin films of the polymer consist of small ordered regions, with a structure similar to tha...

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“…The X-ray structural analyses have shown that the central phenyl ring of these OPV derivatives is greatly twisted off from coplanarity with the adjacent phenyl rings [16]. They have also found that the relative position of the side-substituents has a profound effect on the luminescent properties and the single-layer OLED based on unsubstituted 5-phenyl-ring oligomer shows superior device performance compared to that of the octyloxy-side-substituted counterparts [17]. Meier et al have synthesized a series of soluble 2,5-dipropoxy-substituted OPVs containing up to 12-phenyl rings using a combination of the Wittig-Horner, Siegrist, and McMurry reactions [18].…”

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Multifunctional properties of monodisperse end-functionalized oligophenylenevinylenes

Wong

2004

Pure and Applied Chemistry

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Novel series of monodisperse, end-functionalized oligophenylenevinylenes (OPVs) containing up to eight phenyl rings have been designed and synthesized by a convergent approach using the stereoselective Wadsworth-Emmons reactions for an investigation of technologically useful functional properties. According to PM3 semiempirical quantum mechanical calculations, the frontier molecular orbitals and the energy gap of an OPV could be shifted or tuned by the functional substituent(s) that are incorporated as end-caps. Our theoretical and experimental evidences have shown that the end-substituents of an oligomer do not affect coplanarity of the π-conjugated system. It has also been found that the newly synthesized OPVs can exhibit various useful functional properties such as light-emitting properties, photovoltaic effects, third-order nonlinear optical responses, and chemical sensing properties depending on the nature of the end-substituents. In this contribution, the structural factor(s) that can enhance a specific functional property of a molecule or material will be discussed.Poly(phenylenevinylene) (PPV) and its derivatives have been extensively explored and investigated for various technologically useful functional properties in the past two decades because of their potential applications in next-generation optoelectronic and photonic devices. Those properties include electroluminescent response [1], third-order optical nonlinearity [2], photovoltaic property [3], lasing effect [4], and chemical sensing [5]. PPV is the first π-conjugated semiconducting polymer that was used as an emissive material in organic light-emitting diodes (OLEDs) [6], and its derivatives can often exhibit an efficient electroluminescent response [7]. PPV thin-film with a long effective conjugated length was shown to have a large effective nonlinear refractive index, n 2 and a desirable two-photon merit factor, T for all-optical switching and processing [8]. Upon mixing with electron-conducting buckminsterfullerene derivatives, a large photovoltaic response can be obtained [9]. Some PPV derivatives can even show good lasing and interesting chemical sensing properties. Nevertheless, it still remains a challenge for a chemist to further enhance and optimize a specific functional property of a PPV-based material for a practical application as subtle modification of the monomeric unit often leads to a dramatic change in optical and electronic properties of a polymer such as a fluorescence quantum yield and an energy gap. As a result, knowledge of the structure-functional property relationships is fundamentally important for a rational design of efficient and useful PPV-based functional materials. On the other hand, polymers always show structural inhomogeneities and imperfection regardless the method used to prepare them, which would hinder the structure-functional property investigations. Toward the goal of "functional property by design", there is an increasing interest in investigating structure-functional property rela-

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Molecular Packing in Unsubstituted Semiconducting Phenylenevinylene Oligomer and Polymer

Cited by 124 publications

References 44 publications

Using circularly polarized luminescence to probe exciton coherence in disordered helical aggregates

Using circularly polarized luminescence to probe exciton coherence in disordered helical aggregates

Effect of intramolecular disorder and intermolecular electronic interactions on the electronic structure of poly-p-phenylene vinylene

Multifunctional properties of monodisperse end-functionalized oligophenylenevinylenes

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