On the origin of optical activity in polythiophenes

Langeveld-Voss, B.M.W.; Janssen, Raj René; Meijer, E. W.

doi:10.1016/s0022-2860(99)00444-5

Cited by 216 publications

(246 citation statements)

References 69 publications

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“…The spectral shape of g lum ͑͒ in aggregated MOPV4 is peculiar: ͉g lum ͉͑͒ increases steadily with frequency throughout the spectral region encompassing the PL side bands with a sharper increase or surge near the PL origin. A general increase in ͉g lum ͉͑͒ with frequency has also been detected in small chiral molecules 12 and polymers [13][14][15] with thiophene-based chromophores.…”

Section: Introductionmentioning

confidence: 77%

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: 77%

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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“…Normally, -stacked chiral aggregations of conjugated thiophene polymers, as seen in poor solvents, are accompanied by a color change from yellow-orange to purple (5,(9)(10)(11)(12). This change is caused by a transition from a disordered coil-like form to a rod-like, -stacked one to give a chiral supramolecular aggregate with interchain interactions of transoidal PTs.…”

Section: Resultsmentioning

confidence: 99%

“…Chiral PTs normally exhibit optical activity in the -* transition. This phenomenon derives from the main-chain chirality when chains are aggregated to form a supramolecular, -stacked self-assembly due to intermolecular interactions in a poor solvent or at low temperature, whereas they show no activity in the UV-visible region in a good solvent or at high temperatures (5,(9)(10)(11)(12). Recent studies (13)(14)(15)(16), using optically inactive CPs that become chiral after addition of a chiral guest, show that chirality introduction can also be a result of a main-chain chirality, such as a predominantly one-handed helical structure induced by a acidbase complexation between the CP and the chiral guest.…”

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confidence: 99%

Twisting macromolecular chains: Self-assembly of a chiral supermolecule from nonchiral polythiophene polyanions and random-coil synthetic peptides

Nilsson

Rydberg

Baltzer

et al. 2004

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

101

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The self-assembly of a negatively charged conjugated polythiophene derivative and a positively charged synthetic peptide will create a chiral, well ordered supermolecule. This supermolecule has the three-dimensional ordered structure of a biomolecule and the electronic properties of a conjugated polymer. The molecular complex being formed clearly affects the conformation of the polymer backbone. A main-chain chirality, such as a predominantly one-handed helical structure induced by the acid-base complexation between the conjugated polymer and the synthetic peptide, is seen. The alteration of the polymer backbone influences the optical properties of the polymer, seen as changes in the absorption, emission, and Raman spectra of the polymer. The complexation of the polythiophene and the synthetic peptide also induce a change from random-coil to helical structure of the synthetic peptide. The supermolecule described in this article may be used in a wide range of applications such as biomolecular devices, artificial enzymes, and biosensors. T he development of chiral conjugated polymers (CPs) with a well defined structure is of great interest because of their potential for being used in optoelectronic devices, sensors, and catalysis. In particular, polythiophenes (PTs) (1-8) with an optically active substituent in the 3 position have been studied for these purposes. These studies have been focused mainly on the chiral behavior of the PTs depending on solvent (solvatochromism) or temperature (thermochromism). Chiral PTs normally exhibit optical activity in the -* transition. This phenomenon derives from the main-chain chirality when chains are aggregated to form a supramolecular, -stacked self-assembly due to intermolecular interactions in a poor solvent or at low temperature, whereas they show no activity in the UV-visible region in a good solvent or at high temperatures (5, 9-12). Recent studies (13-16), using optically inactive CPs that become chiral after addition of a chiral guest, show that chirality introduction can also be a result of a main-chain chirality, such as a predominantly one-handed helical structure induced by a acidbase complexation between the CP and the chiral guest.Natural biopolymers such as protein and DNA frequently have helical conformations that contribute to the three-dimensional ordered structure and the specific function of the biopolymer. As a part of the cell signaling pathways and enzymatic reactions, conformational alterations of biomolecules are very important in biological systems. Likewise do the conformational alterations of CPs allow direct connection between the geometry of chains and the resulting electronic structure and optical processes. Hence, it would be of great interest to combine helical biomolecules and optically inactive PTs. Such combinations have been reported (17,18), and an induced chirality in the PTs due to the helical biomolecules was detected. To make a hybrid supermolecule between an optically inactive PT and a biomolecule with a random-coil conformation is ...

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“…However, upon formation of nano-aggregates in poor solvent, significant CD and CPL effects can be observed. 8 It may therefore be expected that circular polarization effects are very sensitive to interchain interactions. Due to the disordered nature of the polymer chains, quantitative analysis of the chiroptical data is very difficult.…”

Section: Introductionmentioning

confidence: 99%

Analysis of the vibronic fine structure in circularly polarized emission spectra from chiral molecular aggregates

Spano

Zhen

Meskers

2004

The Journal of Chemical Physics

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Using a Frenkel-exciton model, the degree of circular polarization of the luminescence (g lum ) from one-dimensional, helical aggregates of chromophoric molecules is investigated theoretically. The coupling between the electronic excitation and a local, intramolecular vibrational mode is taken into account. Analytical expressions for the fluorescence band shape and g lum are presented for the case of strong and weak electronic coupling between the chromophoric units. Results are compared to those from numerical calculations obtained using the three particle approximation. g lum for the 0-0 vibronic band is found to be independent of the relative strength of electronic coupling between chromophores and excitation-vibration coupling. It depends solely on the number of coherently coupled molecules. In contrast, for the higher vibronic transitions ͉g lum ͉ decreases with decreasing strength of the electronic coupling. In the limit of strong electronic coupling, ͉g lum ͉ is almost constant throughout the series of vibronic transitions but for weak coupling ͉g lum ͉ becomes vanishingly small for all vibronic transitions except for the 0-0 transition. The results are interpreted in terms of dynamic localization of the excitation during the zero point vibrational motion in the excited state of the aggregate. It is concluded that circular polarization measurements provide an independent way to determine the coherence size and bandwidth of the lowest exciton state for chiral aggregates.

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On the origin of optical activity in polythiophenes

Cited by 216 publications

References 69 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

Twisting macromolecular chains: Self-assembly of a chiral supermolecule from nonchiral polythiophene polyanions and random-coil synthetic peptides

Analysis of the vibronic fine structure in circularly polarized emission spectra from chiral molecular aggregates

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