Polarization dependence of the ultrafast photoluminescence of oriented poly(<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>p</mml:mi></mml:math>-phenylenevinylene)

Hayes, Gary; Samuel, Ifor D. W.; Phillips, R. T.

doi:10.1103/physrevb.56.3838

Cited by 44 publications

(44 citation statements)

References 29 publications

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“…Depolarization of spontaneous (PL) and stimulated emission (TA signal in this paper) in film can occur due to incoherent hopping along and between polymer chains [12][13][14][15][16][17]. Partially conjugated MEH-PPV (with 33% of chemical conjugation breaks per number of repeat units) showed the initial depolarization of emission with a time constant of ~1 ps in solution, which can be explained by incoherent exciton hopping [10].…”

Section: Resultsmentioning

confidence: 91%

Exciton self‐trapping in MEH‐PPV films studied by ultrafast emission depolarization

Ruseckas¹,

Samuel

2006

Phys. Status Solidi (c)

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Depolarization of the transient absorption with a time constant of <120 fs is observed in poly[2-(2'-ethylhexyloxy)-5-methoxy-1,4-phenylenevinylene] (MEH-PPV) film. It is too fast to be explained by incoherent hopping. We attribute it to dynamic localization (self-trapping) of the initially delocalized excitons driven by structural relaxation of excited segments. Implications for charge carrier photogeneration are briefly discussed.1 Introduction Conjugated polymers with a strong electronic coupling along their backbone represent interesting model quasi-1D systems and are promising materials for light emitting and photovoltaic applications. Formation and dynamics of emitting electronic states (excitons) is therefore of particular interest. The extent of exciton delocalization along the conjugated chain, which is determined by electronic coupling, conformational defects and electron-phonon interaction, is still unresolved issue in these materials. Dynamic localization of the exciton (self-trapping) on six to ten repeat units has been theoretically predicted for poly(phenylene-vinylene) (PPV) as an outcome of structural relaxation [1][2][3]. Such a relaxation is likely to be the cause of the rapid decay of the three-pulse stimulated echo peak shift within 50 fs observed in a PPV derivative poly[2-(2'-ethylhexyloxy)-5-methoxy-1,4-phenylenevinylene] (MEH-PPV) in solution [4], but no information on exciton localization length can be extracted from these data. The relaxation energy in the polymer was in fact very similar to that in a PPV pentamer, where delocalization of the primarily exciton is limited by pentamer length. Ultrafast vibrational coherence gives an indication of structural relaxation within 100 fs in another conjugated polymer polydiacetylene [5]. Some information on exciton size (maximal distance between electron and hole) is obtained from polarizabilities, which can be measured by electroabsorption in the Franck-Condon region (before structural relaxation) [6,7] and by GHz and THz conductivity for the relaxed excitons [8,9]. Polarizability increases with the length of conjugated oligomers [7,8], and thus, with the size of exciton. Electroabsorption experiments on MEH-PPV films showed that polarizability along the conjugated backbone of the non-relaxed excitons decreases with an increase of the photon energy, which generates the exciton, and ranges between 3000 and 12000 Å 3 for the photon energies of 2.2 and 2.1 eV [6]. The THz conductivity of relaxed excitons measured after excitation with 3.1 eV photons gives polarizability of ~2300 Å

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Section: Resultsmentioning

confidence: 91%

Exciton self‐trapping in MEH‐PPV films studied by ultrafast emission depolarization

Ruseckas¹,

Samuel

2006

Phys. Status Solidi (c)

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“…Ultrafast luminescence measurements were performed using up-conversion spectroscopy. 22 The 850 nm output (FWHM = 100 fs) from a Ti:Sapphire oscillator was frequency doubled with a BBO crystal to generate the excitation pulse, while residual 850 nm light was used as the gating pulse after reflection with an optical delay line. Fluorescence was collected and focused onto a sumfrequency generation (SFG) BBO crystal along with the 850 nm gating pulse.…”

Section: Methodsmentioning

confidence: 99%

Ultrafast Electronic Energy Transfer Beyond the Weak Coupling Limit in a Proximal but Orthogonal Molecular Dyad

et al. 2015

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Electronic energy transfer (EET) from a donor to an acceptor is an important mechanism that controls the light harvesting efficiency in a wide variety of systems, including artificial and natural photosynthesis and contemporary photovoltaic technologies. The detailed mechanism of EET at short distances or large angles between the donor and acceptor is poorly understood. Here the influence of the orientation between the donor and acceptor on EET is explored using a molecule with two nearly perpendicular chromophores. Very fast EET with a time constant of 120 fs is observed, which is at least forty times faster than the time predicted by Coulombic coupling calculations. Depolarization of the emission signal indicates that the transition dipole rotates through ca. 64 0 , indicating the near orthogonal nature of the EET event. The rate of EET is found to be similar to structural relaxation rates in the photo-excited oligothiophene donor alone, which suggests that this initial relaxation brings the dyad to a conical intersection where the excitation jumps to the acceptor.

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“…This last effect suggests that the nanofluidic filling leads to an enhancement of the molecular order and alignment in the nanochannels. In fact, since conjugated polymers emit preferentially along transition dipole moments, collinear to radiative conjugated segments, and along molecular chains (deviations within about 208 have been reported), [16] such flow-induced orientation of molecules within mutually aligned organic nanofibers can be exploited to obtain devices with macroscopic optical anisotropy. To investigate this issue, we analyzed the polarization state of the nanofiber emission.…”

Section: à7mentioning

confidence: 98%

Organic Light‐Emitting Nanofibers by Solvent‐Resistant Nanofluidics

et al. 2008

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Solvent‐resistant nanofluidics is demonstrated as sub‐100‐nm technology for fabricating organic light‐emitting fibers, with superior control over diameter and spatial arrangement. Nanofluidics is carried out with optimal resistance to organic solvents commonly employed to dissolve conjugated polymers. The optically active nanofibers, with diameters around 60 nm, are found to exhibit photoluminescence emission polarized along their axis.

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Polarization dependence of the ultrafast photoluminescence of oriented poly(p-phenylenevinylene)

Cited by 44 publications

References 29 publications

Exciton self‐trapping in MEH‐PPV films studied by ultrafast emission depolarization

Exciton self‐trapping in MEH‐PPV films studied by ultrafast emission depolarization

Ultrafast Electronic Energy Transfer Beyond the Weak Coupling Limit in a Proximal but Orthogonal Molecular Dyad

Organic Light‐Emitting Nanofibers by Solvent‐Resistant Nanofluidics

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