One-Dimensional Spin Diffusion in Polyacetylene,<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mo>(</mml:mo><mml:mi mathvariant="normal">CH</mml:mi><mml:mo>)</mml:mo></mml:mrow><mml:mrow><mml:mi>x</mml:mi></mml:mrow></mml:msub></mml:mrow></mml:math>

Nechtschein, M.; Devreux, F.; Greene, R. L.; Clarke, Thomas C.; Street, G. B.

doi:10.1103/physrevlett.44.356

Cited by 238 publications

(49 citation statements)

References 17 publications

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“…A dimension-sensitive characteristic of a diffusing carrier is the number of new sites visited in time t, S(t) (14), a quantity basic for the description of processes rate-limited by a simple encounter event by the carrier. Examples include carrier trapping (15), fluorescence quenching (16,17), exciton-exciton annihilation (18) and spin relaxation (19). We present below exact results for S(t) for 2d and 3d anisotropic lattices in an electric field to demonstrate a remarkable interplay between anisotropy a, in hopping rates, electri' field E, and time, inS(t).…”

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confidence: 91%

Field-induced trapping as a probe of dimensionality in molecular crystals

Scher

Alexander

Montroll

1980

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

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The combined effect of an electric field and reduced dimensionality on the hopping motion of a charge carrier in. an anisotropic molecular crystal is determined.'New, exnct -expressions for S(t), the number of distinct sites occupied by a carrier'in time t, are presented for two-dimensional and iree-dimensional anisotropic lattices. The general results are used to model the unusual phenomenon of field-induced charge carrier trapping reported to occur in a quasi-one-dimensional moleculan crystal. An analytic expression for the carrier lifetime r, as a function of the anisotropy in the molecular hopping rates and electric field, is developed and is shown to be in excellent agteement with experimental results. A major conclusion of'the theory is that E~, the electric field characterizing the 9 dependence of Tr, can'be a more direct probe of the'intrinsic anisotropy than is the observed mobility ratio. Considerable interest exists in low-dimension solids such as anisotropic molecular crystals (1), polymeric materials (2, 3), super lattices (4, 5), and inversion layers'(6). Qne and two dimensionality offer opportunities to investigate novel phenomena: consequences of Peierls-Fr6hlich condensation in I-dimensional (1d) (7,8) (20). We show the measured field dependence of the trapping time r(E) to be a direct probe of the hopping rate anisotropy q = wl/w2, wi being the hopping rate along the stack axis and W2 the rate normal to it.Many aspects of triplet-exciton energy transfer and charge-carrier transport of these crystals have been investigated. (22), is 10-2 cm2/V s at room temperature and shows an activated temperature dependence ,rith an activation energy A = 0.11 eV. The electron mobility is interpreted to be intrinsic because the trap concentration needed' for (shallow) trapdominated transport must exceed 1.0%, which is unrealistic for a high-purity zone-refined crystal. An intrinsic mobility exhibiting activated temperature dependence can be a small polaron in the hopping regime (23). The observed mobility ratio A 1/IU2 iS somewhat variable and is typically about 10; this corresponds to an anisotropy in the hopping rates W1/t02 <-102.The details of the hopping motion are not known. It has-been suggested that the donor-acceptor pair, along the stack axis, could act as a single molecular entity. i.e., the excesselectron is partially delocalized on the donor (22). Thus, the electron hopping motion is not primarily from acceptor to nearest acceptor (which is not along the stack axis) as'is the case for the amorphous (trinitrofluorenone-polyvinylcarbazole TNF-PVK) systems (2-4), but rather along the stack axis. If the electron is localized on the pair (A1D1), the hopping transition could be (A1D1) -'(D1A2). A small polaron theory, involving localization on a pair of molecular sites, has been applied to solid rare gases (25,26). ' The'transient photocurrents i (t) for a group of phenanthrene-PMDA crystals is found to be marginally range limited-i.e., ip(t) a exp(-t/r) fort I to, the transit time and the (...

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confidence: 91%

Field-induced trapping as a probe of dimensionality in molecular crystals

Scher

Alexander

Montroll

1980

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

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“…1 7 One estimated D,=5 x 10 -2 cm-2 sec-1 . Using the Overhauser effect and analysis of the proton magnetic resonance T l data, Nechtschein et al 30 estimated the longitudinal diffusion constant of ca. 2 x 10 -2 cnm 2 sec -l.…”

Section: (6)mentioning

confidence: 99%

Electron paramagnetic resonance saturation characteristics of pristine and doped polyacetylenes

Chien¹,

Wnek²,

Karasz³

et al. 1982

Macromolecules

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Electron paramagnetic resonance saturation experiments have been carried out on undoped polyacetylene and on the doped polymer as a function of dopant concentration. The relaxation times of undoped trans-(CH)x show considerable variability from sample to sample, Tr = (2.7 ± 1.7) X 10"5 s and T2 = (7.8 ± 1.0) X 10~8 s, suggesting sensitivity to trace impurities. Exposure to air reduces Tx to 8.1 X 10"6 s and T2 to 6.6 X 10"8 s; this effect is reversible. The use of radioassay techniques with 125I made it possible to prepare and characterize samples of known dopant concentration at the level of parts per million (ppm). There are three distinct regimes which characterize the effect of iodine concentration on the EPR characteristics of trans-(CHly)x. In the region 3 X 10"6 < y < 10"3, T1 decreases with increasing y, while T2 is unaffected. The neutral soliton concentration, [S•], remains constant in this region. Dilute doping results in conversion of S• to a spinless positive soliton S+ and/or direct oxidation of (CH)X to create S+S+ pairs. In the intermediate concentration regime, 10~3 < y < 10"2, both 7\ and T2 decrease with y, and [S•] decreases as y"3•7, suggesting that the dopant is predominantly in the material as I3" with the remainder as I5". When y exceeds 1CT3, there Eire one or more dopant molecules per (CH)X chain and the number of neutral solitons is significantly reduced.In the heavily doped samples, the EPR has a Dysonian line shape until it vanishes for y > 2 X 10~2. The observation of changes in relaxation times even at the dopant level of ppm implies that the dopant ions are randomly distributed throughout the polymer and that the solitons are highly mobile. On the other hand, for cis-(CH)x, doping with iodine from y = 3.3 X 10~5 to 3.9 X 10"4 does not significantly affect 7\ or T2, for pristine cis-(CH)x, Tl = (5.4 ± 0.9) X 10"5 s and T2 = (1.0 ± 0.07) X 10"8 s. Therefore, the solitons in cis-(CH)Z have low diffusivity. Very slowly doped trans-[CH(AsF6);y]x also displays three characteristic regions. In the dilute regime, Tb T2, [S•], and the AZ/pp dependence on Hx are not significantly different from those of pristine trans-(CH)x. Above y > 6 X 10"3, [S-] first decreases with y and then the EPR intensity increases rapidly as the Pauli susceptibility makes its contribution. In the transitional regime, 6 X 10"3 < y < 5 X 10"2, the resonance could not be saturated with the power available, implying Einomalously short rekixation times (Tf), whereas saturation was again possible in the heavily doped metallic limit.

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“…[13][14][15][16] As can be seen in Fig. 6 for several heavily doped polyacetylenes seems to resemble that of the iodine-doped HBC.…”

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confidence: 84%

“…If we remember that the HBC nanotube is a -stacked helical system, it is natural to consider that the spin excitation propagates along the one-dimensional helical chain. To clarify the electronic state in more detail, further investigations including 13 C NMR for the 13 C enriched HBC are now underway.…”

Section: Discussionmentioning

confidence: 99%

Possible One-Dimensional Helical Conductor: Hexa-peri-hexabenzocoronene Nanotube

et al. 2008

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ESR and1 H NMR investigations were performed on iodine-doped HBC nanotubes to understand the low-temperature electronic states and carrier dynamics. Using ESR measurements, we clarified that the charged carriers induced by iodine-doping possess spins, and we found two kinds of spin species with different doping levels. The ESR results indicate the itinerant features down to 170 K. The 1 H T À11 for the heavy-iodine-doped HBC nanotubes follows T 0:5 and exhibits a characteristic frequency dependence. We propose that the spin excitation propagates along the one-dimensional helical chain.

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One-Dimensional Spin Diffusion in Polyacetylene,(CH)x

Cited by 238 publications

References 17 publications

Field-induced trapping as a probe of dimensionality in molecular crystals

Field-induced trapping as a probe of dimensionality in molecular crystals

Electron paramagnetic resonance saturation characteristics of pristine and doped polyacetylenes

Possible One-Dimensional Helical Conductor: Hexa-peri-hexabenzocoronene Nanotube

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