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Nature and Energies of Electrons and Holes in a Conjugated Polymer, Polyfluorene
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Abstract
Electrons and holes were injected selectively into poly-2,7-(9,9-dihexylfluorene) (pF) dissolved in a tetrahydrofuran (THF) and a 1,2-dichloroethane (DCE) solution, respectively, using pulse radiolysis. Transient absorption spectra of monoions of both signs revealed two bands attributable to formation of polarons, one in the visible region (pF+• at 580 nm, pF-• at 600 nm) and another in the near-IR region. Additional confirmation for the identification of pF+• and pF-• comes from bimolecular charge-transfer reactions, such as bithiophene-• + pF → pF-• or pF+• + TTA → +TTA+• (TTA = tri-p-tolylamine), in which known radical ions transfer charge to pF or from pF. Difference absorption spectra of pF chemically reduced by sodium in THF provided a ratio of absorbance of anions formed to bleaching of the neutral band at 380 nm. In conjunction with pulse-radiolysis results, the data show that each polaron occupies 4.5 ± 0.5 fluorene units, most probably contiguous units. Extensive reduction of pF by sodium also revealed resistance to formation of bipolarons: excess electrons reside as separate polarons when two or more electrons were injected. Redox equilibria with pyrene and terthiophene by pulse radiolysis established reversible one-electron redox potentials of E0(pF+/0) = +0.66 V and E0(pF0/-) = −2.65 V vs Fc+/0. Together with the excited-state energy, these results predict a singlet exciton binding energy of 0.2 eV for pF in the presence of 0.1 M tetrabutylammonium tetrafluoroborate. This binding energy would increase substantially without an electrolyte.
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This article has been cited by 12 ACS Journal articles (5 most recent appear below).
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40 ns. Almost all of the triplets attached to the chains reached the trap ...
Negative Polaron and Triplet Exciton Diffusion in Organometallic “Molecular Wires”
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Formation and Decay of Fluorobenzene Radical Anions Affected by Their Isomeric Structures and the Number of Fluorine Atoms
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Conjugated “Molecular Wire” for Excitons
Yuki Shibano, Hiroshi Imahori, Paiboon Sreearunothai, Andrew R.Cook and John R. MillerThe Journal of Physical Chemistry Letters2010 1 (9), 1492-1496Conjugated “Molecular Wire” for Excitons
Yuki Shibano, Hiroshi Imahori, Paiboon Sreearunothai, Andrew R.Cook and John R. MillerThe Journal of Physical Chemistry Letters2010 1 (9), 1492-1496We have synthesized new conjugated, rigid rod oligomers of fluorene, Fn(C60)2, n = 4, 8, 12, and 16. These pure compounds have Fn chains up to 140 Å long. The C60 groups covalently attached at both ends serve as traps for excitons created in the Fn ...
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- Published In Issue December 20, 2006
- Received April 13, 2006
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