Polaron lattice in highly conducting polyaniline: Theoretical and optical studies

Stafström, Sven; Brédas, Jean Luc; Epstein, Arthur J.; Woo, Hyung-Suk; Tanner, D. B.; Huang, Wu‐Song; MacDiarmid, Alan G.

doi:10.1103/physrevlett.59.1464

Cited by 880 publications

(465 citation statements)

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“…Therefore, the transient absorption on sub-picoseconds to tens of picoseconds time scales observed from 850 to 1025 nm, as shown in Figures 2 and 3, is associated with a long-lived photoexcited polaron state. Furthermore, judging from the width of the polaron band that was estimated to be ∼1.1 eV, 43 this transient absorption is an intraband absorption in the polaron band (see Figure 10).…”

Section: Discussionmentioning

confidence: 97%

“…Case 1 is reasonable in that the delayed absorption is observed on the blue side (650-700 nm), but it requires that the polaron band have a large bandwidth of at least 1.8 eV (650 nm), which is more than 50% larger than the predicted value of 1.1 eV from the calculation by Bredas. 43,45 Case 2 is possible in terms of the energy difference between the lower polaron band and upper polaron/conduction band. From the absorption spectrum of PD-PANI, 74 the gap between the valence and conduction band is predicted to be ∼3.4 eV (360 nm).…”

Section: Discussionmentioning

confidence: 99%

“…For example, the bandwidth of the polaron band in PD-PANI was theoretically predicted to be ∼1.1 eV. 43 Second, the rapid changes in the extinctions of the transitions associated with cooling in the first excited state were considered.…”

Section: Kinetic Modeling Of Relaxationmentioning

confidence: 99%

“…The proposed band structure of conductive PANI, based on the band structure calculations for the polaron lattice of PANI, 43,45 is schematically illustrated in Figure 10 lower polaron band is half-filled and has a significant bandwidth. The details of the band structure, for example, comparison of electronic structures of PD-and SD-PANI, will be further discussed in the next section.…”

Section: Kinetic Modeling Of Relaxationmentioning

confidence: 99%

“…This leaves only one broad polaron band (i.e., the lower polaron band) in the bandgap with the Fermi level at the middle of this half-filled band. The calculations predict [43][44][45] two transitions to the polaron band from the valence band, at 1.8 and 2.6 eV, with intraband absorption in the IR region. These findings agree with the experimental linear absorption spectrum of PD-PANI.…”

Section: Introductionmentioning

confidence: 99%

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Ultrafast Dynamics of Polarons in Conductive Polyaniline: Comparison of Primary and Secondary Doped Forms

2008

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Time-and wavelength-resolved pump-probe measurements are performed on the conductive, primary and secondary doped, forms of polyaniline in solution to investigate the relaxation dynamics of photoexcited polarons. Contrasting dynamics observed in the two forms allow investigation of electronic (and structural) relaxation of this material. Pump pulse at 800 nm photoexcites an electron from the valence to polaron band, and subsequent relaxation dynamics are probed by a white light continuum pulse. Three distinct features are observed in the primary doped sample: (1) absorption near time zero in the 900-1025 nm probe wavelength region; (2) delayed absorption from 850 to 1025 nm; (3) pronounced oscillations with frequencies of 165 and 210 cm -1 . The first two features are associated with intraband absorptions to higher-lying states in the polaron band from the initial excited and conformationally changed intermediate states. The oscillations reflect torsional motions associated with photoexcitation and relaxation. In the secondary doped material, only bleaching and stimulated emission are observed throughout the whole spectral region; neither transient absorption signals nor oscillatory dynamics are observed. Kinetic modeling is performed to establish the mechanism of relaxation. We propose that the excited polaron relaxes nonradiatively to the ground state through an intermediate state(s) with a twisted geometry. Our measurements and analysis allow us to describe the structure of the polaron bands for primary and secondary doped polyaniline; they are in the small and large polaron limits, respectively, and are consistent with a bandgap for the primary doped form and without a bandgap (i.e., metallic) for the secondary doped material.

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Section: Discussionmentioning

confidence: 97%

Section: Discussionmentioning

confidence: 99%

Section: Kinetic Modeling Of Relaxationmentioning

confidence: 99%

Section: Kinetic Modeling Of Relaxationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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