In situ EPR/UV–VIS spectroelectrochemistry of polypyrrole redox cycling

Rapta, Peter; Neudeck, Andreas; Petr, Andreas; Dunsch, Lothar

doi:10.1039/a806423g

Cited by 69 publications

(57 citation statements)

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“…14,98 At higher doping levels both bands shift to higher energy and two absorptions occur at 1.0 and 2.7 eV. 12 In contrast, Street et al 52 reported an absorption energy of 1.3 eV after oxidation with oxygen, Zotti et al 18 and Rapta et al 25 observed a band at 1.38 eV, and Fink et al 13 found two peaks at 1.5-2.0 eV and at 3.0 eV with electron energy loss spectroscopy at higher doping levels. Although there are significant differences in reported data and in the interpretation of experimental results, on combining polymer and oligomer data the following picture emerges: (1) since the absorption maximum of polypyrrole is close to that or slightly below that of 7P, conjugation length in PPy is likely in the range of seven to nine rings (as found also with Raman spectroscopy 99 ); (2) monocations and polarons give rise to two sub-band peaks at about 0.7-0.8 and 2.1-2.3 eV, while dications or bipolarons have a characteristic absorption in the range 1.0-1.4 eV.…”

Section: Discussionmentioning

confidence: 99%

“…12,13,[16][17][18] The sub-band transitions of doped COPs were rationalized originally in terms of bipolaron formation since there is no correlation between ESR signals and conductivity. 9,[19][20][21][22] Preference for bipolarons has been questioned by some experimentalists from the start, 17,18,[23][24][25][26] but others rationalized their observations in terms of bipolarons. 13,16,22 Especially after the doping behavior of monodisperse polyenes [27][28][29] and oligothiophenes (OTs) [30][31][32][33][34][35][36][37][38][39][40][41] was investigated in solution, the bipolaron model was challenged.…”

Section: Introductionmentioning

confidence: 99%

“…[49][50][51] In the oligomer studies the issue of bipolaron formation was not addressed and the interpretation of polymer results remains controversial. 8,12,13,16,17,20,22,23,25,[52][53][54][55] Electronic structures of PPy and OPs have been investigated theoretically before; 20,[56][57][58][59][60][61][62][63][64][65][66][67][68][69][70] however, we are not aware of calculations of absorption spectra during the doping process of pyrrole oligomers or polymers. We have recently calculated such spectra for polyenes 71 and OTs.…”

Section: Introductionmentioning

confidence: 99%

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Theoretical Modeling of the Doping Process in Polypyrrole by Calculating UV/Vis Absorption Spectra of Neutral and Charged Oligomers

Okur

Salzner

2008

J. Phys. Chem. A

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Changes in absorption spectra during doping of oligopyrroles were investigated with time-dependent density functional theory on optimized structures of neutral, singly, and doubly charged pyrrole oligomers with up to 24 rings. In the absence of counterions, defects are delocalized. Counterions induce localization. For dications two polarons on the same chain are preferred over a bipolaron. Intragap absorptions arise in charged species, no matter whether defects are localized or delocalized. Cations and dications give rise to two sub-band transitions. The cation peaks have lower energies than those of dications. The first excitations of cations have lower oscillator strengths than the second; for dications the second peak is weaker than the first. For very long oligomers, the second sub-band absorption vanishes and a third one appears at higher energy. The behavior of pyrrole oligomers is analogous to that of thiophene oligomers. Theoretical UV spectra for cations and dications of short oligomers (six to eight rings) match experimental spectra of polypyrrole at low and at high doping levels, respectively. The error in the theoretical calculations is about 0.4 eV, slightly larger than for thiophene oligomers at the same level of theory.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Theoretical Modeling of the Doping Process in Polypyrrole by Calculating UV/Vis Absorption Spectra of Neutral and Charged Oligomers

Okur

Salzner

2008

J. Phys. Chem. A

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“…A detailed description of the spectroelectrochemical flat cell together with the electrode system and its preparation can be found elsewhere. [25,26] Measurements at 360 K were carried out in a small flat spectroelectrochemical cell for temperature-controlled experiments. [27] The tightly closed cells were transferred from the glove box into the EPR cavity (ER4104OR or ER4103TM, both Bruker, Germany) where the EPR spectra were acquired.…”

Section: Methodsmentioning

confidence: 99%

Redox Properties of Mixed Lutetium/Yttrium Nitride Clusterfullerenes: Endohedral Lu_xY_3−xN@C₈₀(I) (x=0–3) Compounds

2009

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The redox behavior of mixed lutetium/yttrium nitride clusterfullerenes of the series Lu(x)Y(3-x)N@C(80)(I(h), x = 0-3) is studied for the first time by means of cyclic voltammetry, fast-scan cyclic voltammetry, square-wave voltammetry, and electron paramagnetic resonance (EPR) spectroelectrochemistry. A reversible single-electron-transfer process, which does not result in an EPR signal, is detected during the anodic oxidation sweep of cyclic voltammetry experiments performed at different temperatures (296 and 360 K). The cathodic reduction sweep reveals a rather complex response for all the four clusterfullerenes--with up to three irreversible reduction steps. By correlating the results of fast-scan and square-wave voltammetry and combining them with simulations of the voltammograms, we are able to propose a reduction mechanism for the Lu(x)Y(3-x)N@C(80)(I) (x = 0-3) fullerenes.

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“…Similar experiments with this cell construction were successfully applied to the spectroelectrochemistry of pyrrole hexamer by using a gold micromesh electrode. [17] The gold LIGA electrodes used in this study ensure stable handling during the measurements due to their mechanical stability. The larger active and welldefined metal electrode surface of the LIGA structure results in a better electrochemical response compared to commercially available gold micromeshes, which is advantageous for detailed mechanistic studies.…”

Section: Resultsmentioning

confidence: 99%

In Situ Spectroelectrochemical Studies on Ladder‐Type Oligomers in Solution and the Solid State

Rapta

Schulte

Schlüter

et al. 2006

Chemistry A European J

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A series of thermally stable fluoranthenopyracylene oligomers with extended pi conjugation were studied by in situ ESR-UV/Vis/NIR spectroelectrochemistry with respect to their application in devices such as organic light-emitting diodes and field-effect transistors. The oligomers are both soluble in o-dichlorobenzene and form thin films by evaporation in the temperature range of 300-500 degrees C in vacuum. Their electrochemical behavior was studied in reduction (n doping) and oxidation (p doping) under standard voltammetric and thin-layer conditions. The HOMO and LUMO energies and the band gaps of all compounds under study were estimated from both electrochemical and UV/Vis/NIR spectroscopic data. The fluorene-type oligomers A(2)-A(6) and B(2) bearing flexible alkyl chains exhibit both reversible multistep reductions and oxidations. The spectroelectrochemistry indicates substantial differences in delocalization of the positive and negative charges in these ladder-type oligomers. The formation of doubly charged sigma dimers was observed for the first time for both the radical anion and radical cation of the same molecule (B(1)). The redox behavior of the oligomers was studied in the solid state and in solution.

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In situ EPR/UV–VIS spectroelectrochemistry of polypyrrole redox cycling

Cited by 69 publications

References 2 publications

Theoretical Modeling of the Doping Process in Polypyrrole by Calculating UV/Vis Absorption Spectra of Neutral and Charged Oligomers

Theoretical Modeling of the Doping Process in Polypyrrole by Calculating UV/Vis Absorption Spectra of Neutral and Charged Oligomers

Redox Properties of Mixed Lutetium/Yttrium Nitride Clusterfullerenes: Endohedral Lu_xY_3−xN@C₈₀(I) (x=0–3) Compounds

In Situ Spectroelectrochemical Studies on Ladder‐Type Oligomers in Solution and the Solid State

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In situ EPR/UV–VIS spectroelectrochemistry of polypyrrole redox cycling

Cited by 69 publications

References 2 publications

Theoretical Modeling of the Doping Process in Polypyrrole by Calculating UV/Vis Absorption Spectra of Neutral and Charged Oligomers

Theoretical Modeling of the Doping Process in Polypyrrole by Calculating UV/Vis Absorption Spectra of Neutral and Charged Oligomers

Redox Properties of Mixed Lutetium/Yttrium Nitride Clusterfullerenes: Endohedral LuxY3−xN@C80(I) (x=0–3) Compounds

In Situ Spectroelectrochemical Studies on Ladder‐Type Oligomers in Solution and the Solid State

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Redox Properties of Mixed Lutetium/Yttrium Nitride Clusterfullerenes: Endohedral Lu_xY_3−xN@C₈₀(I) (x=0–3) Compounds