Spectral properties of the longest oligothiophenes in the oxidation states

Nakanishi, H.; Sumi, Naoya; Ueno, Shinpei; Takimiya, Kazuo; Aso, Yoshio; Otsubo, Tetsuo; Komaguchi, Kenji; Shiotani, Masaru; Ohta, Nobuaki

doi:10.1016/s0379-6779(00)01180-2

Cited by 50 publications

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“…23e For oligothiophene radical cations stabilized with substituents at the R-positions of both ends, reversible spectral change supposedly corresponding to the formation of π-dimers has been observed in the electronic and/or ESR spectra at low temperatures. [4][5][6][7][8][9] In the present study, however, variable-temperature electronic-spectral measurements of 1(2T) •+ SbF 6 -and (9); C2-C3, 1.389(11); C3-C4, 1.390(11); C4-S1, 1.761(6); C4-C5, 1.421(9); C5-C6, 1.424(9); C6-C7, 1.389(9); C7-C8, 1.418(9); C8-S2, 1.747(6); S2-C5, 1.751(6); C8-C9, 1.436(9); C9-S3, 1.755(6); C9-C10, 1.389(12); C10-C11, 1.411(11); C11-C12, 1.372-(10); C12-S3, 1.706(6); C1-S1-C4, 90.3(3); S1-C1-C2, 114.9(5); C1-C2-C3, 109.7(7); C2-C3-C4, 115.1(8); C3-C4-S1, 109.9 (5) …”

Section: Chartmentioning

confidence: 99%

“…3 However, in 1992, Miller and co-workers reported the reversible dimerization of a terthiophene radical cation derivative and proposed that the diamagnetic dimer dications formed from the interchain π-stacks of radical cation (i.e., "π-dimers") can be alternatives to bipolarons. 4 Following this influential pro- posal 4 challenging the general perception of polaron/biporalon theory, reversible dimerizations of radical cations have been reported on a wide variety of π-conjugated oligomers, including not only substituted oligothiophenes [5][6][7][8][9] but also other systems such as oligopyrroles, 10 oligo(phenylenevinylene)s, 11 and mixed oligomers composed of benzene, thiophene, or pyrrole units. 12 Whereas these reports assumed π-dimer formation for the interchain interaction of radical cations, Heinze proposed σ-bond formation between two radical cation chains (i.e., σ-dimer formation) on the basis of the results of an electrochemical study on radical cations of diphenylpolyenes, 3,3′,5,5′-tetramethylbithiophene, and oligo(phenylenevinylene)s. 13 This σ-dimer formation was also observed by low-temperature NMR measurement of the radical cation of 5,5′-diphenyl-3,3′,4,4′-tetramethoxybipyrrole in solution, although in the solid state the radical cation salts showed the π-stacked structure without any σ-bond formation.…”

Section: Introductionmentioning

confidence: 99%

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Crystal Structures and Spectroscopic Characterization of Radical Cations and Dications of Oligothiophenes Stabilized by Annelation with Bicyclo[2.2.2]octene Units: Sterically Segregated Cationic Oligothiophenes

et al. 2004

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The remarkably stable SbF(6)(-) salts of the radical cations of bithiophene 1(2T) and terthiophene 1(3T), completely surrounded by bicyclo[2.2.2]octene (BCO) units, were obtained by one-electron oxidation of the neutral precursors with NO(+)SbF(6)(-), and their solid-state structures were determined by X-ray crystallography. In these radical cations, the presence of quinoidal character was apparent, as shown by the increased planarity and by comparison of the bond lengths with those of the neutral precursors. The shortest intermolecular pi-pi distances in the crystal structure of 1(2T)(*)(+)SbF(6)(-) (distance between two sp(2) carbon atoms, 4.89 A) and 1(3T)(*)(+)SbF(6)(-) (distance between an sp(2) carbon and a sulfur atom, 3.58 A) were found to be longer than the sums of the van der Waals radii of the corresponding atoms. In accord with this, no apparent change was observed in ESR and UV-vis-NIR spectra of solutions of 1(2T)(*)(+) and 1(3T)(*)(+) upon lowering the temperature, indicating that the pi- (or sigma-) dimer formation is inhibited in solution as well as in the solid state. The dications 1(2T)(2+) and 1(3T)(2+) were generated with the stronger oxidant SbF(5) in CH(2)Cl(2) at -40 degrees C and characterized by NMR spectroscopy. In the (1)H NMR spectra, two conformers were observed for each dication of both 1(2T)(2+) (transoid (t) and cisoid (c)) and 1(3T)(2+) (t,t and c,t) at room temperature due to the high rotational barrier around the inter-ring bond(s) between thiophene rings, which was caused by the enhanced double bond character of these bonds following two-electron oxidation. This is supported by DFT calculations (B3LYP/6-31G(d)), which predicted the rotational barriers in the dications of unsubstituted bithiophene and terthiophene to be 27.6 and 22.9 kcal mol(-)(1), respectively. In the case of quaterthiophene and sexithiophene surrounded by BCO frameworks 1(4T) and 1(6T), oxidation with even one molar equivalent of NO(+)SbF(6)(-) afforded the dication salts 1(4T)(2+)2SbF(6)(-) and 1(6T)(2+)2SbF(6)(-), which were isolated as stable single crystals and allowed the X-ray crystallography. In their crystal structures, the cationic pi-systems became planar again due to the great contribution of quinoidal resonance structures, and the pi-systems, which were arrayed in a parallel geometry, were also segregated by the steric effect of BCO units. The degree and tendency of changes in the bond lengths of thiophene rings of 1(4T)(2+) and 1(6T)(2+) as compared with neutral precursors were similar to those of 1(2T)(*)(+)SbF(6)(-) and 1(3T)(*)(+)SbF(6)(-), respectively, implying that the contribution of quinoidal character is modulated by the amount of positive charge per thiophene unit.

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Section: Chartmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Crystal Structures and Spectroscopic Characterization of Radical Cations and Dications of Oligothiophenes Stabilized by Annelation with Bicyclo[2.2.2]octene Units: Sterically Segregated Cationic Oligothiophenes

et al. 2004

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“…[19][20][21]24 An alternative rationalization for the small ESR signals in doped PT was suggested when experiments revealed that duodecithiophene and longer OTs give rise to UV spectra that are consistent with spinless interacting polaron pairs located on the same chain. 32,34,35 Theoretical investigations of excited states for bi-and terthiophene cations have been carried out at the complete active space self-consistent field CASSCF 36 and CASPT2 37 levels of theory. The calculations agree with the experimental solution data and predict two excitations for radical cations.…”

Section: Introductionmentioning

confidence: 99%

Theoretical Investigation of Excited States of Oligothiophenes and of Their Monocations

Salzner

2007

J. Chem. Theory Comput.

123

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Excitation energies of neutral thiophene oligomers with chain lengths of up to 25 rings and charged thiophene oligomers with chain lengths of up to 20 rings were calculated with time-dependent Hartree-Fock and time-dependent density functional theory (TDDFT). As recently for polyene cations, very good agreement is found between TDDFT and high-level ab initio calculations and with experimental results wherever data are available. For short thiophene oligomer cations, two sub-band transitions are predicted; for long chains, a third transition develops. Defects are found to be delocalized in bare cations; the inclusion of counterions induces localization. Despite the strong influence of counterions on the geometry, the influence of counterions on the spectra is small for the first two sub-band peaks. Since counterions are directly involved in the electron transitions contributing to the third sub-band peak of longer oligomers, the inclusion of counterions lowers the energy of this absorption peak. The agreement between theoretical spectra based on delocalized geometries and experimental spectra shows that defect localization (electron phonon coupling) is not the underlying cause of the two sub-band transitions. Investigation of the electronic configurations that contribute to the excited states does not confirm the nature of the transitions predicted with the polaron model.

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“…Electron-hole symmetry was confirmed experimentally for didodecylsexithiophene, which forms stable mono-and dications and anions. 19 In contrast to the predictions based on the polaron-bipolaron model (Scheme 1), [13][14][15][16][17] experimental doping studies of oligothiophenes (OTs) in solution [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] showed that monocations (polarons) are associated with two sub-band transitions, while dications (bipolarons) give rise to only one sub-band feature. This was confirmed with theoretical investigations at various semiempirical [36][37][38][39] and ab initio levels, 34,40 and with density functional theory (DFT).…”

Section: Introductionmentioning

confidence: 99%

Theoretical Investigation of Excited States of Oligothiophene Anions

Alkan

Salzner

2008

J. Phys. Chem. A

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Electron-hole symmetry upon p-and n-doping of conducting organic polymers is rationalized with Hückel theory by the presence of symmetrically located intragap states. Since density functional theory (DFT) predicts very different geometries and energy level diagrams for conjugated π-systems than semiempirical methods, it is an interesting question whether DFT confirms the existence of electron-hole symmetry predicted at the Hückel level. To answer this question, geometries of oligothiophene anions with 5-19 rings were optimized and their UV/vis spectra were calculated with time-dependent DFT. Although DFT does not produce symmetrically placed sub-band energy levels, spectra of cations and anions are almost identical. The similarity in transition energies and oscillator strengths of anions and cations can be explained by the fact that the single sub-band energy level of cations lies above the valence band by the same amount of energy as the single sub-band level of anions lies below the conduction band. This and the resemblance of the energy level spacings in valence bands of cations to those in conduction bands of anions give rise to peaks with equal energies and oscillator strengths.

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Spectral properties of the longest oligothiophenes in the oxidation states

Cited by 50 publications

References 0 publications

Crystal Structures and Spectroscopic Characterization of Radical Cations and Dications of Oligothiophenes Stabilized by Annelation with Bicyclo[2.2.2]octene Units: Sterically Segregated Cationic Oligothiophenes

Crystal Structures and Spectroscopic Characterization of Radical Cations and Dications of Oligothiophenes Stabilized by Annelation with Bicyclo[2.2.2]octene Units: Sterically Segregated Cationic Oligothiophenes

Theoretical Investigation of Excited States of Oligothiophenes and of Their Monocations

Theoretical Investigation of Excited States of Oligothiophene Anions

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