Size dependence of triplet and singlet states of α-oligothiophenes

Rentsch, S.; Yang, Jiping; Paa, W.; Birckner, Eckhard; Schiedt, J.; Weinkauf, R.

doi:10.1039/a808617f

Cited by 92 publications

(183 citation statements)

References 21 publications

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“…The situation is different for 2,2 0 -bithiophene (hereafter referred to as bithiophene or 2T), mostly due to the relatively large size of the molecule. It is, however, well documented [21][22][23] that the adiabatic energy of the lowest, dipole-allowed excitation is located at 3.83-3.88 eV. Room temperature gas-phase [23] and solution spectra [24] revealed an intensive band with oscillator strength f = 0.29 located just above 4 eV and a weaker one with f = 0.13, at about 5 eV.…”

Section: Introductionmentioning

confidence: 99%

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The elusive excited states of bithiophene: a CASPT2 detective story

Andrzejak

Witek

2011

Theor Chem Acc

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Section: Introductionmentioning

confidence: 99%

“…The supersonic-jet [21] and the photodetachment photoelectron spectra [22] show that the gas-phase adiabatic excitation energy for the lowest dipole-allowed state (X 1 A g ? 1 1 B u ) can be quite firmly set at 3.86-3.88 eV.…”

Section: Experimental Evidencementioning

confidence: 99%

The elusive excited states of bithiophene: a CASPT2 detective story

Andrzejak

Witek

2011

Theor Chem Acc

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“…In the steadystate absorption studies, however, only one-photon allowed transitions from the ground state are observed while the other excited states are not monitored. Photodetachment photoelectron spectroscopy (PD-PES) 14,15 and high-resolution electron energy loss spectroscopy (HREELS) 16,17 have been performed for estimating the energies of the low-lying triplet and singlet states in solid films, respectively. The effects of solvents on the effective conjugation length in the low-lying excited states, however, are not well understood, because these methods are not easily applicable to solutions.…”

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confidence: 99%

Femtosecond Time-resolved Near-infrared Spectroscopy of Oligothiophenes and Polythiophene: Energy Location and Effective Conjugation Length of Their Low-lying Excited States

2015

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The energies of low-lying singlet excited states of oligothiophenes, xT's (x = 3 to 8), and polythiophene are determined using femtosecond time-resolved near-infrared spectroscopy. The energies are linearly correlated with the reciprocal number of the thiophene rings for the oligomers 3T to 7T. The linear relation is not observed for 8T, indicating that the effective conjugation is formed over no more than seven rings in the excited states. Transient absorption spectra of polythiophene show that its thiophene chains are composed of planar segments with five or six thiophene rings.Organic polymers with large conjugate systems are a group of fundamental compounds for investigating the properties of onedimensional π-conjugate structure, such as large conductivity 1 and strong photoluminescence associated with photoexcitation.2 The molecular structure of the polymer significantly influences the electronic structure and the dynamics of excitations photogenerated in the polymer. In solution, the effective conjugation length can be shorter than the entire length of the polymer because solutesolvent interactions will create a number of kinks in the conjugate structure.Polythiophene is widely used as a model compound of the one-dimensional π-conjugate polymer, for evaluating the effective conjugation length in solid films and in solutions as well as for understanding the excitation dynamics. The excitation dynamics of oligothiophenes has been observed by time-resolved absorption 36 and emission spectroscopy. 7,8 The electronic or vibrational transition energies have been evaluated by steady-state absorption 911 and Raman spectroscopy 12,13 for neutral or charged oligothiophenes in the ground state, which are regarded as a partial structure of a polymer segmented with kinks. In the steadystate absorption studies, however, only one-photon allowed transitions from the ground state are observed while the other excited states are not monitored. Photodetachment photoelectron spectroscopy (PD-PES) 14,15 and high-resolution electron energy loss spectroscopy (HREELS) 16,17 have been performed for estimating the energies of the low-lying triplet and singlet states in solid films, respectively. The effects of solvents on the effective conjugation length in the low-lying excited states, however, are not well understood, because these methods are not easily applicable to solutions.New photophysics and photochemistry are expected when a polymer is photoexcited to an excited singlet state located higher than the lowest one. It is unclear if the effective conjugation length is preserved in the highly excited singlet states compared with the ground or lowest excited singlet state. In this study, we observed the highly excited singlet states of α-oligothiophenes and α-polythiophene by femtosecond time-resolved near-infrared absorption spectroscopy. The results for α-oligothiophenes composed of 3 to 7 thiophene rings show a systematic downshift of the absorption peak wavelength in the transient near-infrared absorption spectra at 11 ps, w...

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“…Oligothiophenes with 2, 3, and 4 monomer units have decreasing transition energies of triplet and singlet states with increasing chain length [87]. Fichou et al have reported low temperature optical absorption of polycrystalline thin films of 4T, 6T, and 8T with a fundamental π-π * absorption band ranging from 300 nm -500 nm.…”

Section: Overviewmentioning

confidence: 99%

Two-photon Photoemission of Organic Semiconductor Molecules on Ag(111)

Yang

2008

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Angle-and time-resolved two-photon photoemission (2PPE) was used to study systems of organic semiconductors on Ag(111). The 2PPE studies focused on electronic behavior specific to interfaces and ultrathin films. Electron time dynamics and band dispersions were characterized for ultrathin films of a prototypical n-type planar aromatic hydrocarbon, PTCDA, and representatives from a family of p-type oligothiophenes.In PTCDA, electronic behavior was correlated with film morphology and growth modes.Within a few monolayers of the interface, image potential states and a LUMO+1 state were detected. The degree to which the LUMO+1 state exhibited a band mass less than a free electron mass depended on the crystallinity of the layer. Similarly, image potential states were measured to have free electron-like effective masses on ordered surfaces, and the effective masses increased with disorder within the thin film. Electron lifetimes were correlated with film growth modes, such that the lifetimes of electrons excited into systems created by layer-by-layer, amorphous film growth increased by orders of magnitude by only a few monolayers from the surface. Conversely, the decay dynamics of electrons in Stranski-Krastanov systems were limited by interaction with the exposed wetting layer, which limited the barrier to decay back into the metal.Oligothiophenes including monothiophene, quaterthiophene, and sexithiophene were deposited on Ag(111), and their electronic energy levels and effective masses were studied as a function of oligothiophene length. The energy gap between HOMO and LUMO decreased with increasing chain length, but effective mass was found to depend on domains 2 from high-or low-temperature growth conditions rather than chain length. In addition, the geometry of the molecule on the surface, e.g., tilted or planar, substantially affected the electronic structure.

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Size dependence of triplet and singlet states of α-oligothiophenes

Cited by 92 publications

References 21 publications

The elusive excited states of bithiophene: a CASPT2 detective story

The elusive excited states of bithiophene: a CASPT2 detective story

Femtosecond Time-resolved Near-infrared Spectroscopy of Oligothiophenes and Polythiophene: Energy Location and Effective Conjugation Length of Their Low-lying Excited States

Two-photon Photoemission of Organic Semiconductor Molecules on Ag(111)

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