Femtosecond Time-Resolved Spectroscopic Studies on Thiophene Oligomers

Lap, D. V.; Grebner, D.; Rentsch, S.

doi:10.1021/jp961670n

Cited by 56 publications

(57 citation statements)

References 31 publications

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“…The UVvisible region is dominated by a strong peak, polarized along the long (x) axis of the molecule, 51 and governed by the π-π * transition between the highest-occupied molecular orbital, HOMO (H), and the lowest-unoccupied molecular orbital, LUMO (L). Our finding, indicating the lowest excitation energy of 2T at 4.05 -4.09 eV (see Table I), is in agreement with experiments, [52][53][54][55][56] and with quantum-chemistry results, 57,58 which evaluate the peak between 4.05 and 4.11 eV. As the size of the oligomer increases, discrepancies between the G 0 W 0 +BSE and ALDA spectra emerge in both the energy of the first peak and the overall spectral shape.…”

Section: A Molecules Of Increasing Lengthsupporting

confidence: 92%

Optical spectra from molecules to crystals: Insight from many-body perturbation theory

Cocchi

Draxl

2015

Phys. Rev. B

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Time-dependent density-functional theory (TDDFT) often successfully reproduces excitation energies of finite systems, already in the adiabatic local-density approximation (ALDA). Here we show for prototypical molecular materials, i.e., oligothiophenes, that ALDA largely fails and explain why this is so. By comparing TDDFT with an in-depth analysis based on many-body perturbation theory, we demonstrate that correlation effects crucially impact energies and character of the optical excitations not only for molecules of increasing length and in crystalline environment, but even for isolated small molecules. We argue that only high-level methodologies, which explicitly include correlation effects, can reproduce optical spectra of molecular materials with equal accuracy from gas phase to crystal structures.

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Section: A Molecules Of Increasing Lengthsupporting

confidence: 92%

Optical spectra from molecules to crystals: Insight from many-body perturbation theory

Cocchi

Draxl

2015

Phys. Rev. B

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“…The energy of the S n ¤¤¤ state shares the same line that represents the relation between the x ¹1 value and the energy of an excited state observed in the visible region for 3T to 6T. 6 A linear relation is found in the HREELS spectra for 4T to 8T in thin solid films as well. 17 The results of HREELS also indicate the linear relation between the energy and the x ¹1 value obtained in this study, although the optical transitions follow different selection rules from electron spectroscopy.…”

mentioning

confidence: 60%

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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Section: Excited State Dynamics Of Bithiophenementioning

confidence: 99%

“…22 The lowest excited singlet state of bithiophene was shown to decay in a relatively long time (lifetime 51 ps) 73 and the population transfer was attributed to an intersystem crossing with an efficiency of 0.99. 17,73 Note that the experiments 17,73 were performed in dioxane and benzene. While several quantum chemical studies dealt with singlet and triplet excited states of bithiophene, 17,36,37,[74][75][76] the most recent one of Weinkauf et al 38 (including oligothiophenes of chain lengths 2 to 6) attributes efficient intersystem crossing to a transition from the S 1 state to the lower triplet state T 2 , which subsequently transfers its population to the T 1 state.…”

Section: Excited State Dynamics Of Bithiophenementioning

confidence: 99%

Excited state dynamics of thiophene and bithiophene: new insights into theoretically challenging systems

Prlj

Curchod

Corminbœuf

2015

Phys. Chem. Chem. Phys.

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The computational elucidation and proper description of the ultrafast deactivation mechanisms of simple organic electronic units, such as thiophene and its oligomers, is as challenging as it is contentious. A comprehensive excited state dynamics analysis of these systems utilizing reliable electronic structure approaches is currently lacking, with earlier pictures of the photochemistry of these systems being conceived based upon high-level static computations or lower level dynamic trajectories. Here a detailed surface hopping molecular dynamics of thiophene and bithiophene using the algebraic diagrammatic construction to second order (ADC(2)) method is presented. Our findings illustrate that ring puckering plays an important role in thiophene photochemistry and that the photostability increases when going upon dimerization into bithiophene.

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Femtosecond Time-Resolved Spectroscopic Studies on Thiophene Oligomers

Cited by 56 publications

References 31 publications

Optical spectra from molecules to crystals: Insight from many-body perturbation theory

Optical spectra from molecules to crystals: Insight from many-body perturbation theory

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

Excited state dynamics of thiophene and bithiophene: new insights into theoretically challenging systems

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