A Theoretical Study on the Low‐Lying Excited States of 2,2′:5′,2′′‐Terthiophene and 2,2′:5′,2′′:5′′,2′′′‐Quaterthiophene

Rubio, Mercedes; Merchán, Manuela; Ortı́, Enrique

doi:10.1002/cphc.200400487

Cited by 39 publications

(58 citation statements)

References 65 publications

(233 reference statements)

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“…14,25 The nature of this CT-type singlet state would obviously involve some contribution from σ f π* transitions. 25 A more recent and alternative interpretation, based on ab initio studies 32 computed for R3, suggests a large energy difference between the S 1 and T 1 states and proposed that intersystem crossing would involve coupling between the T 2 and S 1 states in its equilibrium geometry and that for tetrathiophene (R4) the higher energy gap between S 1 and T 2 together with symmetry considerations 32 would lead to a less favored spin-orbit coupling which would explain the decrease in the φ T value 14 from R3 to R4.…”

Section: Discussionmentioning

confidence: 99%

Spectral and Photophysical Studies on Cruciform Oligothiophenes in Solution and the Solid State

et al. 2006

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The photophysical and spectroscopic properties of a new class of oligothiophene derivatives, designated as cruciform oligomers, have been investigated in solution (room and low temperature) and in the solid state (as thin films in Zeonex matrixes). The study comprises absorption, emission, and triplet-triplet absorption spectra, together with quantitative measurements of quantum yields (fluorescence, intersystem crossing, internal conversion, and singlet oxygen formation) and lifetimes. The overall data allow the determination of the rate constants for all decay processes. From these, several conclusions are drawn. First, in solution, the main deactivation channels for the compounds are the radiationless processes: S 1 ' S 0 internal conversion and S 1 ' T 1 intersystem crossing. Second, in general, in the solid state, the fluorescence quantum yields decrease relative to solution. A comparison is made with the analogous linear R-oligothiophenes, revealing a lower fluorescence quantum efficiency and, in contrast to the normal oligothiophenes, that internal conversion is an important channel for the deactivation of the singlet excited state. Replacement of thiophene by 1,4-phenylene units in the longer-sized cruciform oligomer increases the fluorescence efficiency. The highly efficient generation of singlet oxygen through energy transfer from the triplet state (S ∆ ≈ 1) provides support for the measured intersystem crossing quantum yields and suggests that reaction with this may be an important pathway to consider for degradation of devices produced with these compounds.

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Section: Discussionmentioning

confidence: 99%

Spectral and Photophysical Studies on Cruciform Oligothiophenes in Solution and the Solid State

et al. 2006

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“…For the energy calculations of 3T the complete p-valence active space was used (CAS(18/15)). Like in a previous study of 3T 59 the CASSCF optimizations of the excited states were performed with a smaller active space, 12 electrons/12 orbitals, where the three deepest p-orbitals were kept inactive. For the optimization of the S 1 /S 0 conical intersection and the T 1 /S 0 intersection of 3T this active space was extended by one pair of s-orbitals (s/s*).…”

Section: Computational Detailsmentioning

confidence: 99%

Deactivation pathways of thiophene and oligothiophenes: internal conversion versus intersystem crossing

Kölle

Schnappinger

Vivie‐Riedle

2016

Phys. Chem. Chem. Phys.

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Oligothiophenes and polythiophenes are building blocks of organic-based energy conversion materials. Therefore the lifetime of the excited states plays a central role. As a first step to understand the factors influencing the performance, we investigated the deactivation processes from the first excited state S1 of thiophene and small oligothiophenes containing up to four rings using quantum chemical calculations. For thiophene a low-lying S1/S0 conical intersection seam is easily accessible and drives the fast internal conversion. In oligothiophenes barriers inhibit this passage while deactivation pathways via intersystem crossing channels open. The first one is responsible for the high triplet quantum yields and takes place shortly after the Franck-Condon region. The second one occurs in the vicinity of a local S1 minimum. The calculated spin-orbit coupling strength together with the singlet-triplet energy gaps can explain the decreasing triplet and increasing fluorescence quantum yields for growing chain length. From the triplets the ground state is reachable by inter-ring torsions and T1/S0 intersections. The present results allow a deeper understanding of the deactivation pathways of thiophene and small oligothiophenes and are of potential interest for the photophysics of longer oligothiophenes and polythiophenes used in optical devices.

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“…Complete Active Space (CAS) based methods. 19,23,49,50 In this work we compare molecular geometries obtained from DFT and RICC2 calculations as well as excitation energies obtained for the optimized structures.…”

Section: Introductionmentioning

confidence: 99%

Torsional effects on excitation energies of thiophene derivatives induced by β‐substituents: Comparison between time‐dependent density functional theory and approximated coupled cluster approaches

et al. 2007

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The influence of methyl or phenyl substitution in beta-position of dioxygenated terthiophene and diphenylthiophene on the optical properties is investigated by first-principles calculations. We compare the approximated singles and doubles coupled cluster (CC2) approach with time-dependent density functional theory methods. CC2 reproduces experimental excitation energies with an accuracy of 0.1 eV. We find that the different substituents modify the inter-ring torsional angle which in turn strongly influences the excitation energies. The steric contribution to the excitation energies have been separated from the total substituent effects.

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A Theoretical Study on the Low‐Lying Excited States of 2,2′:5′,2′′‐Terthiophene and 2,2′:5′,2′′:5′′,2′′′‐Quaterthiophene

Cited by 39 publications

References 65 publications

Spectral and Photophysical Studies on Cruciform Oligothiophenes in Solution and the Solid State

Spectral and Photophysical Studies on Cruciform Oligothiophenes in Solution and the Solid State

Deactivation pathways of thiophene and oligothiophenes: internal conversion versus intersystem crossing

Torsional effects on excitation energies of thiophene derivatives induced by β‐substituents: Comparison between time‐dependent density functional theory and approximated coupled cluster approaches

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