Comparison of the chain length dependence of the singlet- and triplet-excited states of oligofluorenes

Wasserberg, Dorothee; Dudek, Stephen P.; Meskers, Stefan C. J.; Janssen, Raj René

doi:10.1016/j.cplett.2005.06.039

Cited by 70 publications

(78 citation statements)

References 21 publications

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“…It should be noted that similar strong confinement of the T 1 triplet exciton has been observed for platinum polyyne derivatives. [45] This finding and ours are somewhat different to those reported for ethylenedioxythiophene oligomers [46] and oligo(9,9-dihexyloligofluorene-2,7-diyl)s, [47] where the triplet energies gradually decrease with an increase in monomer units. We speculate of the possibility that triple bonds help decouple organic units at the triplet level, but further studies are clearly required to see if this is a general phenomenon.…”

contrasting

confidence: 80%

On the Conjugation Length for Oligo(ethynylnaphthalene)‐Based Molecular Rods

Benniston

Harriman

Rewinska

et al. 2007

Chemistry A European J

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The synthesis is described for a small series of oligomers built from (2, 3, 4 or 6) ethynyl-naphthalene repeat units and end-capped with solubilising 1,2,3-tris-dodecyloxy-benzene groups. These compounds absorb in the near-UV region and exhibit strong fluorescence in both fluid solution and a glassy matrix at 77 K. The spectral profiles are fully consistent with a structurally heterogeneous ground state becoming more planar upon excitation and with the low-temperature glass further stabilising the co-planar orientation. The absorption and fluorescence maxima move towards lower energy with increasing number of repeat units and there is a corresponding increase in the Huang-Rhys factor for the radiative process. The non-radiative rate constants also depend on molecular length and are well explained in terms of the energy-gap law. In contrast, very weak phosphorescence is observed at 77 K for which the peak maximum and lifetime remain insensitive to the number of naphthalene units. The triplet lifetimes recorded at ambient temperature are also independent of the molecular length but the triplet-triplet absorption spectra change throughout the series. These results are discussed in terms of the degree of electronic coupling between adjacent repeat units for each of the relevant excited states. During these studies it was noted that the rate of intersystem crossing to the triplet manifold is but weakly affected by heavy-atom perturbers. A non-fluorescent complex is formed between iodoethane and the molecular rod but the corresponding bimolecular process occurs at well below the diffusion-controlled limit. This behaviour is considered in terms of spin-orbit coupling between the excited states and takes account of the differing conjugation lengths.

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contrasting

confidence: 80%

On the Conjugation Length for Oligo(ethynylnaphthalene)‐Based Molecular Rods

Benniston

Harriman

Rewinska

et al. 2007

Chemistry A European J

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“…21 It is also interesting to note that the alkyl chain in the 9,9′ position strongly influences the decay time associated with fluorene oligomers. [21][22][23] In the case of 9,9-dihexylfluorene-2,2-7-diyl oligomers, the unimeric and trimeric compounds display lifetimes of 0.8 and 0.83 ns, respectively, 23 while with the 2-ethylhexyl group in the 9,9′ position, the dimer and trimer have lifetime values of 789 and 663 ps, respectively. 22 These values are markedly shorter than the nonsubstituted alkyl oligomer.…”

Section: Resultsmentioning

confidence: 99%

Excited State Properties of Oligophenyl and Oligothienyl Swivel Cruciforms

et al. 2008

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A comprehensive study has been undertaken of the electronic spectral and photophysical properties of two oligophenyl (BPH and BPHF) and one oligothienyl (BTF) swivel cruciforms involving measurements of absorption, fluorescence, and phosphorescence spectra, quantum yields of fluorescence (φ F ), phosphorescence (φ Ph ) and triplet formation (φ T ), lifetimes of fluorescence (τ F ) and of the triplet state (τ T ), and quantum yields of singlet oxygen production (φ ∆ ). From these, all radiative k F and radiationless rate constants, k IC and k ISC , have been obtained in solution. The energies of the lowest lying singlet and triplet excited states were also determined at 293 K. Several of the above properties have also been obtained at low temperature and in the solid state (thin films). In general, for the phenyl oligophenyl (BPH) and for the oligothienyl (BTF) compounds, the radiationless decay channels (φ IC + φ ISC ) are the dominant pathway for the excited-state deactivation, whereas with the fluorene based oligophenyl BPHF the radiative route prevails. In contrast to the general rule found for related oligomers (and polymers) where radiative emission from T 1 is absent, with the compounds studied, phosphorescence has been observed for all of the compounds, indicating that this type of functionalization can lead to emissive triplets. Time-resolved fluorescence decays with picosecond resolution revealed multiexponential (bi-and triexponential) decay laws compatible with the existence of more than one species or conformation in the excited state. These results are discussed on the basis of conformational flexibility in the excited state.

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“…The triplet-triplet absorption processes for Cz and F are known. [9,10] In the presence of triplet energy transfer, the triplet-triplet absorption is still present, but in the presence of an efficient electron transfer the triplet-triplet signature should vanish and be replaced by an absorption band related to a charge-separated state; in this work, F À ion (i.e. fluorene anion) and [Cz-CC-Pt-…”

Section: Photophysical Propertiesmentioning

confidence: 97%

“…Thus, it appears that the singlet-singlet energy transfer from Cz to F is relatively inefficient, which strongly argues in favor of a photo-induced electron transfer process to explain the total absence of Cz fluorescence in M3 and P3. Based on this argument and by analogy with other Cz-F systems, [9,10] the quenching of the Cz fluorescence is assigned to an electron transfer from the S 1 state of Cz to F.…”

Section: Photophysical Propertiesmentioning

confidence: 98%

“…[6][7][8] These carbazole (Cz) and fluorene (F) moieties are prone to singlet electron transfer [9,10] and triplet-triplet energy transfer, [9,10] including the case in the Cz-F dyad, [11] and hence bear important properties that have implications in photonics. Recently, heavy-metal bisA C H T U N G T R E N N U N G (ethynyl) linkers were used to form conjugated carbazole-and fluorene-based bis-A C H T U N G T R E N N U N G (ethynyl)-metal polymers (metal = platinum, gold, and mercury), and their emission spectroscopy and photophysics were investigated.…”

Section: Introductionmentioning

confidence: 99%

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Intrachain Electron and Energy Transfer in Conjugated Organometallic Oligomers and Polymers

Aly

Fortin

et al. 2008

Chemistry A European J

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The synthesis of polymers of the type (-Cz-C[triple chemical bond]C-PtL(2)-C[triple chemical bond]C-Cz-X-)(n) along with the corresponding model compounds (Ph-PtL'(2)-C[triple chemical bond]C-Cz)(2)-X-, where Cz=3,3'-carbazole, X=nothing, Cz, or F (2,2'-fluorene), L=PBu(3), and L'=PEt(3) are reported. The electronic spectra (absorption, excitation, emission, and ns-transient spectra) and the photophysics of these species in 2-methyltetrahyrofuran (2MeTHF) at 298 and 77 K are presented. Evidence for singlet electron and triplet energy transfer from the Cz chromophore to the F moiety are provided and discussed in detail. The rate for electron transfer is very fast (>4 x 10(11) s(-1)), whereas that for triplet-triplet energy transfer is much slower (approximately 10(3) s(-1)). This work represents a very rare example of studies that address electronic communication in the backbone of a conjugated organometallic polymer.

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Comparison of the chain length dependence of the singlet- and triplet-excited states of oligofluorenes

Cited by 70 publications

References 21 publications

On the Conjugation Length for Oligo(ethynylnaphthalene)‐Based Molecular Rods

On the Conjugation Length for Oligo(ethynylnaphthalene)‐Based Molecular Rods

Excited State Properties of Oligophenyl and Oligothienyl Swivel Cruciforms

Intrachain Electron and Energy Transfer in Conjugated Organometallic Oligomers and Polymers

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