Ultrafast excited-state dynamics of phenyleneethynylene oligomers in solution

Duvanel, Guillaume; Grilj, Jakob; Schuwey, Anne; Gossauer, Albert; Vauthey, Eric

doi:10.1039/b702647a

Cited by 46 publications

(78 citation statements)

References 35 publications

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“…This is in qualitative agreement with the observation, considering that the excited-state absorption spectrum of OPEs comprises a broad positive band ranging from about 500-550 nm to more than 700 nm. 49 The amplitude spectrum associated with τ 2 ) 5 ps is very similar to the negative of the OPE/NDI-CSS spectrum. This time constant is thus assigned to the buildup of the OPE/NDI-CSS population as well, but upon direct excitation of the NDIs at 400 nm (pathway 4 in Figure 5).…”

Section: Resultsmentioning

confidence: 68%

“…The intensity of this emission is so weak that only upper limit values of Φ fl can be estimated (Table 1). OPEs are known to be strong fluorescers, with radiative rate constants, k rad , on the order of 10 9 s -1 , 49 and therefore the negligible OPE-LES f S 0 fluores- cence, together with the small excitation energy transfer efficiencies, reveals the existence of another highly effective deactivation channel of the OPE-LES. Time-Resolved Fluorescence.…”

Section: Resultsmentioning

confidence: 99%

“…It exhibits a negative band below 450 nm that can be interpreted as a bleach of the S 0 f OPE-LES transition and a broad positive band at longer wavelength that is similar to the excited-state absorption spectrum of OPE. 49 Thus, τ 1 can be undoubtedly ascribed to the decay of the OPE-LES population. In principle, two decay pathways can be envisaged: direct CS with an NDI to the OPE/NDI-CSS (pathway 3) and excitation energy transfer from the OPE scaffold to an NDI (pathway 1).…”

Section: Resultsmentioning

confidence: 99%

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Excited-State Dynamics of Hybrid Multichromophoric Systems: Toward an Excitation Wavelength Control of the Charge Separation Pathways

et al. 2009

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The photophysical properties of two hybrid multichromophoric systems consisting of an oligophenylethynyl (OPE) scaffold decorated by 10 red or blue naphthalene diimides (NDIs) have been investigated using femtosecond spectroscopy. Ultrafast charge separation was observed with both red and blue systems. However, the nature of the charge-separated state and its lifetime were found to differ substantially. For the red system, electron transfer occurs from the OPE scaffold to an NDI unit, independently of whether the OPE or an NDI is initially excited. However, charge separation upon OPE excitation is about 10 times faster, and takes place with a 100 fs time constant. The average lifetime of the ensuing charge-separated state amounts to about 650 ps. Charge separation in the blue system depends on which of the OPE scaffold or an NDI is excited. In the first case, an electron is transferred from the OPE to an NDI and the hole subsequently shifts to another NDI unit, whereas in the second case symmetry-breaking charge separation between two NDI units occurs. Although the charges are located on two NDIs in both cases, different recombination dynamics are observed. This is explained by the location of the ionic NDI moieties that depends on the charge separation pathway, hence on the excitation wavelength. The very different dynamics observed with red and blue systems can be accounted for by the oxidation potentials of the respective NDIs that are higher and lower than that of the OPE scaffold. Because of this, the relative energies of the two charge-separated states (hole on the OPE or an NDI) are inverted.

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Section: Resultsmentioning

confidence: 68%

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

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Excited-State Dynamics of Hybrid Multichromophoric Systems: Toward an Excitation Wavelength Control of the Charge Separation Pathways

et al. 2009

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“…Similar effects have also been reported with polyphenylenethynylenes. 45,46 The fact that the mirror image relationship exists in protic solvents can be explained by the formation of H-bonds with the solvents that restrict the twisting motion of the nitro group and thus reduces torsional disorder.…”

Section: Discussionmentioning

confidence: 99%

Excited-State Dynamics of Nitroperylene in Solution: Solvent and Excitation Wavelength Dependence

2008

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The photophysics and excited-state dynamics of nitroperylene (NPe) in solvents of various polarities and viscosities, including a room-temperature ionic liquid, have been investigated by femtosecond-resolved transient absorption spectroscopy. The excited-state absorption spectrum was found to depend substantially on solvent polarity. In the most polar solvents, it is very similar to that of the NPe radical cation generated upon bimolecular quenching by an electron acceptor, denoting a substantial charge-transfer character of the S 1 state. Contrary to smaller nitroaromatic compounds, NPe in the S 1 state does not undergo ultrafast intersystem crossing (ISC) but decays mainly by internal conversion (IC). In nonprotic solvents, IC involves low-frequency modes with large amplitude motion associated with the nitro group and depends on both the solvent viscosity and polarity. It takes place on a 100 ps time scale in acetonitrile, while in cyclohexane, it is slow enough for ISC to become competitive. Moreover, both the fluorescence quantum yield and the excited-state dynamics were found to differ, depending on which side of the S 0 -S 1 absorption band excitation was performed. This dependence is explained by the inhomogeneous nature of the absorption spectrum arising from a distribution of twist angles of the nitro group relative to the aromatic plane. On the other hand, such excitation wavelength effects were not observed in protic solvents, where the excited-state lifetime was found to be substantially shorter than that in nonprotic solvents. This behavior is rationalized in terms of a H-bonding interaction, which limits the torsional disorder of NPe and favors ultrafast nonradiative deactivation of the excited state. Transient absorption measurements performed for comparative purpose with nitropyrene in acetonitrile confirm the occurrence of ultrafast ISC in smaller nitroaromatic compounds.

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“…The experimental setup for TA spectroscopy has already been described in detail elsewhere. 17,18 Briefly, the excitation pulses were generated by a home-built noncollinear optical parametric amplifier (NOPA) fed by a standard Ti:Sapphire femtosecond amplified system (Spitfire, Spectra Physics) working at a 1 kHz repetition rate. The central wavelength of the pulses was at 520 nm, their duration was about 50 fs and the energy at the sample position was between 0.8 and 1.5 μJ.…”

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confidence: 99%

Ultrafast Excited-State Dynamics of Eosin B: A Potential Probe of the Hydrogen-Bonding Properties of the Environment

2011

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The photophysics of two dyes from the xanthene family, eosin B (EB), and eosin Y (EY) has been investigated in various solvents by femtosecond transient absorption spectroscopy, first, to clarify the huge disparity of the EB fluorescence lifetimes reported in literature, and, second, to understand the mechanism responsible for the ultrafast excited-state deactivation of EB in water. The excited-state lifetime of EB was found to be much shorter in water and in other protic solvents, due to the occurrence of hydrogen-bond assisted nonradiative deactivation. This mechanism is associated with the hydrogen bonds between the solvent molecules and the nitro groups of EB, which become stronger upon optical excitation due to the charge-transfer character of the excited-state. This process is not operative with EY, where the nitro groups are replaced by bromine atoms. Therefore, the excited-state lifetime of EB in solution is directly related to the strength of the solvent as a hydrogen-bond donor, offering the possibility to build a corresponding scale based on the fluorescence quantum yield or lifetime of EB. This scale of hydrogen-bonding strength could be especially useful for studies of liquid interfaces by time-resolved surface second harmonic generation

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Ultrafast excited-state dynamics of phenyleneethynylene oligomers in solution

Cited by 46 publications

References 35 publications

Excited-State Dynamics of Hybrid Multichromophoric Systems: Toward an Excitation Wavelength Control of the Charge Separation Pathways

Excited-State Dynamics of Hybrid Multichromophoric Systems: Toward an Excitation Wavelength Control of the Charge Separation Pathways

Excited-State Dynamics of Nitroperylene in Solution: Solvent and Excitation Wavelength Dependence

Ultrafast Excited-State Dynamics of Eosin B: A Potential Probe of the Hydrogen-Bonding Properties of the Environment

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