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Chemical Physics 01/2011; · 1.90 Impact Factor
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ABSTRACT: We report on an ultrafast experimental and simulations study of the early relaxation events of photoexcited tryptophan in water. Experimentally, we used fluorescence up-conversion in both polychromatic and single wavelength detection modes in the 300-480 nm range with polarization dependence. We report on the time evolution of the Stokes shift, bandwidth, and anisotropy from tens of femtoseconds to picoseconds. These observables contain signatures of the simultaneous occurrence of intramolecular and solvent-molecule interactions, which we disentangle with the help of nonequilibrium molecular dynamics simulations. We also observe a breakdown of the linear response approximation to describe our results.
The Journal of Physical Chemistry A 09/2010; 114(34):9034-42. · 2.95 Impact Factor
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ABSTRACT: We report on the electronic dephasing times of the nonpolar chromophore diphenylacetylene (DPA) in ethanol and in cyclohexane (polar and nonpolar solvents respectively) by photon echo measurements in the ultraviolet. Contrary to previous reports, we observed sub-100-fs electronic dephasing times for DPA in both solvents. We identify fast dynamics of tau=40+/-10 fs on the photon echo peak shift (PEPS) traces of DPA in ethanol. In addition, we observed a dependence of the PEPS asymptotic value on the temporal chirp of the pulses. We propose a model to describe it in terms of phase-matching condition and beam geometry.
The Journal of chemical physics 08/2010; 133(6):064506. · 3.09 Impact Factor
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ABSTRACT: Instrumentation and Techniques SymposiaUltrafast Electronic and Structural Phenomena in Graphite and GrapheneArticle author querycarbone f [PubMed]
[Google Scholar]kwon o [PubMed]
[Google Scholar]cannizzo a [PubMed]
[Google Scholar]van mourik f [PubMed]
[Google Scholar]chergui m [PubMed]
[Google Scholar]zewail a [PubMed]
[Google Scholar]F Carbonea1, OH Kwona2, A Cannizzoa1, F van Mourika1, M Cherguia1 and AH Zewaila2a1 École Polytechnique Fédérale de Lausanne, Switzerland
Microscopy and Microanalysis 06/2010; 16:494 - 495. · 3.01 Impact Factor
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ABSTRACT: The comparison between UV transient absorption spectra of wild type bacteriorhodopsin and two tryptophan-mutant proteins gives
evidence for the possibility to use tryptophans as ultrafast probes for the photo-induced dipole moment change in retinal
proteins.
12/2008: pages 544-546;
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ABSTRACT: We show a femtosecond fluorescence upconversion setup with broadband detection to measure time-resolved emission spectra in the 300-550 nm range, upon excitation between 250 and 300 nm, with a time resolution of 100 fs. We present time-resolved fluorescence emission spectra of 2,5-diphenyloxazole in solution, which demonstrate the capabilities of the setup.
Optics Letters 01/2008; 32(24):3555-7. · 3.40 Impact Factor
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Journal of Non-Crystalline Solids. 01/2005; 351(21-23):1805-1809.
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Philosophical Magazine. 01/2004; 84(13-16):1651-1657.
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Radiation Measurements. 01/2004; 38(4-6):645-648.
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Journal of Sol-Gel Science and Technology 01/2003; 26:915. · 1.63 Impact Factor
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ABSTRACT: The (sub)-ps relaxation processes in PbSe quantum dots of different sizes were measured by near-IR luminescence upconversion. The early-time spectra are characterized by emission from several low-lying excited states. The direct measurement of the Huang-Rhys factors of the lowest excited states excludes strong electron-phonon coupling in the intraband relaxation. The kinetics point to a fast sequential cascade process between excited states, governed by energy gaps and a quasicontinuous valence-band structure.
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ABSTRACT: The authors present photon echo peak shift and femtosecond fluorescence up-conversion studies of nonpolar solvation dynamics of a simple nonpolar dye p-terphenyl in EtOH and cyclohexane, using excitation in the UV range at 290 nm. The UV fluorescence up-conversion expts. were combined with a polychromatic detection and the results highlight the high sensitivity of this approach to fully characterize the excited state dynamics of the dye. The authors also demonstrate the feasibility of UV photon echo and transient grating and its sensitivity for the detection of nonpolar solvation dynamics by measuring the frequency correlation function of the dye in the ground state. While solvation dynamics in the picosecond regime is obsd. in EtOH, electronic coherence dephasing occurs on timescales faster than 100 fs in EtOH as well as in the nonpolar solvent cyclohexane.
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J. Phys. Chem. Solids 64(2003),2437.
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J. Non-Cryst. Solids 351(2005),1937.
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J. Non-Cryst. Solids 352(2006),2082.
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ABSTRACT: Dizzy cooling: Femtosecond excitation of the singlet states of aqueous [FeII(bpy)3]2+ (bpy=2,2-bipyridine) leads to the formation of a vibrationally hot quintet state that exhibits wave-packet dynamics arising from a chelate-ring and bending mode. The vibrational relaxation involves at least two modes: the FeN stretching mode (see picture) and the coherently excited chelate-ring and bending mode, which relax on different time scales.
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Coord. Chem. Rev. 254(2010)21-22,2677-2686.
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ABSTRACT: The comparison between UV transient absorption spectra of wild type bacteriorhodopsin and two tryptophan-mutant proteins gives evidence for the possibility to use tryptophans as ultrafast probes for the photo-induced dipole moment change in retinal proteins.
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ABSTRACT: The fs-time-resolved study of a small UV dye in different solvents with fluorescence up-conversion and photon-echo techniques in the UV range provides new insight in cooling relaxation and solvation dynamics of non-polar molecules in polar solvents.
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ABSTRACT: The light-induced spin and structure changes upon excitation of the singlet metal-to-ligand charge transfer (1MLCT) state of Fe(II)-polypyridine complexes are investigated in detail in the case of aqueous iron(II)-tris-bipyridine ([FeII(bpy)3]2+) by a combination of ultrafast optical and X-ray spectroscopies. Polychromatic femtosecond fluorescence up-conversion, transient absorption studies in the 290-600nm region and femtosecond X-ray absorption spectroscopy allow us to retrieve the entire photocycle upon excitation of the 1MLCT state from the singlet low-spin ground state (1GS) as the following sequence: 1,3MLCT→5T→1GS, which does not involve intermediate singlet and triplet ligand-field states. The population time of the HS state is found to be ∼150fs, leaving it in a vibrationally hot state that relaxes in 2-3ps, before decaying to the ground state in 650ps. We also determine the structure of the high-spin quintet excited state by picosecond X-ray absorption spectroscopy at the K-edge of Fe. We argue that given the many common electronic (ordering of electronic states) and structural (Fe-N bond elongation in the high-spin state, Fe-N mode frequencies, etc.) similarities between all Fe(II)-polypyridine complexes, the results on the electronic relaxation processes reported in the case of [FeII(bpy)3]2+ are of general validity to the entire family of Fe(II)-polypyridine complexes. © 2009 Elsevier B.V.
