S. Haacke

University of Strasbourg, Strasbourg, Alsace, France

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Publications (73)187.28 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Molecular switches based on the N-alkylated indanylidene-pyrroline (NAIP) framework mimic some of the outstanding double bond photoisomerization properties of retinal Schiff bases in rhodopsin, most notably, the occurrence of vibrational coherences in the excited and photoproduct ground states. Focusing on the zwitterionic NAIP switch and using broadband transient absorption spectroscopy, our previous investigation of the Z to E photoisomerization dynamics is now extended to the study of the backward E to Z photoisomerization and to the role of the solvent on the vibrational coherence accompanying the photoreaction. Despite very similar signatures of excited-state vibrational coherence and similar isomerization times, the backward reaction has a significantly smaller isomerization yield than the forward reaction, and most interestingly, does not display ground state coherences. This indicates that both the quantum yield and vibrational dephasing depend critically on the photochemical reaction path followed to reach the ground potential energy surface. In addition, investigation of the effect of the solvent viscosity shows that vibrational dephasing is mainly an intramolecular process.
    New Journal of Physics 10/2013; 15(10):105022. · 4.06 Impact Factor
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    ABSTRACT: Photoisomerizing molecular switches convert light energy into mechanical energy at the molecular level. In coherent photoisomerization, the energy is impulsively funnelled into a small number of vibrational modes, so that vibrational wave packets are observed throughout the reaction. Observing wavepackets in the photoproduct ground ground state, which requires the excited state coherence to survive the passage through the conical intersection, was so far observed for rhodopsin (Rho) only. However, using ultrafast pump-probe transient absorption (TA) spectroscopy it was recently demonstrated to occur also in small artificial photoswitches in solution. These were based on an indanylidene-pyrroline (IP) chemical skeleton, where a pyrole ring is linked to an indanone moiety via a single double carbonyl bond C1'=C1. It was shown by ab initio quantum chemical calculations that IP derivatives are able to reproduce the excited state (S1) potential energy surface of retinal in rhodopsin.
    The European Conference on Lasers and Electro-Optics; 05/2013
  • International Quantum Electronics Conference; 05/2013
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    ABSTRACT: Steady-state fluorescence measurements of the first excited state of the anabaena sensory rhodopsin (ASR), and Bacteriorhodopsin are reported for different light stabilization conditions, including the dark-adapted state. We determine the fluorescence spectra of both all-trans (AT), and 13-cis (13C) protonated Schiff base of retinal, and compare the effect of the proteins. Referenced against the fluorescence quantum yield of AT-bR (2.5 × 10-4) we find for AT-ASR, 13C-ASR, and 13C-bR the values of 3.3 × 10-4, 0.8 × 10-4, and 1.7 × 10-4, respectively. Using reported excited state lifetimes, the radiative rates are deduced, and their differences discussed on the basis of a configuration-dependent oscillator strength.
    Chemical Physics Letters 01/2013; 587:75-80. · 2.15 Impact Factor
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    ABSTRACT: Ultrafast transient absorption spectroscopy is performed on a novel donor-acceptor-donor triad made of two identical bisthiophene derivatives as electron donors and a central perylenediimide moiety as electron acceptor. The triad is extended at both ends by covalently bound siloxane chains that confer self-organisation into thin smectic films at ambient temperature. When diluted in chloroform, selective excitation of the donor moiety leads to resonance energy transfer within 130 fs to the acceptor moiety, followed by the formation of a charge transfer (CT) state in ~3 ps. The CT state recombines entirely on a 55 ps time scale. In the liquid crystal films, excitonic intermolecular coupling leads to significant changes in the dynamics. Most remarkably, ultrafast intra- and intermolecular CT state formation occurs in about 60 fs, i.e. on a time scale comparable to electronic coherence times. While the intra-molecular CT states recombine on the same time scale as in solution or even faster, inter-molecular CT states live for about 1 ns. Last, triplet states of the perylenediimide moiety dominate the differential absorption after ~1 ns. We anticipate that the fast recombination of intra-molecular CT states and the triplet state formation may severely limit the photo-current in these materials.
    Physical Chemistry Chemical Physics 11/2011; 14(1):273-9. · 4.20 Impact Factor
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    ABSTRACT: A novel femtosecond fluorescence experiment based on type II difference frequency mixing is demonstrated. This approach is particularly interesting for near-UV emitting biological chromophores like amino acids and nucleotides, as the fluorescence is converted into the spectral range where CCD have their highest quantum efficiencies. The method is implemented with a 5-kHz amplified Ti:Sapphire laser system and first results obtained with 2,5-diphenyloxazole (PPO) in ethanol are reported.
    Journal of Physics Conference Series 03/2011; 277(1):012017.
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    ABSTRACT: Triggered by the quest for new organic materials and micro-structures for photovoltaic applications, a novel class of donor-acceptor-donor (DAD) triads extended with siloxane chains has been synthesized in our labs. Because of the siloxane chains, the molecules self-organize into a smectic liquid crystal phase, resulting in a stacking of the DAD cores.We report here a preliminary study of the ultrafast dynamics of energy and charge transfer studied by femtosecond broadband transient absorption experiments on isolated triads in chloroform.
    Journal of Physics Conference Series 03/2011; 276(1):012006.
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    ABSTRACT: The excited state quenching and photoproduct formation of tryptophan in water is studied by femtosecond transient absorption experiments covering the near-UV and Vis range of wavelengths. The quenching of the excited state absorption occurs simultaneously with the rise of a photoproduct characterized by two absorption bands at 350 nm and 425 nm. Both processes are characterized by the same biexponential kinetics, and the time constants found are in excellent agreement with previous time-resolved fluorescence measurements. By varying the pH and comparing with the transient spectra of Trp incorporated in a peptide where electron transfer is the dominant quenching mechanism, we suggest that the photoproduct is a zwitterionic form of Trp with the indole moiety protonated, formed via excited state proton transfer from the side chain amine group, in agreement with conclusions drawn from nanosecond experiments. The present work thus fills the gap between ultrafast fluorescence decay and nanosecond flash photolysis experiments, and pinpoints Trp's fluorescence quenching mechanism at acidic and neutral pH.
    Physical Chemistry Chemical Physics 12/2010; 12(48):15744-50. · 4.20 Impact Factor
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    ABSTRACT: Femtosecond UV-VIS and mid-IR experiments show that a new class of biomimetic photoswitches photo-isomerizes in less than 300 fs. In close analogy to rhodopsin, the isomerization is driven by ultrafast motion along the stretch and the torsional coordinates.
    01/2009;
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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;
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    ABSTRACT: A comparative study of absorption spectroscopy at 100 K has been performed on three-dimensional crystals of bacteriorhodopsin extracted from a lipidic cubic phase and on native purple membrane. A modified microspectrophotometer has been designed which yields absorption data with a high signal-to-noise ratio and remarkable reproducibility. Excellent agreement of the absorption spectra of the three-dimensional crystals and the purple membrane is observed provided that a rigorous crystal-handling procedure is followed. This result supports the equivalence of the protein structure in both the cubic phase crystals and the native purple membrane. On the other hand, it is shown that dramatic deviations of the crystal spectrum can be induced by minor changes in the extraction method. Exposure to air at room temperature can lead within a short time to an irreversible dehydration manifested by a distinct species with an absorption maximum at 500 nm. Exposure of the crystals to a buffer with lower ionic strength than the crystallization solution produces a different spectral form with an absorption maximum at 477 nm, which was assigned to a distorted protein conformation induced by osmotic stress. The extreme sensitivity of these crystals to experimental conditions is relevant for X-ray structural studies, in particular as different experimental treatments are implemented to trap the intermediates of the protein's photocycle.
    Acta Crystallographica Section D Biological Crystallography 05/2006; 62(Pt 4):368-74. · 14.10 Impact Factor
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    ABSTRACT: A visible-pump/UV-probe transient absorption is used to characterize the ultrafast dynamics of bacteriorhodopsin with 80-fs time resolution. We identify three spectral components in the 265- to 310-nm region, related to the all-trans retinal, tryptophan (Trp)-86 and the isomerized photoproduct, allowing us to map the dynamics from reactants to products, along with the response of Trp amino acids. The signal of the photoproduct appears with a time delay of approximately 250 fs and is characterized by a steep rise ( approximately 150 fs), followed by additional rise and decay components, with time scales characteristic of the J intermediate. The delayed onset and the steep rise point to an impulsive formation of a transition state on the way to isomerization. We argue that this impulsive formation results from a splitting of a wave packet of torsional modes on the potential surface at the branching between the all-trans and the cis forms. Parallel to these dynamics, the signal caused by Trp response rises in approximately 200 fs, because of the translocation of charge along the conjugate chain, and possible mechanisms are presented, which trigger isomerization.
    Proceedings of the National Academy of Sciences 04/2006; 103(11):4101-6. · 9.81 Impact Factor
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    ABSTRACT: The ultrafast evolution of the electric field within bacteriorhodopsin was measured by monitoring the absorption changes of a tryptophan residue after excitation of retinal. The Trp absorption decreases within the first 200 femtoseconds and then recovers on time scales typical for retinal isomerization and vibrational relaxation. A model of excitonic coupling between retinal and tryptophans shows that the signal reflects a gradual rise of the retinal difference dipole moment, which precedes and probably drives isomerization. The results suggest an intimate connection between the progressive dipole moment change and the retinal skeletal changes reported over the same time scale.
    Science 09/2005; 309(5736):917-20. · 31.20 Impact Factor
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    ABSTRACT: Femtosecond photoluminescence (PL) up-conversion studies in polychromatic mode and laser-power-dependence studies of the PL were carried out on colloidal solutions of CdSe quantum dots with diameters ranging from 2.4to4nm . The main features of the spectra consist, in addition to the band-gap luminescence, of three bands, one 120-130meV and another 30-40meV at low energy to the band-gap luminescence, while the third lies 220-260meV higher in energy. The first band is attributed to a positively charged biexciton and the second to a neutral biexciton, while the blue band is attributed to a neutral triexciton. These assignments are based on the energetics, the lifetimes, and the pump-power dependence of the various bands. The energetics and lifetimes are in good agreement with the theoretical studies present in literature.
    Physical Review B 05/2005; · 3.66 Impact Factor
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    ABSTRACT: The ultrafast spectral evolution of the fluorescence of the all-trans protonated Schiff base of retinal (PSBR) in alcs. with different polarity was studied using the fluorescence up-conversion technique in a \"polychromatic mode\". Results reveal that vibrational cooling is the dominant contribution to the total Stokes shift of PSBR's in alcs. The total Stokes shifts are very large: 7.9 +- 100/cm for PSBR/methanol and 6.87 +- 100/cm for octanol. Another striking observation is the .apprx.30% smaller width of the fluorescence spectrum of methanol compared with other alcs. On the other hand, dielec. solvation has only minor contribution to the total Stokes shift, irresp. of the solvent. In both solvents, the time-zero spectrum is already red-shifted by more than 6.0/cm with respect to the max. of absorption. [on SciFinder (R)]
    01/2003;
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    ABSTRACT: We present the results of a study of the dynamics of trions and excitons in a CdTe modulationdoped quantum well as a function of temperature in the low-density regime. Using three-pulse four-wave mixing technique, we show that, at low temperature, these quasi-particles are inhomo-geneously broadened and localized due to disorder effects. At higher temperatures, trions and excitons are mobile and their homogeneous broadening is largely increased as a result of acoustic phonon scattering. Consistently, time-resolved luminescence measurements also reveal a free-particle character for trions at high temperatures.
    physica status solidi (b) 11/2002; · 1.49 Impact Factor
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    ABSTRACT: The dynamics of excitons and trions in CdTe modulation-doped quantum wells are studied as a function of temperature by three-pulse four-wave mixing experiments. It is shown that trions are localized by interface roughness scattering and/or by the remote ionized donor potential at low temperature in the low-density regime. The diffusivity of excitons and trions increases with temperature but their mobilities are limited by acoustical phonon scattering, The coherence study reveals that the system is inhomogeneously broadened at low temperature and becomes nearly homogeneous as the temperature is increased.
    physica status solidi (a) 04/2002; · 1.21 Impact Factor
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    ABSTRACT: The spectrally and temporally resolved fluorescence properties of native bacteriorhodopsin (bR) and bR reconstituted with a nonisomerizing analog of the retinal Schiff base (bR5.12) are examined. The first attempt to experimentally monitor the excited state relaxation processes in both type of pigments using ultrafast fluorescence spectroscopy is reported. The fluorescence is emitted from retinal molecules in an all-trans configuration. Substantial energy relaxation involves very fast intramolecular and intermolecular vibrational modes and these are shown to occur on a time scale faster than isomerization. The possible contribution of dielectric interaction between the retinal Schiff base and the protein environment for the excited state energy relaxation is discussed.
    Biopolymers 02/2002; 67(4-5):306-9. · 2.88 Impact Factor
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    ABSTRACT: Time-integrated fluorescence expts. on native bacteriorhodopsin and on its non-isomerizing form bR5.12 are reported. The exptl. set-up was designed such as to observe emission exclusively from the excited state intermediate I-460. We obtain the first systematic investigation of the fluorescence spectra as a function of the excitation wavelength tuned throughout the entire absorption band of bR. An important finding is that the position of the fluorescence max. does not show a systematic shift when the excitation wavelength is shortened. For excitation with high excess energy, we observe a broadening of the blue wing of the bR fluorescence, indicating incomplete vibrational energy relaxation on the time scale of the lifetime of I-460. Due to a much longer excited state lifetime, vibrational energy relaxation is more effective in bR5.12 and the fluorescence spectra are much less dependent on excitation wavelength. The results are placed in the general framework of thermalization between the retinal chromophore and the protein environment, and are compared with information obtained by femtosecond expts. [on SciFinder (R)]
    Physical Chemistry Chemical Physics 01/2002; · 4.20 Impact Factor
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    ABSTRACT: Excitons and trions in a CdTe modulation-doped quantum well are investigated by picosecond three-pulse four-wave mixing experiments as a function of temperature in the low-density regime. We show that trions are mobile for high enough temperatures. The diffusivity of trions and excitons increases with temperature but, like their mobilities, is limited by acoustic-phonon scattering. Consistently, studying the decay of the interband coherence reveals an increase of the homogeneous broadening as the temperature is raised. At low temperatures, excitonic complexes are localized by both interface roughness scattering and by the electrostatic potential due to remote ionized donors.
    Physical review. B, Condensed matter 01/2002; · 3.77 Impact Factor

Publication Stats

653 Citations
187.28 Total Impact Points

Institutions

  • 2010–2011
    • University of Strasbourg
      • Institut de physique et chimie des matériaux de Strasbourg (IPCMS)
      Strasbourg, Alsace, France
  • 1996–2006
    • École Polytechnique Fédérale de Lausanne
      • • Institut des sciences et ingénierie chimiques
      • • Institut de théorie des phénomènes physiques
      Lausanne, Vaud, Switzerland
  • 2000–2002
    • University of Lausanne
      Lausanne, Vaud, Switzerland
  • 1996–2000
    • Eawag: Das Wasserforschungs-Institut des ETH-Bereichs
      Duebendorf, Zurich, Switzerland
  • 1993
    • French National Centre for Scientific Research
      Lutetia Parisorum, Île-de-France, France