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Jennifer P. Ogilvie - One of the best experts on this subject based on the ideXlab platform.

  • characterization of vibrational coherence in monomeric bacteriochlorophyll a by two dimensional Electronic Spectroscopy
    Journal of Physical Chemistry Letters, 2018
    Co-Authors: Veronica R Policht, Andrew Niedringhaus, Jennifer P. Ogilvie
    Abstract:

    Bacteriochlorophyll a (BChla) is the most abundant pigment found in the Bacterial Reaction Center (BRC) and light-harvesting proteins of photosynthetic purple and green bacteria. Recent two-dimensional Electronic Spectroscopy (2DES) studies of photosynthetic pigment-protein complexes including the BRC and the Fenna-Matthews-Olson (FMO) complex have shown oscillatory signals, or coherences, whose physical origin has been hotly debated. To better understand the observations of coherence in larger photosynthetic systems, it is important to carefully characterize the spectroscopic signatures of the monomeric pigments. Prior spectroscopic studies of BChla have differed significantly in their observations, with some studies reporting little to no coherence. Here we present evidence of strong coherences in monomeric BChla in isopropanol using 2DES at 77 K. We resolve many modes with frequencies that correspond well with known vibrational modes. We confirm their vibrational origin by comparing the 2D spectroscopic signatures with expectations based on a purely vibrational model.

  • spatially resolved fluorescence detected two dimensional Electronic Spectroscopy probes varying excitonic structure in photosynthetic bacteria
    Nature Communications, 2018
    Co-Authors: Vivek Tiwari, Yassel Acosta Matutes, Alastair T Gardiner, Thomas L C Jansen, Richard J Cogdell, Jennifer P. Ogilvie
    Abstract:

    Conventional implementations of two-dimensional Electronic Spectroscopy typically spatially average over ~1010 chromophores spread over ~104 micron square area, limiting their ability to characterize spatially heterogeneous samples. Here we present a variation of two-dimensional Electronic Spectroscopy that is capable of mapping spatially varying differences in excitonic structure, with sensitivity orders of magnitude better than conventional spatially-averaged Electronic spectroscopies. The approach performs fluorescence-detection-based fully collinear two-dimensional Electronic Spectroscopy in a microscope, combining femtosecond time-resolution, sub-micron spatial resolution, and the sensitivity of fluorescence detection. We demonstrate the approach on a mixture of photosynthetic bacteria that are known to exhibit variations in Electronic structure with growth conditions. Spatial variations in the constitution of mixed bacterial colonies manifests as spatially varying peak intensities in the measured two-dimensional contour maps, which exhibit distinct diagonal and cross-peaks that reflect differences in the excitonic structure of the bacterial proteins.

  • strongly coupled bacteriochlorin dyad studied using phase modulated fluorescence detected two dimensional Electronic Spectroscopy
    Optics Express, 2018
    Co-Authors: Vivek Tiwari, Christine Kirmaier, David F Bocian, Dewey Holten, Yassel Acosta Matutes, Marcin Ptaszek, Arkaprabha Konar, Jennifer P. Ogilvie
    Abstract:

    Fluorescence-detected two-dimensional Electronic Spectroscopy (F-2DES) projects the third-order non-linear polarization in a system as an excited Electronic state population which is incoherently detected as fluorescence. Multiple variants of F-2DES have been developed. Here, we report phase-modulated F-2DES measurements on a strongly coupled symmetric bacteriochlorin dyad, a relevant 'toy' model for photosynthetic energy and charge transfer. Coherence map analysis shows that the strongest frequency observed in the dyad is well-separated from the excited state Electronic energy gap, and is consistent with a vibrational frequency readily observed in bacteriochlorin monomers. Kinetic rate maps show a picosecond relaxation timescale between the excited states of the dyad. To our knowledge this is the first demonstration of coherence and kinetic analysis using the phase-modulation approach to F-2DES.

  • strongly coupled bacteriochlorophyll dyad studied using two dimensional phase modulated fluorescence detected Electronic Spectroscopy
    arXiv: Chemical Physics, 2018
    Co-Authors: Vivek Tiwari, Christine Kirmaier, David F Bocian, Dewey Holten, Yassel Acosta Matutes, Marcin Ptaszek, Arkaprabha Konar, Jennifer P. Ogilvie
    Abstract:

    Fluorescence-detected two-dimensional Electronic Spectroscopy (F-2DES) projects the third-order non-linear polarization in a system as an excited Electronic state population which is incoherently detected as fluorescence. Multiple variants of F-2DES have been developed. However, none have demonstrated analysis of kinetics and coherences routine in photon-echo 2DES. Here, we report phase-modulated F-2DES measurements on a strongly coupled symmetric bacteriochlorin dyad, a relevant 'toy' model for photosynthetic energy and charge transfer. Coherence map analysis shows that the strongest frequency observed in the dyad is well-separated from the excited state Electronic energy gap, and is consistent with a vibrational frequency readily observed in bacteriochlorin monomers. Kinetic rate maps show a picosecond relaxation timescale between the excited states of the dyad. To our knowledge this is the first demonstration of coherence and kinetic analysis using any variant of F-2DES.

  • spatially resolved fluorescence detected two dimensional Electronic Spectroscopy probes varying Electronic couplings in photosynthetic bacteria
    arXiv: Chemical Physics, 2018
    Co-Authors: Vivek Tiwari, Alastair T Gardiner, Richard J Cogdell, Yassel Acostamatutes, Jennifer P. Ogilvie
    Abstract:

    We present a variation of two-dimensional Electronic Spectroscopy that is capable of mapping spatially-varying differences in Electronic couplings using a correlated map of excitation and detection frequencies, with sensitivity orders of magnitude better than conventional spatially-averaged Electronic spectroscopies. The approach performs fluorescence-detection-based fully collinear two-dimensional Electronic Spectroscopy in a microscope, combining femtosecond time-resolution, sub-micron spatial resolution, and the sensitivity of fluorescence detection. We demonstrate the approach on a mixture of photosynthetic bacteria that are known to exhibit variations in Electronic structure with growth conditions. Spatial variations in the constitution of mixed bacterial colonies manifests as spatially-varying peak intensities in the measured two-dimensional contour maps, which exhibit well-resolved Electronic couplings between excited Electronic states of the bacterial proteins.

Gregory S. Engel - One of the best experts on this subject based on the ideXlab platform.

  • disentanglement of excited state dynamics with implications for fret measurements two dimensional Electronic Spectroscopy of a bodipy functionalized cavitand
    Chemical Science, 2018
    Co-Authors: John P Otto, Gregory S. Engel, Lili Wang, Igor Pochorovski, Samuel M Blau, Alan Aspuruguzik, Zhenan Bao, Melanie Chiu
    Abstract:

    Forster Resonance Energy Transfer (FRET) is the incoherent transfer of an Electronic excitation from a donor fluorophore to a nearby acceptor. FRET has been applied as a probe of local chromophore environments and distances on the nanoscale by extrapolating transfer efficiencies from standard experimental parameters, such as fluorescence intensities or lifetimes. Competition from nonradiative relaxation processes is often assumed to be constant in these extrapolations, but in actuality, this competition depends on the donor and acceptor environments and can, therefore, be affected by conformational changes. To study the effects of nonradiative relaxation on FRET dynamics, we perform two-dimensional Electronic Spectroscopy (2DES) on a pair of azaboraindacene (BODIPY) dyes, attached to opposite arms of a resorcin[4]arene cavitand. Temperature-induced switching between two equilibrium conformations, vase at 294 K to kite at 193 K, increases the donor–acceptor distance from 0.5 nm to 3 nm, affecting both FRET efficiency and nonradiative relaxation. By disentangling different dynamics based on lifetimes extracted from a series of 2D spectra, we independently observe nonradiative relaxation, FRET, and residual fluorescence from the donor in both vase to kite conformations. We observe changes in both FRET rate and nonradiative relaxation when the molecule switches from vase to kite, and measure a significantly greater difference in transfer efficiency between conformations than would be determined by standard lifetime-based measurements. These observations show that changes in competing nonradiative processes must be taken into account when highly accurate measurements of FRET efficiency are desired.

  • communication coherences observed in vivo in photosynthetic bacteria using two dimensional Electronic Spectroscopy
    Journal of Chemical Physics, 2015
    Co-Authors: Peter D Dahlberg, Graham J Norris, Cheng Wang, Subha Viswanathan, Ved P Singh, Gregory S. Engel
    Abstract:

    Energy transfer through large disordered antenna networks in photosynthetic organisms can occur with a quantum efficiency of nearly 100%. This energy transfer is facilitated by the Electronic structure of the photosynthetic antennae as well as interactions between Electronic states and the surrounding environment. Coherences in time-domain Spectroscopy provide a fine probe of how a system interacts with its surroundings. In two-dimensional Electronic Spectroscopy, coherences can appear on both the ground and excited state surfaces revealing detailed information regarding Electronic structure, system-bath coupling, energy transfer, and energetic coupling in complex chemical systems. Numerous studies have revealed coherences in isolated photosynthetic pigment-protein complexes, but these coherences have not been observed in vivo due to the small amplitude of these signals and the intense scatter from whole cells. Here, we present data acquired using ultrafast video-acquisition gradient-assisted photon echo Spectroscopy to observe quantum beating signals from coherences in vivo. Experiments were conducted on isolated light harvesting complex II (LH2) from Rhodobacter sphaeroides, whole cells of R. sphaeroides, and whole cells of R. sphaeroides grown in 30% deuterated media. A vibronic coherence was observed following laser excitation at ambient temperature between the B850 and the B850∗ states of LH2 in each of the 3 samples with a lifetime of ∼40-60 fs.

  • exploring size and state dynamics in cdse quantum dots using two dimensional Electronic Spectroscopy
    Journal of Chemical Physics, 2014
    Co-Authors: Justin R Caram, Haibin Zheng, Peter D Dahlberg, Brian S Rolczynski, Graham B Griffin, Dmitriy S Dolzhnikov, Dmitri V Talapin, Gregory S. Engel
    Abstract:

    Development of optoElectronic technologies based on quantum dots depends on measuring, optimizing, and ultimately predicting charge carrier dynamics in the nanocrystal. In such systems, size inhomogeneity and the photoexcited population distribution among various excitonic states have distinct effects on electron and hole relaxation, which are difficult to distinguish spectroscopically. Two-dimensional Electronic Spectroscopy can help to untangle these effects by resolving excitation energy and subsequent nonlinear response in a single experiment. Using a filament-generated continuum as a pump and probe source, we collect two-dimensional spectra with sufficient spectral bandwidth to follow dynamics upon excitation of the lowest three optical transitions in a polydisperse ensemble of colloidal CdSe quantum dots. We first compare to prior transient absorption studies to confirm excitation-state-dependent dynamics such as increased surface-trapping upon excitation of hot electrons. Second, we demonstrate fast band-edge electron-hole pair solvation by ligand and phonon modes, as the ensemble relaxes to the photoluminescent state on a sub-picosecond time-scale. Third, we find that static disorder due to size polydispersity dominates the nonlinear response upon excitation into the hot electron manifold; this broadening mechanism stands in contrast to that of the band-edge exciton. Finally, we demonstrate excitation-energy dependent hot-carrier relaxation rates, and we describe how two-dimensional Electronic Spectroscopy can complement other transient nonlinear techniques.

  • excited and ground state vibrational dynamics revealed by two dimensional Electronic Spectroscopy
    Journal of Chemical Physics, 2012
    Co-Authors: Justin R Caram, Andrew F Fidler, Gregory S. Engel
    Abstract:

    Broadband two-dimensional Electronic Spectroscopy (2DES) can assist in understanding complex Electronic and vibrational signatures. In this paper, we use 2DES to examine the Electronic structure and dynamics of a long chain cyanine dye (1,1-diethyl-4,4-dicarbocyanine iodide, or DDCI-4), a system with a vibrational progression. Using broadband pulses that span the resonant Electronic transition, we measure two-dimensional spectra that show a characteristic six peak pattern from coherently excited ground and excited state vibrational modes. We model these features using a spectral density formalism and the vibronic features are assigned to Feynman pathways. We also examine the dynamics of a particular set of peaks demonstrating anticorrelated peak motion, a signature of oscillatory wavepacket dynamics on the ground and excited states. These dynamics, in concert with the general structure of vibronic two-dimensional spectra, can be used to distinguish between pure Electronic and vibrational quantum coherences.

  • single shot gradient assisted photon echo Electronic Spectroscopy
    Journal of Physical Chemistry A, 2011
    Co-Authors: Elad Harel, Andrew F Fidler, Gregory S. Engel
    Abstract:

    Two-dimensional Electronic Spectroscopy (2D ES) maps the Electronic structure of complex systems on a femtosecond time scale. While analogous to multidimensional NMR Spectroscopy, 2D optical Spectroscopy differs significantly in its implementation. Yet, 2D Fourier spectroscopies still require point-by-point sampling of the time delay between two pulses responsible for creating quantum coherence among states. Unlike NMR, achieving the requisite phase stability at optical frequencies between these pulse pairs remains experimentally challenging. Nonetheless, 2D optical Spectroscopy has been successfully demonstrated by combining passive and active phase stabilization along with precise control of optical delays and long-term temperature stability, although the widespread adoption of 2D ES has been significantly hampered by these technical challenges. Here, we exploit an analogy to magnetic resonance imaging (MRI) to demonstrate a single-shot method capable of acquiring the entire 2D spectrum in a single laser shot using only conventional optics. Unlike point-by-point sampling protocols typically used to record 2D spectra, this method, which we call GRadient-Assisted Photon Echo (GRAPE) Spectroscopy, largely eliminates phase errors while reducing the acquisition time by orders of magnitude. By incorporating a spatiotemporal encoding of the nonlinear polarization along the excitation frequency axis of the 2D spectrum, GRAPE Spectroscopy achieves no loss in signal while simultaneously reducing overall noise. Here, we describe the principles of GRAPE Spectroscopy and discuss associated experimental considerations.

Graham R Fleming - One of the best experts on this subject based on the ideXlab platform.

  • lineshape characterization for excitons in monolayer ws2 by two dimensional Electronic Spectroscopy
    Nanoscale Advances, 2020
    Co-Authors: Chunan Chen, Zhuquan Zhang, Daniele M Monahan, Graham R Fleming
    Abstract:

    The optical properties of monolayer transition metal dichalcogenides (TMDCs), an important family of two-dimensional (2D) semiconductors for optoElectronic application, are dominated by the two excitons A (XA) and B (XB) located at the K/K’s valleys. The lineshape of the excitons is an indicator of the interaction of the excitons and the other particles and also largely determines the performance of TMDC-based optoElectronic devices. In this work, we apply 2D Electronic Spectroscopy (2DES), which enables separation of the intrinsic homogeneous linewidth and the extrinsic inhomogeneous linewidth, to dissect the lineshape of XA in monolayer WS2. With a home-built broadband optical parametric amplifier, the 2D spectra give the exciton linewidth values for extensive ranges of excitation density and temperature, reflecting inter-exciton and exciton-phonon interactions. Meanwhile, the time-domain evolution of the lineshape reveals a similar rate of spectral diffusion to that in quantum wells (QWs) based on III-V semiconductors.

  • pathways of energy flow in lhcii from two dimensional Electronic Spectroscopy
    Journal of Physical Chemistry B, 2009
    Co-Authors: Gabriela S Schlaucohen, Tessa R. Calhoun, Elizabeth L Read, Naomi S Ginsberg, Matteo Ballottari, Roberto Bassi, Rienk Van Grondelle, Graham R Fleming
    Abstract:

    Photosynthetic light-harvesting complexes absorb energy and guide photoexcitations to reaction centers with speed and efficacy that produce near-perfect efficiency. Light harvesting complex II (LHCII) is the most abundant light-harvesting complex and is responsible for absorbing the majority of light energy in plants. We apply two-dimensional Electronic Spectroscopy to examine energy flow in LHCII. This technique allows for direct mapping of excitation energy pathways as a function of absorption and emission wavelength. The experimental and theoretical results reveal that excitation energy transfers through the complex on three time scales: previously unobserved sub-100 fs relaxation through spatially overlapping states, several hundred femtosecond transfer between nearby chlorophylls, and picosecond energy transfer steps between layers of pigments. All energy is observed to collect into the energetically lowest and most delocalized states, which serve as exit sites. We examine the angular distribution of optimal energy transfer produced by this delocalized Electronic structure and discuss how it facilitates the exit step in which the energy moves from LHCII to other complexes toward the reaction center.

  • pigment organization and energy level structure in light harvesting complex 4 insights from two dimensional Electronic Spectroscopy
    Journal of Physical Chemistry B, 2009
    Co-Authors: Elizabeth L Read, Gregory S. Engel, Gabriela S Schlaucohen, Toni Georgiou, M Z Papiz, Graham R Fleming
    Abstract:

    Photosynthetic light-harvesting antennae direct energy collected from sunlight to reaction centers with remarkable efficiency and rapidity. Despite their common function, the pigment-protein complexes that make up antenna systems in different types of photosynthetic organisms exhibit a wide variety of structural forms. Some individual organisms express different types of complexes depending on growth conditions. For example, purple photosynthetic bacteria Rp. palustris preferentially synthesize light-harvesting complex 4 (LH4), a structural variant of the more common and widely studied LH2, when grown under low-light conditions. Here, we investigate the ultrafast dynamics and energy level structure of LH4 using two-dimensional (2D) Electronic Spectroscopy in combination with theoretical simulations. The experimental data reveal dynamics on two distinct time scales, consistent with coherent dephasing within approximately the first 100 fs, followed by relaxation of population into lower-energy states on a picosecond time scale. We observe excited state absorption (ESA) features marking the existence of high-energy dark states, which suggest that the strongest dipole-dipole coupling in the complex occurs between bacteriochlorophyll transition dipole moments in an in-line geometry. The results help to refine the current understanding of the pigment organization in the LH4 complex, for which a high-resolution crystal structure is not yet available.

  • coherence quantum beats in two dimensional Electronic Spectroscopy
    Journal of Physical Chemistry A, 2008
    Co-Authors: Yuanchung Cheng, Graham R Fleming
    Abstract:

    We study the coherence quantum beats in two-dimensional (2D) Electronic Spectroscopy of a coupled dimer system using a theoretical method based on a time-nonlocal quantum master equation and a recently proposed scheme for the evaluation of the third-order photon echo polarization [Gelin, M. F.; Egorova, D.; Domcek, W. J. Chem. Phys. 2005, 123, 164112]. The simulations show that the amplitude and peak shape beating in the 2D spectra is a result of the interplay between the rephasing and non-rephasing contributions to the 2D signals and can be used to elucidate the coherence dynamics in a multichromophoric system. In addition, the results suggest that the rephasing and non-rephasing 2D spectra contain complementary information, and a study of both of them could provide more dynamical information from 2D Electronic Spectroscopy.

  • 2D Fourier Transform Electronic Spectroscopy of Photosynthetic Reaction Centers: Mapping coupling in the B band
    15th International Conference on Ultrafast Phenomena, 2006
    Co-Authors: Gregory S. Engel, Tomáš Mančal, Tessa R. Calhoun, Donatas Zigamantas, Hohjai Lee, Graham R Fleming
    Abstract:

    The B800 band of the reaction center complex of Rhodobacter sphaeroides has been probed with two-dimensional Fourier transform Electronic Spectroscopy using 40 fs pulses and evidence for coupling within the band will be presented.

Donatas Zigmantas - One of the best experts on this subject based on the ideXlab platform.

  • Two-Dimensional Electronic Spectroscopy Reveals Ultrafast Energy Diffusion in Chlorosomes
    2016
    Co-Authors: Jakub Dostál, Tomáš Mančal, Ramu-nas Augulis, František Vácha, Jakub Pšenčík, Donatas Zigmantas
    Abstract:

    Chlorosomes are light-harvesting antennae that enable exceptionally efficient light energy capture and excitation transfer. They are found in certain photosynthetic bacteria, some of which live in extremely low-light environments. In this work, chlorosomes from the green sulfur bacterium Chlorobaculum tepidum were studied by coherent Electronic two-dimensional (2D) Spectroscopy. Previously uncharacterized ultrafast energy transfer dynamics were followed, appearing as evolution of the 2D spectral line-shape during the first 200 fs after excitation. Observed initial energy flow through the chlorosome is well explained by effective exciton diffusion on a sub-100 fs time scale, which assures efficiency and robustness of the process. The ultrafast incoherent diffusion-like behavior of the excitons points to a disordered energy landscape in the chlorosome, which leads to a rapid loss of excitonic coherences between its structural subunits. This disorder prevents observation of excitonic coherences in the experimental data and implies that the chlorosome as a whole does not function as a coherent light-harvester

  • real time observation of multiexcitonic states in ultrafast singlet fission using coherent 2d Electronic Spectroscopy
    Nature Chemistry, 2016
    Co-Authors: Donatas Zigmantas, Artem A Bakulin, Sarah E Morgan, Tom B Kehoe, Mark W Wilson, Alex W Chin, Dassia Egorova, Akshay Rao
    Abstract:

    Singlet fission is the spin-allowed conversion of a spin-singlet exciton into a pair of spin-triplet excitons residing on neighbouring molecules. To rationalize this phenomenon, a multiexcitonic spin-zero triplet-pair state has been hypothesized as an intermediate in singlet fission. However, the nature of the intermediate states and the underlying mechanism of ultrafast fission have not been elucidated experimentally. Here, we study a series of pentacene derivatives using ultrafast two-dimensional Electronic Spectroscopy and unravel the origin of the states involved in fission. Our data reveal the crucial role of vibrational degrees of freedom coupled to Electronic excitations that facilitate the mixing of multiexcitonic states with singlet excitons. The resulting manifold of vibronic states drives sub-100 fs fission with unity efficiency. Our results provide a framework for understanding singlet fission and show how the formation of vibronic manifolds with a high density of states facilitates fast and efficient Electronic processes in molecular systems.

  • the nature of coherences in the b820 bacteriochlorophyll dimer revealed by two dimensional Electronic Spectroscopy
    Physical Chemistry Chemical Physics, 2014
    Co-Authors: Marco Ferretti, Donatas Zigmantas, Ramu-nas Augulis, Vladimir I Novoderezhkin, Elisabet Romero, Anjali Pandit, Rienk Van Grondelle
    Abstract:

    Light-harvesting in photosynthesis is determined by the excitonic interactions in disordered antennae and the coupling of collective Electronic excitations to fast nuclear motions, producing efficient energy transfer with a complicated interplay between exciton and vibrational coherences. Two-dimensional Electronic Spectroscopy (2DES) is a powerful tool to study the presence of these coherences in photosynthetic complexes. However, the unambiguous assignment of the nature of the observed coherences is still under debate. In this paper we apply 2DES to an excitonically coupled bacteriochlorophyll dimer, the B820 subunit of the light harvesting complex 1 (LH1-RC) of R. rubrum G9. Fourier analysis of the measured kinetics and modeling of the spectral responses in a complete basis of Electronic and vibrational states allow us to distinguish between pure vibrational, mixed exciton-vibrational (vibronic), and predominantly exciton coherences. The mixed coherences have been found in a wide range of oscillation frequencies, whereas exciton coherences give the biggest contributions for the frequencies in the 400–550 cm−1 range, corresponding to the exciton splitting energy of the B820 dimer. Significant exciton coherences are also present at higher frequencies, i.e., up to 800 cm−1, which are determined by realizations of the disorder with a large energy gap between the two pigments (which increases the apparent value of the exciton splitting). Although the B820 dimer is a model system, the approach presented here represents a basis for further analyses of more complicated systems, providing a tool for studying the interplay between Electronic and vibrational coherences in disordered photosynthetic antennae and reaction centres.

  • Two-Dimensional Electronic Spectroscopy Reveals Ultrafast Energy Diffusion in Chlorosomes
    Journal of the American Chemical Society, 2012
    Co-Authors: Jakub Dostál, Jakub Pšenčík, Frantisek Vacha, Ramu-nas Augulis, Tomáš Mančal, Donatas Zigmantas
    Abstract:

    Chlorosomes are light-harvesting antennae that enable exceptionally efficient light energy capture and excitation transfer. They are found in certain photosynthetic bacteria, some of which live in extremely low-light environments. In this work, chlorosomes from the green sulfur bacterium Chlorobaculum tepidum were studied by coherent Electronic two-dimensional (2D) Spectroscopy. Previously uncharacterized ultrafast energy transfer dynamics were followed, appearing as evolution of the 2D spectral line-shape during the first 200 fs after excitation. Observed initial energy flow through the chlorosome is well explained by effective exciton diffusion on a sub-100 fs time scale, which assures efficiency and robustness of the process. The ultrafast incoherent diffusion-like behavior of the excitons points to a disordered energy landscape in the chlorosome, which leads to a rapid loss of excitonic coherences between its structural subunits. This disorder prevents observation of excitonic coherences in the experi...

  • two dimensional Electronic Spectroscopy with double modulation lock in detection enhancement of sensitivity and noise resistance
    Optics Express, 2011
    Co-Authors: Ramu-nas Augulis, Donatas Zigmantas
    Abstract:

    In many potential applications of two-dimensional (2D) Electronic Spectroscopy the excitation energies per pulse are strictly limited, while the samples are strongly scattering. We demonstrate a technique, based on double-modulation of incident laser beams with mechanical choppers, which can be implemented in almost any non-collinear four wave mixing scheme including 2D Spectroscopy setup. The technique virtually eliminates artifacts or “ghost” signals in 2D spectra, which arise due to scattering and accumulation of long-lived species. To illustrate the advantages of the technique, we show a comparison of porphyrin J-aggregate 2D spectra obtained with different methods following by discussion.

Tomáš Mančal - One of the best experts on this subject based on the ideXlab platform.

  • Two-Dimensional Electronic Spectroscopy Reveals Ultrafast Energy Diffusion in Chlorosomes
    Journal of the American Chemical Society, 2012
    Co-Authors: Jakub Dostál, Jakub Pšenčík, Frantisek Vacha, Ramu-nas Augulis, Tomáš Mančal, Donatas Zigmantas
    Abstract:

    Chlorosomes are light-harvesting antennae that enable exceptionally efficient light energy capture and excitation transfer. They are found in certain photosynthetic bacteria, some of which live in extremely low-light environments. In this work, chlorosomes from the green sulfur bacterium Chlorobaculum tepidum were studied by coherent Electronic two-dimensional (2D) Spectroscopy. Previously uncharacterized ultrafast energy transfer dynamics were followed, appearing as evolution of the 2D spectral line-shape during the first 200 fs after excitation. Observed initial energy flow through the chlorosome is well explained by effective exciton diffusion on a sub-100 fs time scale, which assures efficiency and robustness of the process. The ultrafast incoherent diffusion-like behavior of the excitons points to a disordered energy landscape in the chlorosome, which leads to a rapid loss of excitonic coherences between its structural subunits. This disorder prevents observation of excitonic coherences in the experi...

  • ultrafast photo induced charge transfer unveiled by two dimensional Electronic Spectroscopy
    Journal of Chemical Physics, 2012
    Co-Authors: Oliver Bixner, Tomáš Mančal, Franz Milota, Vladimir Lukes, Jurgen Hauer, Michael Fischer, Igor Pugliesi, Maximilian Bradler, Walther Schmid, Eberhard Riedle
    Abstract:

    The interaction of exciton and charge transfer (CT) states plays a central role in photo-induced CT processes in chemistry, biology, and physics. In this work, we use a combination of two-dimensional Electronic Spectroscopy (2D-ES), pump-probe measurements, and quantum chemistry to investigate the ultrafast CT dynamics in a lutetium bisphthalocyanine dimer in different oxidation states. It is found that in the anionic form, the combination of strong CT-exciton interaction and Electronic asymmetry induced by a counter-ion enables CT between the two macrocycles of the complex on a 30 fs timescale. Following optical excitation, a chain of electron and hole transfer steps gives rise to characteristic cross-peak dynamics in the Electronic 2D spectra, and we monitor how the excited state charge density ultimately localizes on the macrocycle closest to the counter-ion within 100 fs. A comparison with the dynamics in the radical species further elucidates how CT states modulate the Electronic structure and tune f...

  • ultrafast photo induced charge transfer unveiled by two dimensional Electronic Spectroscopy
    arXiv: Chemical Physics, 2012
    Co-Authors: Oliver Bixner, Tomáš Mančal, Franz Milota, Vladimir Lukes, Jurgen Hauer, Michael Fischer, Igor Pugliesi, Maximilian Bradler, Walther Schmid, Eberhard Riedle
    Abstract:

    The interaction of exciton and charge transfer (CT) states plays a central role in photo-induced CT processes in chemistry, biology and physics. In this work, we use a combination of two-dimensional Electronic Spectroscopy (2D-ES), pump-probe measurements and quantum chemistry to investigate the ultrafast CT dynamics in a lutetium bisphthalocyanine dimer in different oxidation states. It is found that in the anionic form, the combination of strong CT-exciton interaction and Electronic asymmetry induced by a counter-ion enables CT between the two macrocycles of the complex on a 30 fs timescale. Following optical excitation, a chain of electron and hole transfer steps gives rise to characteristic cross-peak dynamics in the Electronic 2D spectra, and we monitor how the excited state charge density ultimately localizes on the macrocycle closest to the counter-ion within 100 fs. A comparison with the dynamics in the radical species further elucidates how CT states modulate the Electronic structure and tune fs-reaction dynamics. Our experiments demonstrate the unique capability of 2D-ES in combination with other methods to decipher ultrafast CT dynamics.

  • Double-quantum two-dimensional Electronic Spectroscopy of a three-level system: Experiments and simulations.
    The Journal of chemical physics, 2010
    Co-Authors: Alexandra Nemeth, Tomáš Mančal, Franz Milota, Tõnu Pullerits, Jaroslaw Sperling, Juergen Hauer, Harald F. Kauffmann, Niklas Christensson
    Abstract:

    Double-quantum coherence two-dimensional (2Q2D) Electronic Spectroscopy is utilized to probe the dynamic fluctuations of Electronic states in a solvated molecule at approximately twice the energy of the ground state bleach transition. The 2Q2D spectrum gives insight into the energetic position and spectral fluctuations (system-bath interaction) of the probed excited states. Combining it with single-quantum two-dimensional (1Q2D) Electronic Spectroscopy enables one to determine the strength of the excited state absorption transition and the relative detuning of Electronic states, as well as the dynamics of the single-quantum coherence. To investigate the correlation of spectral fluctuations in different Electronically excited states, we have carried out experiments on a solvated dye (Rhodamine 6G) with 23 fs pulses centered at the maximum of the linear absorption spectrum. The 2Q2D spectrum reveals three peaks of alternating signs with the major negative peak located at higher frequencies along the emission axis compared to the single positive peak. The 1Q2D spectrum, on the other hand, shows a negative peak stemming from excited state absorption at lower frequencies along the emission axis. Analysis of the signal in the homogeneous limit fails to account for this observation as well as the number of peaks in the 2Q2D spectrum. Employing a three-level model in which all time correlations of the third-order response function are accounted for via second-order cumulant expansion gives good agreement with both the 1Q2D and 2Q2D data. Furthermore, the analysis shows that the fluctuations of the probed Electronic states are highly correlated, reflecting the modulation by a common nuclear bath and similarities in the nature of the Electronic transitions. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3474995]

  • 2D Fourier Transform Electronic Spectroscopy of Photosynthetic Reaction Centers: Mapping coupling in the B band
    15th International Conference on Ultrafast Phenomena, 2006
    Co-Authors: Gregory S. Engel, Tomáš Mančal, Tessa R. Calhoun, Donatas Zigamantas, Hohjai Lee, Graham R Fleming
    Abstract:

    The B800 band of the reaction center complex of Rhodobacter sphaeroides has been probed with two-dimensional Fourier transform Electronic Spectroscopy using 40 fs pulses and evidence for coupling within the band will be presented.