Nature does not rely on long-lived electronic quantum coherence for photosynthetic energy transfer

During the first steps of photosynthesis, the energy of impinging solar photons is transformed into electronic excitation energy of the light-harvesting biomolecular complexes. The subsequent energy transfer to the reaction center is commonly rationalized in terms of excitons moving on a grid of biomolecular chromophores on typical timescales [Formula: see text]100 fs. Today's understanding of the energy transfer includes the fact that the excitons are delocalized over a few neighboring sites, but the role of quantum coherence is considered as irrelevant for the transfer dynamics because it typically decays within a few tens of femtoseconds. This orthodox picture of incoherent energy transfer between clusters of a few pigments sharing delocalized excitons has been challenged by ultrafast optical spectroscopy experiments with the Fenna-Matthews-Olson protein, in which interference oscillatory signals up to 1.5 ps were reported and interpreted as direct evidence of exceptionally long-lived electronic quantum coherence. Here, we show that the optical 2D photon echo spectra of this complex at ambient temperature in aqueous solution do not provide evidence of any long-lived electronic quantum coherence, but confirm the orthodox view of rapidly decaying electronic quantum coherence on a timescale of 60 fs. Our results can be considered as generic and give no hint that electronic quantum coherence plays any biofunctional role in real photoactive biomolecular complexes. Because in this structurally well-defined protein the distances between bacteriochlorophylls are comparable to those of other light-harvesting complexes, we anticipate that this finding is general and directly applies to even larger photoactive biomolecular complexes

Ultrafast dissolution and creation of bonds in IrTe2 induced by photodoping

The observation and control of interweaving spin, charge, orbital, and structural degrees of freedom in materials on ultrafast time scales reveal exotic quantum phenomena and enable new active forms of nanotechnology. Bond- ing is the prime example of the relation between electronic and nuclear degrees of freedom. We report direct evidence illustrating that photoexcitation can be used for ultrafast control of the breaking and recovery of bonds in solids on unprecedented time scales, near the limit for nuclear motions. We describe experimental and theoretical studies of IrTe2 using femtosecond electron diffraction and density functional theory to investigate bonding instability. Ir-Ir dimerization shows an unexpected fast dissociation and recovery due to the filling of the antibonding dxy orbital. Bond length changes of 20% in IrTe2 are achieved by effectively addressing the bonds directly through this relaxation process. These results could pave the way to ultrafast switching between metastable structures by photoinduced manipulation of the relative degree of bonding in this manner

SPATIAL PROPERTIES OF ENERGY TRANSPORT IN THREE DIMENSIONAL DISORDERED SYSTEMS

The picosecond transient grating technique is used to directly measure the excited state energy transport diffusion constant of dye molecules in solution. The use of extremely narrow grating fringe spacings (< 980A) enabled measurement of the excitation's spatial mobility from low concentration (C = 1) where the transport is non-diffusive up to concentrations (C‹≈10) where the transport is essentially diffusive. The results are compared to theortical predictions for the concentration dependence of the diffusive propagation of the excitation

A spatio-spectral polarization analysis of 1 µm-pumped bulk supercontinuum in a cubic crystal (YAG)

We present the first systematic study of the spatio-spectral polarization properties of a supercontinuum generated in a cubic crystal, yttrium–aluminum garnet (YAG), including a full spectral analysis of the white light core and surrounding ring structure. We observe no depolarization of the supercontinuum, and no spatial dependence of polarization ratios for any wavelength. We discuss the discrepancy of YAG’s polarization behavior in the context of well-established results in literature reporting self-induced depolarization in other cubic crystals. © 2018, The Author(s)

Two-dimensional optical correlation spectroscopy applied to liquid/glass dynamics

Correlation spectroscopy was used to study the effects of temperature and phase changes on liquid and glass solvent dynamics. By assessing the eccentricity of the elliptic shape of a 2D optical correlation spectrum the value of the underlying frequency-frequency correlation function can be retrieved through a very simple relationship. This method yielded both intuitive clues and a quantitative measure of the dynamics of the system

Ultrafast intramolecular energy transfer in water

An unexpectedly fast (0.2 ps) intramolecular energy conversion occurring in H2O molecules has been revealed using frequency-resolved mid-infrared pump-probe spectroscopy in the spectral region of the OH-stretching vibration

Anharmonic Bend-Stretch Coupling in Water

Following excitation of the H-O-H bending mode of water molecules in solution the stretching mode region is monitored over its entire width. The anharmonic coupling between the two modes results in a substantial change of the transient stretch absorption that decays with the bend depopulation time. Unlike in the gas phase, the stretch transition shifts to the blue which is a direct consequence of the weakened hydrogen-bond network. © 2006 Optical Society of America

Fixed target matrix for femtosecond time-resolved andﾠin situﾠserial micro-crystallography

We present a crystallography chip enablingﾠin situﾠroom temperature crystallography at microfocus synchrotron beamlines andﾠX-rayﾠfree-electron laser (X-FEL) sources. Compared to otherﾠin situapproaches, we observe extremely low background and highﾠdiffractionﾠdata quality. The chip design is robust and allows fast and efficient loading of thousands of small crystals. The ability to load a large number ofﾠproteinﾠcrystals, at room temperature and with high efficiency, into prescribed positions enables high throughput automated serial crystallography with microfocus synchrotron beamlines. In addition, we demonstrate the application of this chip for femtosecond time-resolved serial crystallography at the Linac Coherent Light Source (LCLS, Menlo Park, California, USA). The chip concept enables multiple images to be acquired from each crystal, allowing differential detection of changes inﾠdiffractionﾠintensities in order to obtain high signal-to-noise and fully exploit the time resolution capabilities of XFELs