A little coherence in photosynthetic light harvesting

How could quantum mechanics possibly be important in biology We will discuss this question in the light of recent experiments that suggest that quantum mechanics - or at least coherence - is at play after photosynthesis is initiated by light. First, we give a brief description of light harvesting in photosynthesis. We follow this with an introduction to two-dimensional electronic spectroscopy, in which we demonstrate how this spectroscopic technique can be used to indicate coherent contributions to energy transfer dynamics. As a final point, we focus on the possible role that coherence may play in photosynthetic biological systems. © 2013 The Author(s) 2013. Published by Oxford University Press on behalf of the American Institute of Biological Sciences. All rights reserved. For Permissions, please e-mail: [email protected]

Southend-on-Sea Borough local plan first alteration Proposed further modifications and reasons for proposing them; minor changes to: detailed guidance for Marine Parade, Leigh-on-Sea; gypsy caravan sites

SIGLEAvailable from British Library Document Supply Centre-DSC:OP-LG/8674 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

The photophysics of cryptophyte light-harvesting

Recent studies of the optical properties and the critical role of phycobiliproteins in the absorption of green light for photosynthesis in cryptophyte algae (Rhodomonas CS24 and Chroomonas CCMP270) are reviewed. Investigations of two different isolated proteins, phycoerythrin 545 (PE545) and phycocyanin 645 (PC645), whose crystal structures are known to 0.97 and 1.4 Å resolution respectively, are described. Steady-state spectroscopic measurements, including polarization anisotropy and circular dichroism, are used in combination with ultrafast transient grating and transient absorption techniques to elucidate a detailed picture of resonance energy transfer within the light-harvesting proteins. Quantum chemical calculations are employed to estimate phycobilin excited states, and generate transition density cubes which are used to calculate accurately the electronic coupling between the chromophores in PE545 and PC645. Energy transfer dynamics are examined using the generalized Förster theory. Kinetic models for energy transfer dynamics in both proteins are presented for comparison. Investigations of energy transfer from phycoerythrin 545 to chlorophyll-containing light harvesting complexes and photosystems in the intact algae Rhodomonas CS24 and Chroomonas CCMP270 are also reported. © 2006 Elsevier B.V. All rights reserved

Upconversion photoluminescence of CdS nanocrystals in polymeric film

10.1063/1.2960536Journal of Applied Physics1042-JAPI

Two-dimensional electronic spectroscopy using rotating optical flats

In two-dimensional electronic spectroscopy (2DES), precise control of the arrival time of ultrashort laser pulses is critical to correlating the molecular states that are accessed in the experiment. In this work, we demonstrate a 2D electronic spectrometer design with an interferometric phase stability of ∼λ/250 at 600 nm. First, we present a new method for controlling pulse delay times based on transmission through pairs of optical flats rotated perpendicular to the beam propagation direction. Second, the calibration methods required to achieve adequate timing precision are also reported. Compared to existing designs using translating wedges, the rotating optical flats can achieve equivalent optical delay with a shorter path length in glass, reducing errors due to spectral dispersion of the broadband laser pulses used in 2DES. Our approach presents a simple, low-cost technique for multidimensional optical spectroscopy that is capable of resolving complex light-induced dynamics.Patrick C. Tapping, Yin Song, Yoichi Kobayashi, Gregory D. Scholes, and Tak W. Ke

Light-harvesting antennae for polymer solar cells

The authors demonstrate the incorporation of an artificial, extrinsic antenna into organic, conjugated polymer layers. This can lead to the independent optimization of spectral and spatial cross section for light absorption in organic solar devices. They report studies of three antenna layers, anthracene, 9,10-dichloroanthracene, and 9,10-diphenylanthracene, that are spin coated onto a poly[2-methoxy,5-(2methyl hexoxy)-1,4-phenylenevinylene] thin film. © 2006 American Institute of Physics

Direct observation of three-photon resonance in water-soluble ZnS quantum dots

10.1063/1.2906904Applied Physics Letters9213-APPL

Energy flow in the cryptophyte PE545 antenna is directed by bilin pigment conformation

Structure-based calculations are combined with quantitative modeling of spectra and energy transfer dynamics to detemine the energy transfer scheme of the PE545 principal light-harvesting antenna of the cryptomonad Rhodomonas CS24. We use a recently developed quantum-mechanics/molecular mechanics (QM/MM) method that allows us to account for pigment-protein interactions at atomic detail in site energies, transition dipole moments, and electronic couplings. In addition, conformational flexibility of the pigment-protein complex is accounted for through molecular dynamics (MD) simulations. We find that conformational disorder largely smoothes the large energetic differences predicted from the crystal structure between the pseudosymmetric pairs PE