103 research outputs found
Exciton delocalization in the antenna of purple bacteria: Exciton spectrum calculations using X-ray data and experimental site inhomogeneity
AbstractElectron absorption and circular dichroism spectra of the peripheral light-harvesting complex (LH2) of photosynthetic purple bacteria were calculated taking into account the real-life spatial arrangement and experimental inhomogeneous broadening of bacteriochlorophyll molecules. It was shown that strong excitonic interactions between 18 bacteriochlorophyll molecules (BChl850) within the circular aggregate of the LH2 complex result in an exciton delocalization over all these pigment molecules. The site inhomogeneity (spectral disorder) practically has no influence on exciton delocalization. The splitting between two lowest exciton levels corresponds to experimentally revealed splitting by hole-burning studies of the LH2 complex
Role of quantum coherence in chromophoric energy transport
The role of quantum coherence and the environment in the dynamics of
excitation energy transfer is not fully understood. In this work, we introduce
the concept of dynamical contributions of various physical processes to the
energy transfer efficiency. We develop two complementary approaches, based on a
Green's function method and energy transfer susceptibilities, and quantify the
importance of the Hamiltonian evolution, phonon-induced decoherence, and
spatial relaxation pathways. We investigate the Fenna-Matthews-Olson protein
complex, where we find a contribution of coherent dynamics of about 10% and of
relaxation of 80%.Comment: 5 pages, 3 figures, included static disorder, correlated environmen
Scalable High-Performance Algorithm for the Simulation of Exciton Dynamics. Application to the Light-Harvesting Complex II in the Presence of Resonant Vibrational Modes
Ab-Initio Calculation of Molecular Aggregation Effects: a Coumarin-343 Case Study
We present time-dependent density functional theory (TDDFT) calculations for
single and dimerized Coumarin-343 molecules in order to investigate the quantum
mechanical effects of chromophore aggregation in extended systems designed to
function as a new generation of sensors and light-harvesting devices. Using the
single-chromophore results, we describe the construction of effective
Hamiltonians to predict the excitonic properties of aggregate systems. We
compare the electronic coupling properties predicted by such effective
Hamiltonians to those obtained from TDDFT calculations of dimers, and to the
coupling predicted by the transition density cube (TDC) method. We determine
the accuracy of the dipole-dipole approximation and TDC with respect to the
separation distance and orientation of the dimers. In particular, we
investigate the effects of including Coulomb coupling terms ignored in the
typical tight-binding effective Hamiltonian. We also examine effects of orbital
relaxation which cannot be captured by either of these models
Two different charge-separation pathways in photosystem II
Charge separation is an essential step in the conversion of solar energy into chemical energy in photosynthesis. To investigate this process, we performed transient absorption experiments at 77 K with various excitation conditions on the isolated Photosystem II reaction center preparations from spinach. The results have been analyzed by global and target analysis and demonstrate that at least two different excited states, (Ch
Linear dichroism and circular dichroism in photosynthesis research
The efficiency of photosynthetic light energy conversion depends largely on the molecular architecture of the photosynthetic membranes. Linear- and circular-dichroism (LD and CD) studies have contributed significantly to our knowledge of the molecular organization of pigment systems at different levels of complexity, in pigment–protein complexes, supercomplexes, and their macroassemblies, as well as in entire membranes and membrane systems. Many examples show that LD and CD data are in good agreement with structural data; hence, these spectroscopic tools serve as the basis for linking the structure of photosynthetic pigment–protein complexes to steady-state and time-resolved spectroscopy. They are also indispensable for identifying conformations and interactions in native environments, and for monitoring reorganizations during photosynthetic functions, and are important in characterizing reconstituted and artificially constructed systems. This educational review explains, in simple terms, the basic physical principles, and theory and practice of LD and CD spectroscopies and of some related quantities in the areas of differential polarization spectroscopy and microscopy
Monte Carlo Simulation of Exciton Bimolecular Annihilation Dynamics in Supramolecular Semiconductor Architectures †
Functional Subsystems and Quantum Redundancy in Photosynthetic Light Harvesting
The Fenna-Matthews-Olson (FMO) antennae complex, responsible for light
harvesting in green sulfur bacteria, consists of three monomers, each with
seven chromophores. Here we show that multiple subsystems of the seven
chromophores can transfer energy from either chromophore 1 or 6 to the reaction
center with an efficiency matching or in many cases exceeding that of the full
seven chromophore system. In the FMO complex these functional subsystems
support multiple quantum pathways for efficient energy transfer that provide a
built-in quantum redundancy. There are many instances of redundancy in nature,
providing reliability and protection, and in photosynthetic light harvesting
this quantum redundancy provides protection against the temporary or permanent
loss of one or more chromophores. The complete characterization of functional
subsystems within the FMO complex offers a detailed map of the energy flow
within the FMO complex, which has potential applications to the design of more
efficient photovoltaic devices
Exciton dynamics in circular aggregates: application to antenna of photosynthetic purple bacteria.
A theoretical model of exciton dynamics in circular molecular aggregates of light-harvesting bacteriochlorophyll of photosynthetic bacteria is proposed. The spectra and anisotropy of photoinduced absorption changes in the femto- and picosecond time domain are under its scope. The excited state of aggregate was treated due to the standard exciton theory, taking into account a pigment inhomogeneity. Dephasing processes via the exciton-phonon interactions were described by means of the Haken-Strobl equation. It was shown that only two exciton levels are dipole-allowed in the case of homogeneous circular aggregate. The pigment inhomogeneity results in the appearance of several weak transitions to higher exciton levels. It was proposed that the minor band (B896) in an absorption spectrum of the B875 complex as well as the similar minor band in spectra of B800-850 complex correspond to electron transition from the ground to the lowest exciton level, whereas the major band corresponds to transition to the higher exciton level. The proposed model shows the subpicosecond decay of anisotropy at the short-wavelength side of absorption band and a high degree of anisotropy at the long-wavelength side, even at high temperatures
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