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Femtosecond transient absorption measurements were performed on native and a series of reconstituted LH2 complexes from Rhodopseudomonas acidophila 10050 at room temperature. The reconstituted complexes contain chemically modified tetrapyrrole pigments in place of the native bacteriochlorophyll a-B800 molecules. The spectral characteristics of the modified pigments vary significantly, such tha
Energy transfer within the peripheral light-harvesting antenna of the purple bacteria Rhodobacter sphaeroides and Rhodopseudomonas palustris was studied by one- and two-color pump-probe absorption spectroscopy with approximately 100-fs tunable pulses at room temperature and at 77 K. The energy transfer from B800 to B850 occurs with a time constant of 0.7 +/- 0.05 ps at room temperature and 1.8 +/-
Fluorescence line-narrowing measurements at low temperature were performed on the Fenna-MatthewsOlson complex of Prosthecochloris aestuarii. Superimposed on the phonon wing, several vibronic bands could be observed. By use of these data, the temperature dependence of the lowest-energy absorption band was modeled based on the linear harmonic Franck-Condon approximation. The overall Huang-Rhys facto
Great progress in the study of structure and dynamics of photosynthetic light-harvesting pigment-protein complexes has recently resulted in detailed understanding of the light-harvesting and light-conversion processes of photosynthesis. We review and discuss recent results on the elementary excitation transfer dynamics of the purple bacterial LH2 peripheral complex. When combining the information
Energy transfer within various LH2 antenna complexes of the photosynthetic purple bacteria Rhodobacter sphaeroides and Rhodopseudomonas acidophila has been studied at 77 K using tunable femtosecond and subpicosecond infrared pulses. The complexes examined include the wild-type B800-850 as well as three different specifically mutated complexes. The site-directed mutant strains were altered at posit
The light-harvesting apparatus of the photosynthetic bacterium Rhodobacter sphaeroides is composed of a peripheral LH2 complex which directs excitation energy to the LH1/reaction center core. The puf BA genes encoding the LH1 polypeptides have been deleted, producing a photosynthetically-competent strain which contains LH2 and reaction centers. Time-resolved absorption and fluorescence measurement
Anisotropy and isotropic transient absorption decays of a polythiophene derivative in dilute solution have been measured and compared to calculated decays on Monte Carlo simulated polymer chains to obtain knowledge about the geometrical conformation of the polymer. The polymer chain conformations are generated by a partially correlated self-avoiding random walk. Excitation migration along the isol
In this article we briefly review the molecular exciton theory and apply it to photosynthetic light harvesting systems. We derive expressions for exciton relaxation rates using perturbation theory in Hibert space representation and show how the Förster equation can be obtained from a general relaxation rate expression in case of well localized excitons. A detailed analysis of the exciton level str
We have studied excitation energy transfer in the photosynthetic antenna systems LH1 and LH2 of purple bacteria. Femtosecond pump−probe experiments are combined with computer simulations using the recently established crystal structure of these systems to assess the nature of excitation motion. We have measured the transient absorption kinetics and spectra of the LH1 and LH2 complexes in the
The excited state decay kinetics of chromatophores of the purple photosynthetic bacterium Rhodospirillum rubrum have been recorded at 77 K using picosecond absorption difference spectroscopy under strict annihilation free conditions. The kinetics are shown to be strongly detection wavelength dependent. A simultaneous kinetic modeling of these experiments together with earlier fluorescence kinetics
Using two-color pump−probe femtosecond spectroscopy, the temperature dependence of the energy transfer rate within the peripheral light-harvesting antenna (LH2) of the photosynthetic bacterium Rhodobacter sphaeroides has been measured. The energy transfer time from B800 to B850 is determined to be 0.7, 1.2, and 1.5 ps at 300, 77, and 4.2 K, respectively. These data, combined with earlier resu
Developing novel organic photovoltaic materials for organic solar cells (OSCs) requires precise characterization of their charge transfer states to optimize the photoinduced charge transfer mechanisms within the photoactive layer. The microscopic photoelectric properties of the S-shaped (DYA-I-S) and O-shaped (DYA-I-O) conformations of dimeric small molecule acceptors (DSMAs) are analyzed through
Picosecond spectrally resolved fluorescence kinetics measurements, together with model simulations of the obtained data, based on coupled rate equations, have been employed to determine the rates and the pathways of heterogeneous excitation transfer in Rhodobacter sphaeroides and Chromatium minutissimum. The presence of a directed excitation flow from the short-wavelength bacteriochlorophyll
The intensity dependence of picosecond kinetics in the light-harvesting antenna of the photosynthetic bacterium Rhodospirillum rubrum is studied at 77 K. By changing either the average excitation intensity or the pulse intensity we have been able to discriminate singlet-singlet and singlet- triplet annihilation. It is shown that the kinetics of both annihilation types are well characterized by the
Epitaxial shell is vital for enhancing the optoelectronic performance of semiconductor quantum dots (QDs), especially for the wide bandgap blue QDs, yet the shell crystal structure's impact on thermal stability and photophysical behavior remains unexplored. It is reported that the ligand-directed synthesis of ZnS shells with zinc blende (ZB) or wurtzite (WZ) structure on blue WZ CdZnS cores, where
Artificial intelligence (AI) and machine learning (ML) are rapidly permeating nearly every aspect of modern life, frompersonal devices and autonomous systems to industrial automation and environmental monitoring. The growing demandfor intelligence at the network edge is reshaping how computing hardware is conceived and built. Edge AI platforms areexpected to deliver high throughput within tight en
With the growing need to process large volumes of data, edge computing near data collection sources has become increasingly important. However, the resource constraints of edge devices require more efficient data processing techniques. Near-memory computing (NMC) presents an efficient solution, especially for data-intensive applications, by enabling processing that is both energy-efficient and har
The random k-SAT model is one of the most important and well-studied distributions over k-SAT instances. It is closely connected to statistical physics and is a benchmark for satisfiability algorithms. We show that when k=Θ(log n) , any Cutting Planes refutation for random k-SAT requires exponential length in the regime where the number of clauses guarantees that the formula is unsatisfiable with
Connections between proof complexity and circuit complexity have become major tools for obtaining lower bounds in both areas. These connections – which take the form of interpolation theorems and query-to-communication lifting theorems – translate efficient proofs into small circuits, and vice versa, allowing tools from one area to be applied to the other. Recently, the theory of TFNP has emerged
