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Results for “Excitation energy transfer”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Alteration of phycobilisome excitation energy transfer properties in response to attenuations in peripheral electron flow

In Synechocystis sp. PCC 6803 ( S . 6803), two types of phycobilisome (PBS) complexes, CpcG-PBS and CpcL-PBS, function to harvest light energy for photosynthetic reaction centers (RCs), photosystem I (PSI) and photosystem II (PSII). The compositional differences between these two forms of PBS and their specificity for RCs have led to suggestions that they may differ in function. To address this question, we examined how PBS-RC interactions, and the transfer of excitation energy from PBS to RCs, might be adjusted under conditions where electron demand and photon availability are modulated. The CpcG-PBS, CpcL-PBS, and RC complexes were isolated from a S . 6803 strain defective in expression of flavodiiron 1 (oxygen reduction reaction 1, ORR1) grown under varied light regimes. The energy transfer preference from CpcL-PBS to either PSI or PSII was investigated by in vitro crosslinking and 77 K fluorescence emission spectroscopy to assess energy transfer efficiency under photoexcitation. While the results demonstrate that the transfer of excitation energy from CpcL-PBS favors PSI over PSII in WT strains as previously shown, the preference of CpcL-PBS switches from PSI to PSII in ORR1 strains. Surprisingly, this change in preference was reproduced when ORR1 CpcL-PBS was crosslinked with WT RCs, or when WT CpcL-PBS was cross-crosslinked with ORR1 RCs, indicating there are physical modifications to both PBS and RCs that mediate the preference switch. In contrast, the analysis with ORR1 CpcG-PBS shows similar preferences to WT. Additionally, PBS populations in ORR1 shifted to a greater proportion of CpcL-PBS relative to CpcG-PBS. These results demonstrate that under conditions where electron utilization changes, there is a tuning of the excitation energy allocation from CpcL-PBS to RCs to manage the energy distribution for photosynthesis under dynamic flux conditions.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

Excitation Energy Transfer Dynamics from Carotenoid to Bacteriochlorophyll a in the LH2 Complex of Rhodobacter sphaeroides: Insights from Reconstitution Experiments with Carotenoids and B800 Bacteriochlorophyll a

Carotenoids are crucial for photosynthesis, playing key roles in light harvesting and photoprotection. In this study, spheroidene and bacteriochlorophyll a (Bchl a) were reconstituted into the chromatophores of the carotenoidless mutant Rhodobacter sphaeroides R26.1, resulting in the preparation of high-quality LH2 complexes. Global and target analyses of transient absorption data revealed that incorporating B800 Bchl a significantly enhances excitation energy transfer (EET) efficiency from carotenoids to Bchl a. EET predominantly occurs from the carotenoid S2 state, with additional pathways from the S1 state observed in native LH2. Unique relaxation dynamics were identified, including the generation of the carotenoid S* state in reconstituted LH2 with both spheroidene and B800 Bchl a and the formation of the carotenoid T1 state in reconstituted LH2. These findings underscore the critical influence of pigment composition and spatial organization on energy transfer mechanisms. They provide valuable insights into the molecular interplay that governs excitation energy transfer in photosynthetic light-harvesting systems.

Biochemistry & Molecular Biology↗
DOE OSTI2024

Altered excitation energy transfer between phycobilisome and photosystems in the absence of ApcG, a small linker peptide, in Synechocystis sp. PCC 6803, a cyanobacterium

Phycobilisome (PBS) is a large pigment-protein complex in cyanobacteria and red algae responsible for capturing sunlight and transferring its energy to photosystems (PS). Spectroscopic and structural properties of various PBSs have been widely studied, however, the nature of so-called complex-complex interactions between PBS and PSs remains much less explored. In this work, we have investigated the function of a newly identified PBS linker protein, ApcG, some domain of which, together with a loop region (PB-loop in ApcE), is possibly located near the PBS-PS interface. Using Synechocystis sp. PCC 6803, we generated an ApcG deletion mutant and probed its deletion effect on the energetic coupling between PBS and photosystems. Steady-state and time-resolved spectroscopic characterization of the purified ΔApcG-PBS demonstrated that ApcG removal weakly affects the photophysical properties of PBS that the spectroscopic properties of terminal energy emitters are comparable to those of PBS from wild-type. However, analysis of fluorescence decay imaging datasets reveals that ApcG deletion induces disruptions within the allophycocyanin (APC) core, resulting in the emergence (splitting) of two spectrally diverse subgroups with some short-lived APC. Profound spectroscopic changes of the whole ΔApcG mutant cell, however, emerge during state transition, a dynamic process of light scheme adaptation. The mutant cells in State I show a substantial increase in PBS-related fluorescence. On the other hand, global analysis of time-resolved fluorescence demonstrates that in general ApcG deletion does not alter or inhibit state transitions if it is interpreted only in terms of the changes of the PSII and PSI fluorescence emission intensity. Furthermore, the results revealed yet–to–be discovered mechanism of ApcG-docking induced excitation energy transfer regulation within PBS or to Photosystems.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2022

Plasmon-induced excitation energy transfer in silver nanoparticle dimers: A real-time TDDFTB investigation

Here, using real-time quantum dynamics calculations, we perform theoretical investigations of light-induced interactions and electronic excitation transfer in a silver nanoparticle dimer. Real-time time-dependent density functional tight-binding (RT-TDDFTB) calculations provide details of the quantum dynamical processes at an electronic/atomistic level with attosecond resolution. The computational efficiency of RT-TDDFTB allows us to examine electronic dynamics up to picosecond time scales. With time scales varying over six orders of magnitude, we provide insight into interactions between the nanoparticle and laser and between nanoparticles. Our results show that the coupling between nanoparticle monomers is dependent on the separation distance between the nanoparticles in the dimer. As the interparticle distance is varied, the dipole–dipole interactions and electronic excitation transfer mechanisms are markedly different. At large distances (from 50 to 20 Å), the energy transfer from NP1 to NP2 becomes more efficient as the interparticle distance decreases. The total dipole moment of the Ag 14 nanoparticle dimer increases linearly at an interparticle distance of 20 Å and reaches its maximum after 1.2 ps. The electronic excitation transfer is also the most efficient at 20 Å. At short distances, back-transfer effects reduce the ability of the dimer and NP1 to accept energy from the incident electric field. We attribute the distance-dependent features of the nanoparticle dimer to the beating between the laser acting on NP1 and the back transfer from NP2 to NP1.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Excitation energy transfer in proteoliposomes reconstituted with LH2 and RC-LH1 complexes from Rhodobacter sphaeroides

Abstract Light-harvesting 2 (LH2) and reaction-centre light-harvesting 1 (RC-LH1) complexes purified from the photosynthetic bacterium Rhodobacter (Rba.) sphaeroides were reconstituted into proteoliposomes either separately, or together at three different LH2:RC-LH1 ratios, for excitation energy transfer studies. Atomic force microscopy (AFM) was used to investigate the distribution and association of the complexes within the proteoliposome membranes. Absorption and fluorescence emission spectra were similar for LH2 complexes in detergent and liposomes, indicating that reconstitution retains the structural and optical properties of the LH2 complexes. Analysis of fluorescence emission shows that when LH2 forms an extensive series of contacts with other such complexes, fluorescence is quenched by 52.6 ± 1.4%. In mixed proteoliposomes, specific excitation of carotenoids in LH2 donor complexes resulted in emission of fluorescence from acceptor RC-LH1 complexes engineered to assemble with no carotenoids. Extents of energy transfer were measured by fluorescence lifetime microscopy; the 0.72 ± 0.08 ns lifetime in LH2-only membranes decreases to 0.43 ± 0.04 ns with a ratio of 2:1 LH2 to RC-LH1, and to 0.35 ± 0.05 ns for a 1:1 ratio, corresponding to energy transfer efficiencies of 40 ± 14% and 51 ± 18%, respectively. No further improvement is seen with a 0.5:1 LH2 to RC-LH1 ratio. Thus, LH2 and RC-LH1 complexes perform their light harvesting and energy transfer roles when reconstituted into proteoliposomes, providing a way to integrate native, non-native, engineered and de novo designed light-harvesting complexes into functional photosynthetic systems.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

Cyanobacteria dynamically regulate phycobilisome-to-photosystem excitation energy transfer

In cyanobacteria and red algae, the phycobilisome (PBS) absorbs light and transfers its energy to the chlorophylls in photosystems II (PSII) and I (PSI). With the help of target analysis of time-resolved emission spectra measured at room temperature (RT) and at 77 K, we establish a general kinetic scheme for excitation energy transfer (EET) and trapping based upon a PBS-PSII-PSI megacomplex. At RT it is found that in the dark-adapted cells (State II), the terminal emitter of PBS, allophycocyanin APC680, transfers energy to PSII and PSI with equal rates of ≈50 ns −1 , and that spillover from PSII to PSI is present with rate ≈6 ns −1 . At 77 K, upon transition from State I to State II the EET rate from APC680 to PSII is constant, whereas the rate to PSI increases by 67%. This indicates that a structural change in EET distance in the PBS-PSII-PSI megacomplex underlies the state transition.

Science & Technology - Other Topics↗
DOE OSTI2024

Polariton-assisted incoherent to coherent excitation energy transfer between colloidal nanocrystal quantum dots

Here, we explore the dynamics of energy transfer between two nanocrystal quantum dots placed within an optical microcavity. By adjusting the coupling strength between the cavity photon mode and the quantum dots, we have the capacity to fine-tune the effective coupling between the donor and acceptor. Introducing a non-adiabatic parameter, γ, governed by the coupling to the cavity mode, we demonstrate the system’s capability to shift from the overdamped Förster regime (γ $\ll$ 1) to an underdamped coherent regime (γ $\gg$ 1). In the latter regime, characterized by swift energy transfer rates, the dynamics are influenced by decoherence time. To illustrate this, we study the exciton energy transfer dynamics between two closely positioned CdSe/CdS core/shell quantum dots with sizes and separations relevant to experimental conditions. Employing an atomistic approach, we calculate the excitonic level arrangement, exciton–phonon interactions, and transition dipole moments of the quantum dots within the microcavity. These parameters are then utilized to define a model Hamiltonian. Subsequently, we apply a generalized non-Markovian quantum Redfield equation to delineate the dynamics within the polaritonic framework.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Unraveling excitation energy transfer assisted by collective behaviors of vibrations

Abstract We investigate how collective behaviors of vibrations such as cooperativity and interference can enhance energy transfer in a nontrivial way, focusing on an example of a donor–bridge–acceptor trimeric chromophore system coupled to two vibrational degrees of freedom. Employing parameters selected to provide an overall uphill energy transfer from donor to acceptor, we use numerical calculations of dynamics in a coupled exciton–vibration basis, together with perturbation-based analytics and calculation of vibronic spectra, to identify clear spectral features of single- and multi-phonon vibrationally-assisted energy transfer (VAET) dynamics, where the latter include up to six-phonon contributions. We identify signatures of vibrational cooperation and interference that provide enhancement of energy transfer relative to that obtained from VAET with a single vibrational mode. We observe a phononic analogue of two-photon absorption, as well as a novel heteroexcitation mechanism in which a single phonon gives rise to simultaneous excitation of both the trimeric system and the vibrational degrees of freedom. The impacts of vibrations and of the one- and two-phonon VAET processes on the energy transfer are seen to be quite different in the weak and strong site–vibration coupling regimes. In the weak coupling regime, two-phonon processes dominate, whereas in the strong coupling regime up to six-phonon VAET processes can be induced. The VAET features are seen to be enhanced with increasing temperature and site–vibration coupling strength, and are reduced in the presence of dissipation. We analyze the dependence of these phenomena on the explicit form of the chromophore–vibration couplings, with comparison of VAET spectra for local and non-local couplings.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2024

Sub-100-fs energy transfer in coenzyme NADH is a coherent process assisted by a charge-transfer state

Excitation energy transfer (EET) is a key photoinduced process in biological chromophoric assemblies. Here we investigate the factors which can drive EET into efficient ultrafast sub-ps regimes. We demonstrate how a coherent transport of electronic population could facilitate this in water solvated NADH coenzyme and uncover the role of an intermediate dark charge-transfer state. High temporal resolution ultrafast optical spectroscopy gives a 54 ± 11 fs time constant for the EET process. Nonadiabatic quantum dynamical simulations computed through the time-evolution of multidimensional wavepackets suggest that the population transfer is mediated by photoexcited molecular vibrations due to strong coupling between the electronic states. The polar aqueous solvent environment leads to the active participation of a dark charge transfer state, accelerating the vibronically coherent EET process in favorably stacked conformers and solvent cavities. Our work demonstrates how the interplay of structural and environmental factors leads to diverse pathways for the EET process in flexible heterodimers and provides general insights relevant for coherent EET processes in stacked multichromophoric aggregates like DNA strands.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

pH-Dependent Vibrational Dynamics Drives Excited-State Quenching in the Phycobiliprotein Complex PC645

Phycocyanin 645 (PC645) is a closed-form lightharvesting complex found in the lumen of the photosynthetic membrane of cryptophyte algae. These peripheral antenna complexes contain bilin chromophores that absorb sunlight and transfer excitation energy to the core antenna complexes embedded in the thylakoid membrane. The location of cryptophyte antenna complex on the luminal side of the membrane is unusual. During photosynthetic activity, the pH of the lumen drops, by up to two pH units. There is little known about how this pH-change affects the light-harvesting complexes. In this study, we report multiscale simulations using a computationally efficient density functional tight-binding framework to investigate the spectroscopy and excitation energy transfer in the PC645 complex. Complementary experiments were conducted using both steady-state and time-resolved spectroscopic measurements at low, neutral, and high pH values. Our study shows that (de)protonation of specific bilin pigments, namely, the mesobiliverdins (MBVs), modulates the excitation energies, excitonic couplings, and spectral densities. These changes cause excitation transfer rates to increase by up to a factor of two to three, leading to pH-dependent energy transfer pathways in the complex. Using this model, we calculated the pH-dependent fluorescence quantum yield of the system, obtaining quantitative agreement with the experimental results. These computational simulations, supported by experiments, identify MBVs as a more prominent excitation sink than previously realized, and that this role is tuned by pH.

Maity, Sayan [Constructor Univ., Bremen (Germany);↗
DOE OSTI2024

Unraveling Nonequilibrium Generation of Atomic Nitrogen and Hydrogen in Plasma-Aided Ammonia Synthesis

In this study, nonequilibrium generation of atomic nitrogen and hydrogen governing ammonia production both in the gas phase and on the catalyst surface is critical to plasma-aided ammonia synthesis. Here, this work studies the nonequilibrium generation of atomic nitrogen and hydrogen with a focus on the kinetic role of vibrational energy transfer of hydrogen molecules in plasma-aided ammonia synthesis. By combining two-photon absorption laser-induced fluorescence measurements and plasma kinetic modeling, we found that plasma not only generates ammonia but also produces critical H, N, and NH radicals via both electron impact and vibrational energy transfer excitations. The vibrational energy transfer from the excited hydrogen H 2 (v = 1) to higher vibrational levels H 2 (v = 2–3) via the V–V exchange (H 2 (v)–H 2 (v)) and V–V' exchange (N 2 (v)–H 2 (v)) significantly enhances the H and NH production and then promotes the coupling between N and NH for ammonia synthesis both in the gas phase and on the catalyst surface.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Probing the Effects of Electronic–Vibrational Resonance on the Rate of Excited-State Energy Transfer in Bacteriochlorin Dyads

Here, the impact of vibrational–electronic resonances on the rate of excited-state energy transfer is examined in a set of bacteriochlorin dyads that employ the same phenylethyne linker. The donor/acceptor excited-state energy gap is tuned from ~200 to ~1100 cm –1 using peripheral substituents on the donor and acceptor bacteriochlorin macrocycles. Ultrafast energy transfer is observed with rate constants of (0.3 ps) –1 to (1.7 ps) –1 , which agree with those predicted by Förster theory to within a factor of 2. Furthermore, the measured rates follow a trend-line with only small deviations that do not correlate with the density of vibrations at the donor/acceptor excited-state energy gap. Thus, if vibrational–electronic resonances occur in any of these dyads, which seems likely, the impact on the rate of energy transfer is small.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗