Ozone priming enhanced low temperature tolerance of wheat (Triticum aestivum L.) based on physiological, biochemical and transcriptional analyses.

Low temperature significantly inhibits the plant growth in wheat (Triticum aestivum L.), prompting the exploration of effective strategies to mitigate low temperature stress. Several priming methods enhance low temperature stress tolerant, however, the role of ozone priming remains unclear in wheat. Here we found ozone priming alleviated low temperature stress in wheat. Transcriptome analysis showed that ozone priming positively modulated 'photosynthesis-antenna proteins' pathway in wheat under low temperature. Which was confirmed by the results of the ozone-primed plants had higher trapped energy flux and electron transport flux per reaction, and less damage to chloroplasts than non-primed plants under low temperature. Ozone priming also mitigated the overstimulation of glutathione metabolism and induced the accumulation of total ascorbic acid and glutathione, maintained redox homeostasis in wheat under low temperature. Moreover, gene expressions and enzyme activities in glycolysis pathways were upregulated in ozone priming comparing with non-priming after the low temperature stress. Furthermore, exogenous antibiotics significantly increased low temperature tolerance, which further proved that the inhibition of ribosome biogenesis by ozone priming was involved in low temperature tolerance in wheat. In conclusion, ozone priming enhanced wheat low temperature tolerance through promoting light-harvesting capacity, redox homeostasis, and carbohydrate metabolism, as well as inhibiting ribosome biogenesis.

Integrated transcriptomic and metabolomic analysis reveals the effects and potential mechanism of hydrogen peroxide on pigment metabolism in postharvest broccoli.

To understand the effects and related potential mechanism of H2O2 on pigment metabolism in postharvest broccoli, an integrated analysis of transcriptome and metabolome was performed. Results suggested that 65 differentially expressed genes and 26 differentially accumulated metabolites involved in chlorophyll, carotenoid, and flavonoid metabolism were identified. H2O2 treatment delayed the decrease of chlorophyll content by upregulating the expressions of chlorophyll synthetic genes, thylakoid synthetic genes, and 15 light-harvesting complex genes compared with the control and diphenylene iodonium treatments. H2O2 treatment decreased the accumulation of 11 flavonoids and 5 flavonols by downregulating the flavonoid synthetic genes. In addition, H2O2 treatment promoted carotenoid biosynthesis to eliminate reactive oxygen species in thylakoids, thereby protecting chlorophyll molecules from degradation. The inhibition of flavonoids and flavonols accumulation and chlorophyll decrease was the crucial reason for the delayed yellowing in H2O2 treatment. This study provides a new method and theoretical support for delaying the yellowing process in postharvest broccoli.

A quick comparison model on optimizing the efficiency of photovoltaic panels in collecting solar radiation.

Few scholars study light efficiency of solar-cell arrays in theory, while it is difficult to experimentally determine the maximum capacity of a photovoltaic panel to collect solar radiation. This paper proposes a solar energy comparison model (SECM), considering the sunshine duration changes every day to optimize the solar radiation collection model in an ideal state for a whole year, which is easy to use, and can quickly obtain the optimal tilt angle of photovoltaic panels and the solar radiation collecting efficiency enhancement of intelligent light tracking photovoltaic panels. The results show that the sunshine duration is an important factor affecting the solar radiation received by photovoltaic panels. In regions from 66°34'N to 66°34'S, intelligent light tracking photovoltaic panels can increase the collected solar radiation by at least 63.55%, up to 122.51% compared to stationary photovoltaic panels during the effective light time, which is much higher than what most people generally thought. And the advantage of intelligent light tracking photovoltaic panels is more obvious in high latitudes, with a longer and more variable sunshine duration. These findings provide a theoretical basis for the solar radiation collection and photovoltaic panels.

Spectral modulation of B850 bacteriochlorophyll a in light-harvesting complex 2 from purple photosynthetic bacterium Thermochromatium tepidum by detergents and calcium ions.

Spectral variations of light-harvesting (LH) proteins of purple photosynthetic bacteria provide insight into the molecular mechanisms underlying spectral tuning of circular bacteriochlorophyll (BChl) arrays, which play crucial roles in photoenergy conversion in these organisms. Here we investigate spectral changes of the Qy band of B850 BChl a in LH2 protein from purple sulfur bacterium Thermochromatium tepidum (tepidum-LH2) by detergents and Ca2+. The tepidum-LH2 solubilized with lauryl dimethylamine N-oxide and n-octyl-ß-D-glucoside (LH2LDAO and LH2OG, respectively) exhibited blue-shift of the B850 Qy band with hypochromism compared with the tepidum-LH2 solubilized with n-dodecyl-ß-D-maltoside (LH2DDM), resulting in the LH3-like spectral features. Resonance Raman spectroscopy indicated that this blue-shift was ascribable to the loss of hydrogen-bonding between the C3-acetyl group in B850 BChl a and the LH2 polypeptides. Ca2+ produced red-shift of the B850 Qy band in LH2LDAO by forming hydrogen-bond for the C3-acetyl group in B850 BChl a, probably due to a change in the microenvironmental structure around B850. Ca2+-induced red-shift was also observed in LH2OG although the B850 acetyl group is still free from hydrogen-bonding. Therefore, the Ca2+-induced B850 red-shift in LH2OG would originate from an electrostatic effect of Ca2+. The current results suggest that the B850 Qy band in tepidum-LH2 is primarily tuned by two mechanisms, namely the hydrogen-bonding of the B850 acetyl group and the electrostatic effect.

Molecular events accompanying aggregation-induced energy quenching in fucoxanthin-chlorophyll proteins.

In high light, the antenna system in oxygenic photosynthetic organisms switches to a photoprotective mode, dissipating excess energy in a process called non-photochemical quenching (NPQ). Diatoms exhibit very efficient NPQ, accompanied by a xanthophyll cycle in which diadinoxanthin is de-epoxidized into diatoxanthin. Diatoms accumulate pigments from this cycle in high light, and exhibit faster and more pronounced NPQ. The mechanisms underlying NPQ in diatoms remain unclear, but it can be mimicked by aggregation of their isolated light-harvesting complexes, FCP (fucoxanthin chlorophyll-a/c protein). We assess this model system by resonance Raman measurements of two peripheral FCPs, trimeric FCPa and nonameric FCPb, isolated from high- and low-light-adapted cells (LL,HL). Quenching is associated with a reorganisation of these proteins, affecting the conformation of their bound carotenoids, and in a manner which is highly dependent on the protein considered. FCPa from LL diatoms exhibits significant changes in diadinoxanthin structure, together with a smaller conformational change of at least one fucoxanthin. For these LL-FCPa, quenching is associated with consecutive events, displaying distinct spectral signatures, and its amplitude correlates with the planarity of the diadinoxanthin structure. HL-FCPa aggregation is associated with a change in planarity of a 515-nm-absorbing fucoxanthin, and, to a lesser extent, of diadinoxanthin. Finally, in FCPb, a blue-absorbing fucoxanthin is primarily affected. FCPs thus possess a plastic structure, undergoing several conformational changes upon aggregation, dependent upon their precise composition and structure. NPQ in diatoms may therefore arise from a combination of structural changes, dependent on the environment the cells are adapted to.

Martini 3 Coarse-Grained Model for the Cofactors Involved in Photosynthesis.

As a critical step in advancing the simulation of photosynthetic complexes, we present the Martini 3 coarse-grained (CG) models of key cofactors associated with light harvesting (LHCII) proteins and the photosystem II (PSII) core complex. Our work focuses on the parametrization of beta-carotene, plastoquinone/quinol, violaxanthin, lutein, neoxanthin, chlorophyll A, chlorophyll B, and heme. We derived the CG parameters to match the all-atom reference simulations, while structural and thermodynamic properties of the cofactors were compared to experimental values when available. To further assess the reliability of the parameterization, we tested the behavior of these cofactors within their physiological environments, specifically in a lipid bilayer and bound to photosynthetic complexes. The results demonstrate that our CG models maintain the essential features required for realistic simulations. This work lays the groundwork for detailed simulations of the PSII-LHCII super-complex, providing a robust parameter set for future studies.

Tunable multicolor supramolecular assemblies based on phosphorescence cascade energy transfer for photocatalytic organic conversion and anti-counterfeiting.

Making full use of the captured energy by phosphorescence light-harvesting systems (PLHSs) and the tunable photoluminescence in energy transfer process to realize the multiple applications is still the challenge of PLHSs research. In this study, we have successfully constructed a highly effective PLHS with tunable multicolor luminescence and efficient conversion of photosensitizer types, which can further be used in photocatalytic organic conversion, information anti-counterfeiting and storage. The supramolecular polymer of BDBP-CB[8], which is generated by cucurbit[8]uril (CB[8]) and 4-(4-bromophenyl)-pyridine derivative (BDBP), realizes a phosphorescence emission and a change in luminescence color. Notably, white light emission was achieved and the logic gate systems were constructed utilizing the application of adjustable luminescence color. More interestingly, PLHS can be constructed by employing BDBP-CB[8] as energy donors, Sulforhodamine 101 (SR101) and Cyanine5 (Cy5) as energy acceptors, which results in a remarkably tunable multicolor photoluminescence to achieve the information storage. Furthermore, we have also found that BDBP-CB[8] can serve as type II photosensitizer for the effective production of singlet oxygen (1O2) during the photooxidation process of styrene in aqueous environments, attaining a remarkable output rate reaching as high as 89 %. Particularly, compared with 1O2 produced by type II photosensitizer BDBP-CB[8], the construction of PLHS can effectively convert type II photosensitizer to type I photosensitizer and efficiently generate superoxide anion radical (O2•-), which can be used for photocatalytic cross-dehydrogenative coupling (CDC) reaction in the aqueous solution with a yield of 90 %. Thus, we have created a PLHS that not only achieves tunable multicolor emission for information anti-counterfeiting and storage, but also realizes the conversion of reactive oxygen species (ROS) for different types photocatalytic oxidation reactions.

Helicene Covalent Organic Frameworks for Robust Light Harvesting and Efficient Energy Transfers.

Helicenes represent a class of fascinating π compounds with fused yet folded backbones. Despite their broad structural diversity, harnessing helicenes to develop well-defined materials is still a formidable challenge. Here we report the synthesis of crystalline porous helicene materials by exploring helicenes to synthesize covalent 2D lattices and layered π frameworks. Topology-directed polymerization of [6]helicenes and porphyrin creates 2D covalent networks with alternate helicene-porphyrin alignment along the x and y directions at a 1.5-nm interval and develops [6]helicene frameworks through reversed anti-AA stack along the z direction to form segregated [6]helicene and porphyrin columnar π arrays. Notably, this π configuration enables the frameworks to be highly red luminescent with benchmark quantum yields. The [6]helicene frameworks trigger effieicnt intra-framework singlet-to-singlet state energy transfer from [6]helicene to porphyrin and facilitate intermolecular triplet-to-triplet state energy transfer from frameworks to molecular oxygen to produce reactive oxygen species, harvesting a wide range of photons from ultraviolet to near-infrared regions for light emitting and photo-to-chemical conversion. This study introduces a new family of extended frameworks, laying the groundwork for exploring well-defined helicene materials with unprecedented structures and functions.

Structural and spectroscopic insights into fucoxanthin chlorophyll a/c-binding proteins of diatoms in diverse oligomeric states.

Diatoms, a group of prevalent marine algae, contribute significantly to global primary productivity. Their substantial biomass is linked to enhanced absorption of blue-green light underwater, facilitated by fucoxanthin chlorophyll (Chl) a/c-binding proteins (FCPs), which exhibit oligomeric diversity across diatom species. Using mild clear native PAGE analysis of solubilized thylakoid membranes, we displayed monomeric, dimeric, trimeric, tetrameric, and pentameric FCPs in diatoms. Mass spectrometry analysis revealed that each oligomeric FCP has a specific protein composition, and together they constitute a large Lhcf family of FCP antennas. In addition, we resolved the structures of the Thalassiosira pseudonana FCP (Tp-FCP) homotrimer and the Chaetoceros gracilis FCP (Cg-FCP) pentamer by cryoelectron microscopy at 2.73-Å and 2.65-Å resolution, respectively. The distinct pigment compositions and organizations of various oligomeric FCPs affect their blue-green light-harvesting, excitation energy transfer pathways. Compared with dimeric and trimeric FCPs, the Cg-FCP tetramer and Cg-FCP pentamer exhibit stronger absorption by Chl c, redshifted and broader Chl a fluorescence emission, and more robust circular dichroism signals originating from Chl a-carotenoid dimers. These spectroscopic characteristics indicate that Chl a molecules in the Cg-FCP tetramer and Cg-FCP pentamer are more heterogeneous than in both dimers and the Tp-FCP trimer. The structural and spectroscopic insights provided by this study contribute to a better understanding of the mechanisms that empower diatoms to adapt to fluctuating light environments.

Geometry, reactivity descriptors, light harvesting efficiency, molecular radii, diffusion coefficient, and oxidation potential of RE(I)(CO)3Cl(TPA-2, 2'-bipyridine) in DSSC application: DFT/TDDFT study.

Dye-sensitized solar cells (DSSCs) are an excellent alternative solar cell technology that is cost-effective and environmentally friendly. The geometry, reactivity descriptors, light-harvesting efficiency, molecular radii, diffusion coefficient, and excited oxidation state potential of the proposed complex were investigated. The calculations in this study were performed using DFT/TDDFT method with B3LYP functional employed on the Gaussian 09 software package. The calculations were used the 6-311 + + G(d, p) basis set for the C, H, N, O, Cl atoms and the LANL2DZ basis set for the Re atom, with the B3LYP functional.. The balance of hole and electron in this complex has increased the efficiency and lifetime of DSSCs for photovoltaic cell applications. The investigated compound shows that the addition of the TPA substituent marginally changes the geometric structures of the 2, 2'-bipyridine ligand in the T1 state. As EDsubstituents were added to the compound, the energy gap widened and moved from ELUMO (- 2.904 eV) (substituted TPA) to ELUMO (- 3.122 eV) (unsubstituted). In the studying of solvent affects; when the polarity of the solvent decreases, red shifts appears in the lowest energy an absorption and emission band. Good light-harvesting efficiency, molecular radii, diffusion coefficient, excited state oxidation potential, emission quantum yield, and DSSC reorganization energy, the complex is well suited for use as an emitter in dye-sensitized solar cells. Among the investigated complexes mentioned in literature, the proposed complex was a suitable candidate for phosphorescent DSSC.

Nanotechnology for the enhancement of algal cultivation and bioprocessing: Bridging gaps and unlocking potential.

Algae cultivation and bioprocessing are important due to algae's potential to effectively tackle crucial environmental challenges like climate change, soil and water pollution, energy security, and food scarcity. To realize these benefits high algal biomass production and valuable compound extraction are necessary. Nanotechnology can significantly improve algal cultivation through enhanced nutrient uptake, catalysis, CO2 utilization, real-time monitoring, cost-effective harvesting, etc. Synthetic nanoparticles are extensively used due to ease of manufacturing and targeted application. Nonetheless, there is a growing interest in transitioning to environmentally friendly options like natural and 'green' nanoparticles which are produced from renewable/biological sources by using eco-friendly solvents. Presently, natural, and 'green' nanoparticles are predominantly utilized in algal harvesting, with limited application in other areas, the reasons for which remain unclear. This review aims to critically evaluate research on nanotechnology-based algae system enhancement, identify research gaps and propose solutions using natural and 'green' nanoparticles for a sustainable future.

Tailoring Light-Harvesting in Zn-Porphyrin and Carbon Fullerene based Donor-Acceptor Complex through Ethynyl-Extended Donor π-Conjugation.

Organic photovoltaic efficiency though currently limited for practical applications, can be improved by means of various molecular-level modifications. Herein the role of extended donor π ${\pi }$ -conjugation through ethynyl-bridged meso-phenyl/pyridyl on the photoinduced charge-transfer kinetics is studied in noncovalently bound Zn-Porphyrin and carbon-fullerene based donor-acceptor complex using time-dependent optimally tuned range-separated hybrid combined with the kinetic rate theory in polar solvent. Noncovalent dispersive interaction is identified to primarily govern the complex stability. Ethynyl-extended π ${\pi }$ -conjugation results in red-shifted donor-localized Q-band with substantially increased dipole oscillator strength and smaller exciton binding energy, suggesting greater light-harvesting efficiency. However, the low-lying charge-transfer state below to the Q-band is relatively less affected by the ethynyl-extended π ${\pi }$ -conjugation, yielding reduced driving forces for the charge-transfer. Detailed kinetics analysis reveals similar order of charge-transfer rate constants (~1012 s-1) for all donor-acceptor composites studied. Importantly, enhanced light-absorption, smaller exciton binding energy and similar charge-transfer rates together with reduced charge-recombination make these complexes suitable for efficient photoinduced charge-separation. These findings will be helpful to molecularly design the advanced organic donor-acceptor blends for energy efficient photovoltaic applications.

Enhancing Efficiency of Dye Sensitized Solar Cells by Coinage Metal Doping of Cyanidin-Silver Trimer Hybrids at TiO2 Support Based on Theoretical Study.

Identification of a natural-based sensitizer with optimal stability and efficiency for dye-sensitized solar cell (DSSC) application remains a challenging task. Previously, we proposed a new class of sensitizers based on bio-nano hybrids. These systems composed of natural cyanidin dyes interacting with silver nanoclusters (NCs) have demonstrated enhanced opto-electronic and photovoltaic properties. In this study, we explore the doping of silver nanocluster within a cyanidin-Ag3 hybrid employing Density Functional Theory (DFT) and its time-dependent counterpart (TDDFT). Specifically, we investigate the influence of coinage metal atoms (Au and Cu) on the properties of the cyanidin-Ag3 system. Our findings suggest that cyanidin-Ag2Au and cyanidin-AgAuCu emerge as the most promising candidates for improved light harvesting efficiency, increased two-photon absorption, and strong coupling to the TiO2 surface. These theoretical predictions suggest the viability of replacing larger silver NCs with heterometallic trimers such as Ag2Au or AgAuCu, presenting new avenues for utilizing bio-nano hybrids at the surface for DSSC application.

Characterization of the far-red light absorbing light-harvesting chlorophyll a/b binding complex, a derivative of the distinctive Lhca gene family in green algae.

Prasiola crispa, an aerial green alga, exhibits remarkable adaptability to the extreme conditions of Antarctica by forming layered colonies capable of utilizing far-red light for photosynthesis. Despite a recent report on the structure of P. crispa's unique light-harvesting chlorophyll (Chl)-binding protein complex (Pc-frLHC), which facilitates far-red light absorption and uphill excitation energy transfer to photosystem II, the specific genes encoding the subunits of Pc-frLHC have not yet been identified. Here, we report a draft genome sequence of P. crispa strain 4113, originally isolated from soil samples on Ongul Island, Antarctica. We obtained a 92 Mbp sequence distributed in 1,045 scaffolds comprising 10,244 genes, reflecting 87.1% of the core eukaryotic gene set. Notably, 26 genes associated with the light-harvesting Chl a/b binding complex (LHC) were identified, including four Pc-frLHC genes, with similarity to a noncanonical Lhca gene with four transmembrane helices, such as Ot_Lhca6 in Ostreococcus tauri and Cr_LHCA2 in Chlamydomonas reinhardtii. A comparative analysis revealed that Pc-frLHC shares homology with certain Lhca genes found in Coccomyxa and Trebouxia species. This similarity indicates that Pc-frLHC has evolved from an ancestral Lhca gene with four transmembrane helices and branched out within the Trebouxiaceae family. Furthermore, RNA-seq analysis conducted during the initiation of Pc-frLHC gene induction under red light illumination indicated that Pc-frLHC genes were induced independently from other genes associated with photosystems or LHCs. Instead, the genes of transcription factors, helicases, chaperones, heat shock proteins, and components of blue light receptors were identified to coexpress with Pc-frLHC. Those kinds of information could provide insights into the expression mechanisms of Pc-frLHC and its evolutional development.

Chemical Protein Crosslinking-Coupled Mass Spectrometry Reveals Interaction of LHCI with LHCII and LHCSR3 in Chlamydomonas reinhardtii.

The photosystem I (PSI) of the green alga Chlamydomonas reinhardtii associates with 10 light-harvesting proteins (LHCIs) to form the PSI-LHCI complex. In the context of state transitions, two LHCII trimers bind to the PSAL, PSAH and PSAO side of PSI to produce the PSI-LHCI-LHCII complex. In this work, we took advantage of chemical crosslinking of proteins in conjunction with mass spectrometry to identify protein-protein interactions between the light-harvesting proteins of PSI and PSII. We detected crosslinks suggesting the binding of LHCBM proteins to the LHCA1-PSAG side of PSI as well as protein-protein interactions of LHCSR3 with LHCA5 and LHCA3. Our data indicate that the binding of LHCII to PSI is more versatile than anticipated and imply that LHCSR3 might be involved in the regulation of excitation energy transfer to the PSI core via LHCA5/LHCA3.

A Comprehensive Study of Light Quality Acclimation in Synechocystis Sp. PCC 6803.

Cyanobacteria play a key role in primary production in both oceans and fresh waters and hold great potential for sustainable production of a large number of commodities. During their life, cyanobacteria cells need to acclimate to a multitude of challenges, including shifts in intensity and quality of incident light. Despite our increasing understanding of metabolic regulation under various light regimes, detailed insight into fitness advantages and limitations under shifting light quality remains underexplored. Here, we study photo-physiological acclimation in the cyanobacterium Synechocystis sp. PCC 6803 throughout the photosynthetically active radiation (PAR) range. Using light emitting diodes (LEDs) with qualitatively different narrow spectra, we describe wavelength dependence of light capture, electron transport and energy transduction to main cellular pools. In addition, we describe processes that fine-tune light capture, such as state transitions, or the efficiency of energy transfer from phycobilisomes to photosystems (PS). We show that growth was the most limited under blue light due to inefficient light harvesting, and that many cellular processes are tightly linked to the redox state of the plastoquinone (PQ) pool, which was the most reduced under red light. The PSI-to-PSII ratio was low under blue photons, however, it was not the main growth-limiting factor, since it was even more reduced under violet and near far-red lights, where Synechocystis grew faster compared to blue light. Our results provide insight into the spectral dependence of phototrophic growth and can provide the foundation for future studies of molecular mechanisms underlying light acclimation in cyanobacteria, leading to light optimization in controlled cultivations.

Interfacial Charge Transfer in Photoexcited QD-Molecule Composite of Tetrahedral CdSe Quantum Dot Coupled with Carbazole.

Photoexcited charge transfer dynamics in CdSe quantum dots (QDs) coupled with carbazole were explored to model QD-molecule systems for light-harvesting applications. The absorption spectra of QDs with different sizes, i.e., Cd35Se20X30L30 (T1), Cd56Se35X42L42 (T2), and Cd84Se56X56L56 (T3) were simulated with quantum dynamical methods, which qualitatively match the reported experimental spectra. The carbazole is attached with a 3-amino group at the apex position of T1 (namely T1-3A-Cz), establishing proper electronic communication between T1 and carbazole. The spectra of T1-3A-Cz is 0.22 eV red-shifted compared to T1. A time-dependent perturbation was applied in tune with the lowest energy peak (3.63 eV) of T1-3A-Cz to investigate the charge transfer dynamics, which revealed an ultrafast charge separation within the femtosecond time scale. The electronic structure showed a favorable energy alignment between T1 and carbazole in T1-3A-Cz. The LUMO of carbazole was situated below the conduction band of the QD, while the HOMO of carbazole mixed perfectly with the top of the valence band of the QD, developing the interfacial charge transfer states. These states promoted the photoexcited electron transfer directly from the CdSe core to carbazole. A rapid and enhanced charge separation occurred with the laser field strength increasing from 0.001 to 0.005 V/Å. However, T1 connected to the other positions of carbazole did not show charge separation effectively. The photoinduced charge transfer is negligible in the case of T2-carbazole systems due to poor electronic coupling, and it is not observed in T3-carbazole systems. So, the T1-3A-Cz model acts as a perfect donor-acceptor QD-molecule nanocomposite that can harvest photon energy efficiently. Further enhancement of charge transfer can be achieved by coupling more carbazoles to the T1 QD (e.g., T1-3A-Cz2) due to the extension of hole delocalization between T1 and the carbazoles.

Theoretical, structural, and electronic analyses of pyridin-based dyes for dye-sensitized solar cells applications.

CONTEXT: The new series of donor-π-acceptor dyes have been designed using pyridine derivatives as a donor group and thienothiophene as a π-spacer group, which were linked via 10 acceptor groups. The highest occupied molecular orbital energies range from - 6.177 to - 5.786 eV, whereas the lowest unoccupied molecular orbital energies range from - 2.181 to - 3.664 eV. A6 dye has smaller energy gap, lower hardness, higher electrophilicity index, and good photovoltaic performance than other sensitizers. The lowest dihedral angle is observed in A1, A2, A6, A7, and A8 which are appropriate for intramolecular charge transfer between the molecules. The A8 has higher light harvesting efficiency, which increases the photovoltaic efficiency of the designed dye. The A6, A7, and A8 dyes spend less time in the excited state, which means they emit photons more efficiently than other dyes. The interaction between donor to π-spacer (red line) parts of the dyes has the bonding interaction (positive), and π-spacer to acceptor (blue line) parts of the dyes have the bonding and antibonding (negative) behaviours. The dyes A5 and A9 have 305.79 and 357.71 times higher ß0 values than urea (0.781 × 10-30 esu) molecules. The spectral properties of the A6 dye strongly affect the structural modification. METHODS: The density functional theory (DFT) and time-dependent DFT (TD-DFT) approach B3LYP/6-311G (d,p) basic set were used to optimize the designed dyes. All the calculations are performed using Gauss view 6.0 and Gaussian 09 software. The density of state spectrum is plotted using Gauss sum 2.6.

Comprehensive Study of Artificial Light-Harvesting Systems with a Multi-Step Sequential Energy Transfer Mechanism.

Artificial light-harvesting systems (LHSs) with a multi-step sequential energy transfer mechanism significantly enhance light energy utilization. Nonetheless, most of these systems exhibit an overall energy transfer efficiency below 80%. Moreover, due to challenges in molecularly aligning multiple donor/acceptor chromophores, systems featuring ≥3-step sequential energy transfer are rarely reported. Here, a series of artificial LHSs is introduced featuring up to 4-step energy transfer mechanism, constructed using a cyclic peptide-based supramolecular scaffold. These LHSs showed remarkably high energy transfer efficiencies (≥90%) and satisfactory fluorescence quantum yields (ranging from 17.6% to 58.4%). Furthermore, the structural robustness of the supramolecular scaffold enables a comprehensive study of these systems, elucidating the associated energy transfer pathways, and identifying additional energy transfer processes beyond the targeted sequential energy transfer. Overall, this comprehensive investigation not only enhances the understanding of these LHSs, but also underscores the versatility of cyclic peptide-based supramolecular scaffolds in advancing energy harvesting technologies.

Light harvesting in purple bacteria does not rely on resonance fine-tuning in peripheral antenna complexes.

The ring-like peripheral light-harvesting complex 2 (LH2) expressed by many phototrophic purple bacteria is a popular model system in biological light-harvesting research due to its robustness, small size, and known crystal structure. Furthermore, the availability of structural variants with distinct electronic structures and optical properties has made this group of light harvesters an attractive testing ground for studies of structure-function relationships in biological systems. LH2 is one of several pigment-protein complexes for which a link between functionality and effects such as excitonic coherence and vibronic coupling has been proposed. While a direct connection has not yet been demonstrated, many such interactions are highly sensitive to resonance conditions, and a dependence of intra-complex dynamics on detailed electronic structure might be expected. To gauge the sensitivity of energy-level structure and relaxation dynamics to naturally occurring structural changes, we compare the photo-induced dynamics in two structurally distinct LH2 variants. Using polarization-controlled 2D electronic spectroscopy at cryogenic temperatures, we directly access information on dynamic and static disorder in the complexes. The simultaneous optimal spectral and temporal resolution of these experiments further allows us to characterize the ultrafast energy relaxation, including exciton transport within the complexes. Despite the variations in PPC molecular structure manifesting as clear differences in electronic structure and disorder, the energy-transport and-relaxation dynamics remain remarkably similar. This indicates that the light-harvesting functionality of purple bacteria within a single LH2 complex is highly robust to structural perturbations and likely does not rely on finely tuned electronic- or electron-vibrational resonance conditions.