Efficient Light-harvesting Systems Research Articles

Multi-Step and Switchable Energy Transfer in Photoluminescent Organosilicone Capsules.

Light-harvesting is of vital importance for many events, such as photosynthesis. To efficiently gather and transfer solar energy, delicate antenna is needed, which has been achieved by algae and plants. However, construction of efficient light-harvesting systems using multiple, artificial building blocks is still challenging. Here, blue-emitting organosilicone capsules containing carbon dots (denoted as CDs-Si) in ethanol are prepared, which can effectively transfer energy to green-emitting (silicone-functionalized bodipy, Si-BODIPY) or red-emitting (rhodamine b, RhB) dyes. In ternary system, sequential Förster resonance energy transfer from CDs-Si to Si-BODIPY and further to RhB is realized, which is accompanied with a less pronounced, parallel FRET directly from CDs-Si to RhB. The overall efficiency of energy transfer reaches ≈86%. By introducing a photoswitch (1,2-bis(2,4-dimethyl-5-phenyl-3-thienyl)-3,3,4,4,5,5-hexafluoro-1-cyclopentene, DAE) to the system, the emission becomes switchable under alternative illumination with UV and visible light, leading to the formation of smart artificial light-harvesting systems.

Platinum Metallacycle-Based Molecular Recognition: Establishment and Application in Spontaneous Formation of a [2]Rotaxane with Light-Harvesting Property.

Macrocyclic molecule-based host-guest systems, which provide contributions for the design and construction of functional supramolecular structures, have gained increasing attention in recent years. In particular, platinum(II) metallacycle-based host-guest systems provide opportunities for chemical scientists to prepare novel materials with various functions and structures due to the well-defined shapes and cavity sizes of platinum(II) metallacycles. However, the research on platinum(II) metallacycle-based host-guest systems has been given little attention. In this article, we demonstrate the host-guest complexation between a platinum(II) metallacycle and a polycyclic aromatic hydrocarbon molecule, naphthalene. Taking advantage of metallacycle-based host-guest interactions and the dynamic property of reversible Pt coordination bonds, a [2]rotaxane is efficiently prepared by employing a template-directed clipping procedure. The [2]rotaxane is further applied to the fabrication of an efficient light-harvesting system with multi-step energy transfer process. This work comprises an important supplement to macrocycle-based host-guest systems and demonstrates a strategy for efficient production of well-defined mechanically interlocked molecules with practical values.

The Unique Light-Harvesting System of the Algal Phycobilisome: Structure, Assembly Components, and Functions.

The phycobilisome (PBS) is the major light-harvesting apparatus in cyanobacteria and red algae. It is a large multi-subunit protein complex of several megadaltons that is found on the stromal side of thylakoid membranes in orderly arrays. Chromophore lyases catalyse the thioether bond between apoproteins and phycobilins of PBSs. Depending on the species, composition, spatial assembly, and, especially, the functional tuning of different phycobiliproteins mediated by linker proteins, PBSs can absorb light between 450 and 650 nm, making them efficient and versatile light-harvesting systems. However, basic research and technological innovations are needed, not only to understand their role in photosynthesis but also to realise the potential applications of PBSs. Crucial components including phycobiliproteins, phycobilins, and lyases together make the PBS an efficient light-harvesting system, and these provide a scheme to explore the heterologous synthesis of PBS. Focusing on these topics, this review describes the essential components needed for PBS assembly, the functional basis of PBS photosynthesis, and the applications of phycobiliproteins. Moreover, key technical challenges for heterologous biosynthesis of phycobiliproteins in chassis cells are discussed.

Artificial stepwise light harvesting system in water constructed by quadruple hydrogen bonding supramolecular polymeric nanoparticles

Stepwise energy transfer is ubiquitous in natural photosynthesis, which greatly promotes the widespread use of solar energy. Herein, we constructed a supramolecular light harvesting system based on sequential energy transfer through the hierarchical self-assembly of M, which contains a cyanostilbene core flanked by two ureidopyrimidinone motifs, endowing itself with both aggregation-induced emission behavior and quadruple hydrogen bonding ability. The monomer M can self-assemble into hydrogen bonded polymers and then form supramolecular polymeric nanoparticles in water through a mini-emulsion process. The nanoparticles were further utilized to encapsulate the relay acceptor ESY and the final acceptor NDI to form a two-step FRET system. Tunable fluorescence including a white-light emission was successfully achieved. Our work not only shows a desirable way for the fabrication of efficient two-step light harvesting systems, but also shows great potential in tunable photoluminescent nanomaterials.

High-Performance Light-Harvesting Cotton Fiber Photocatalyst Inspired by “Ring Dyeing” for the Cross-Dehydrogenative Coupling Reaction

Highly efficient light-harvesting systems (LHSs) with the sequential energy transfer process are important for utilizing solar energy in photosynthesis. However, most light-harvesting systems are nanoparticles and vesicles, which are difficult to prepare and recycle. In this paper, we developed a light-harvesting system based on amino-methyl coumarin acid (AMCA), C.I. Basic Yellow 40 (BY 40), and phloxine B (PhB) organic dyes for photocatalytic cross-dehydrogenative coupling (CDC) reactions. The conversion of the CDC reaction using the AMCA–BY 40–PhB system could reach 98.77% in ethanol, which was much higher than that with the main active catalyst PhB alone. In order to recycle and reuse the above catalysts, a facile, simple, and highly efficient light-harvesting cotton photocatalyst AMCA/BY 40/β-SCD-PhB-MCFs was prepared via three steps of cationization of cotton fibers (MCFs), sulfobutylether-β-cyclodextrin (β-SCD) inclusion of donor fluorophores, and final immobilization of fluorophores. These light-harvesting cotton fibers showed excellent catalytic performance, and the catalysis rate of the CDC reaction was 1.57 times higher than that of the PhB-MCFs alone. Its special “ring dyeing” and hierarchical pore structure provided a favorable microenvironment for photocatalysis. The wide range in light absorption, highly efficient energy transfer (53.1%), and antenna efficiency (15.6) of the light-harvesting cotton fiber synergistically enhanced the energy transfer process. Furthermore, the light-harvesting cotton fibers showed high reusability, which could be easily recovered and reused five times without significant catalyst leaching. More interestingly, the fiber could be easily loaded in microchannels of the continuous flow reactor to catalyze the CDC reaction, which successfully achieved gram-scale photosynthesis due to the large specific surface area and easy mass transfer of fiber catalysts.

Predicted Structure of the BciC Enzyme Catalyzing the Removal of the C132-Methoxycarbonyl Group for Biosynthesis of Chlorosomal Chlorophylls: A Mechanism for Dual Catalytic Functions of Hydrolysis and Decarboxylation inside Its Active Site.

Green photosynthetic bacteria, one of the phototrophs, have the largest and most efficient light-harvesting antenna systems, called chlorosomes. The core part of chlorosomes consists of unique bacteriochlorophyll c/d/e molecules. In the biosynthetic pathway of these molecules, a BciC enzyme catalyzes the removal of the C132-methoxycarbonyl group of chlorophyllide a. Two sequential reactions have been proposed for the BciC enzymatic demethoxycarbonylation: the BciC enzyme would catalyze the hydrolysis of the C132-methoxycarbonyl group, and the resulting carboxylic acid would be rapidly decarboxylated to generate pyrochlorophyllide a. In this study, we computationally predicted the three-dimensional structure of the BciC protein. Its active site was proposed based on structural analysis using docking simulation. In vitro enzymatic reaction assays of mutated BciC supported the prediction. The BciC enzymatic hydrolysis would be an aspartic/glutamic acid hydrolase, which involves the amino residues E85 and D180. Furthermore, Y58 and H126 might depend on stabilization and/or recognition with the substrate. Most importantly, H137 would protonate 13-C═O or deprotonate C132-COOH in the hydrolyzed product to promote decarboxylation. In conclusion, the BciC enzyme has the dual functions of hydrolysis and decarboxylation.

Highly efficient sequential light-harvesting system constructed by macrocycle-based nanoparticles for tunable photoluminescence

Efficient energy transfer is ubiquitous in natural light-harvesting systems (LHSs), which has inspired humans to develop various carrier platforms and energy transfer strategies to mimic nature. In this study, we employ pillar [5]arene-mediated nanoparticles as the nano-platform and a sequential energy transfer strategy to achieve a highly efficient LHS. Specifically, by incorporating the hydrophobic dye, eosin Y (ESY) into the nanoparticles as a relay acceptor, the excitation energy from the host-guest donor WP5⸧G can be efficiently transferred to the final acceptor, sulforhodamine 101 (SR101), making the overall donor energy transfer efficiency up to 94%. Under this condition, the radiative rate constant (kr) of WP5⸧G is almost 8 times higher, and the emission brightness (ε(λabs) × φF) is nearly doubled, indicative of the rapid and efficient energy transfer process. Finally, the as-prepared LHS nanoparticles were applied to LED devices to achieve color-tunable photoluminescence. This work demonstrates a fabrication strategy for highly efficient light-harvesting systems that holds great potential for manufacturing bright organic luminescent materials.

Protein Orientation Defines Rectification of Electronic Current via Solid-State Junction of Entire Photosystem-1 Complex.

We demonstrate that the direction of current rectification via one of nature's most efficient light-harvesting systems, the photosystem 1 complex (PS1), can be controlled by its orientation on Au substrates. Molecular self-assembly of the PS1 complex using four different linkers with distinct functional head groups that interact by electrostatic and hydrogen bonds with different surface parts of the entire protein PS1 complex was used to tailor the PS1 orientation. We observe an orientation-dependent rectification in the current-voltage characteristics for linker/PS1 molecule junctions. Results of an earlier study using a surface two-site PS1 mutant complex having its orientation set by covalent binding to the Au substrate supports our conclusion. Current-voltage-temperature measurements on the linker/PS1 complex indicate off-resonant tunneling as the main electron transport mechanism. Our ultraviolet photoemission spectroscopy results highlight the importance of the protein orientation for the energy level alignment and provide insight into the charge transport mechanism via the PS1 transport chain.

Purification of Active Photosystem I-Light Harvesting Complex I from Plant Tissues.

This method is used to isolate Photosystem I (PSI) together with the Light Harvesting Complex I (LHCI), its native antenna, from plants. PSI-LHCI is a large membrane protein complex coordinating hundreds of light harvesting and electron transport factors and is the most efficient light harvesting system found in nature. Photons absorbed by the four LHCA antenna proteins that make up LHCI are transferred through excitonic interaction to the PSI core reaction center and are used to facilitate light-driven charge separation across the thylakoid membrane, providing reducing power and energy for carbon fixation in photoautotrophic organisms. The high quantum efficiency of PSI makes this complex an excellent model to study light-driven energy transfer. In this protocol, plant tissue is mechanically homogenized, and the chloroplasts are separated from the bulk cellular debris by filtration and centrifugation. The isolated chloroplasts are then osmotically lysed, and the thylakoid membranes are recovered via centrifugation and solubilized using the detergent n-dodecyl-beta-maltoside. The solubilized material is loaded onto an anion exchange column to collect most of the chlorophyll-containing complexes. Larger complexes are precipitated from the solution, resuspended in a small volume, and loaded on sucrose gradients to separate the major chlorophyll-containing complexes. The resulting sucrose gradient fractions are characterized to identify the band of interest containing PSI-LHCI. This protocol is highly similar to the protocol used in the crystallization of plant PSI-LHCI with some simplifications and relies on methods developed over the years in the lab of Nathan Nelson.

Contrasting luminescence in heparin and DNA-templated co-assemblies of dimeric cyanostilbenes: efficient energy transfer in heparin-based co-assemblies.

Dimeric cationic cyanostilbenes with peripheral alkyl chains demonstrated aggregation in aqueous media depending on the length of the hydrophobic segment and produced luminescent spherical nano-assemblies in the case of long alkyl chain derivatives. In the presence of heparin, a bio-polyanion that is routinely used as an anticoagulant, the self-assembled structures obtained from the amphiphilic dimers showed the formation of higher-order structures whereas the non-assembling dimers exhibited heparin-induced supramolecular structure formation. In both cases, a significant enhancement in the emission was observed. This led to the detection of heparin in aqueous buffer, serum and plasma with a "turn-on" fluorescence response. Interestingly, these derivatives also exhibited luminescence variation in the presence of ctDNA. However, the response towards DNA was opposite to that observed in the case of heparin i.e., "turn-off'' fluorescence response. Notably, depending on the length of the alkyl segment, divergent DNA binding modes of these derivatives were observed. Due to their enhanced luminescence, the heparin-based co-assemblies were further explored as artificial light-harvesting systems exhibiting an efficient energy transfer process to embedded acceptor dyes with a high antenna effect.

PH-tunable phosphorescence and light harvesting in cucurbit[8]uril host-guest assemblies.

Host-guest assemblies of halo-phenyl pyridine derivatives and cucurbit[8]uril (CB[8]) exhibited pH-responsive room temperature phosphorescence (RTP) in aqueous media. Moreover, they acted as efficient light-harvesting systems demonstrating triplet-singlet energy transfer to various acceptor dyes.

Harnessing photosynthesis to produce electricity using cyanobacteria, green algae, seaweeds and plants.

The conversion of solar energy into electrical current by photosynthetic organisms has the potential to produce clean energy. Life on earth depends on photosynthesis, the major mechanism for biological conversion of light energy into chemical energy. Indeed, billions of years of evolution and adaptation to extreme environmental habitats have resulted in highly efficient light-harvesting and photochemical systems in the photosynthetic organisms that can be found in almost every ecological habitat of our world. In harnessing photosynthesis to produce green energy, the native photosynthetic system is interfaced with electrodes and electron mediators to yield bio-photoelectrochemical cells (BPECs) that transform light energy into electrical power. BPECs utilizing plants, seaweeds, unicellular photosynthetic microorganisms, thylakoid membranes or purified complexes, have been studied in attempts to construct efficient and non-polluting BPECs to produce electricity or hydrogen for use as green energy. The high efficiency of photosynthetic light-harvesting and energy production in the mostly unpolluting processes that make use of water and CO2 and produce oxygen beckons us to develop this approach. On the other hand, the need to use physiological conditions, the sensitivity to photoinhibition as well as other abiotic stresses, and the requirement to extract electrons from the system are challenging. In this review, we describe the principles and methods of the different kinds of BPECs that use natural photosynthesis, with an emphasis on BPECs containing living oxygenic photosynthetic organisms. We start with a brief summary of BPECs that use purified photosynthetic complexes. This strategy has produced high-efficiency BPECs. However, the lifetimes of operation of these BPECs are limited, and the preparation is laborious and expensive. We then describe the use of thylakoid membranes in BPECs which requires less effort and usually produces high currents but still suffers from the lack of ability to self-repair damage caused by photoinhibition. This obstacle of the utilization of photosynthetic systems can be significantly reduced by using intact living organisms in the BPEC. We thus describe here progress in developing BPECs that make use of cyanobacteria, green algae, seaweeds and higher plants. Finally, we discuss the future challenges of producing high and longtime operating BPECs for practical use.

Analysis of Physiological Variations and Genetic Architecture for Photosynthetic Capacity of Japanese Soybean Germplasm.

The culmination of conventional yield improving parameters has widened the margin between food demand and crop yield, leaving the potential yield productivity to be bridged by the manipulation of photosynthetic processes in plants. Efficient strategies to assess photosynthetic capacity in crops need to be developed to identify suitable targets that have the potential to improve photosynthetic efficiencies. Here, we assessed the photosynthetic capacity of the Japanese soybean mini core collection (GmJMC) using a newly developed high-throughput photosynthesis measurement system “MIC-100” to analyze physiological mechanisms and genetic architecture underpinning photosynthesis. K-means clustering of light-saturated photosynthesis (Asat) classified GmJMC accessions into four distinct clusters with Cluster2 comprised of highly photosynthesizing accessions. Genome-wide association analysis based on the variation of Asat revealed a significant association with a single nucleotide polymorphism (SNP) on chromosome 17. Among the candidate genes related to photosynthesis in the genomic region, variation in expression of a gene encoding G protein alpha subunit 1 (GPA1) showed a strong correlation (r = 0.72, p < 0.01) with that of Asat. Among GmJMC accessions, GmJMC47 was characterized by the highest Asat, stomatal conductance (gs), stomatal density (SDensity), electron transfer rate (ETR), and light use efficiency of photosystem II (Fv’/Fm′) and the lowest non-photochemical quenching [NPQ(t)], indicating that GmJMC47 has greater CO2 supply and efficient light-harvesting systems. These results provide strong evidence that exploration of plant germplasm is a useful strategy to unlock the potential of resource use efficiencies for photosynthesis.

Highly Efficient Artificial Light-Harvesting Systems Constructed in an Aqueous Solution Based on Twisted Cucurbit[14]Uril.

Relying on the supramolecular self-assembly of twisted cucurbit[14]urils (tQ[14]), anthracene derivatives (ADPy), Nile red (NiR), and rhodamine B (RB), highly efficient light-harvesting systems have been successfully designed in an aqueous medium. The addition of tQ[14] causes ADPy to aggregate through supramolecular self-assembly to form a supramolecular polymer (ADPy@tQ[14]) with excellent aggregation-induced fluorescence and an interesting spherical external morphology, making it a remarkable energy donor. Consequently, efficient energy-transfer processes have occurred between ADPy@tQ[14] assembly and NiR and RB, which both serve as effective energy acceptors while being loaded onto ADPy@tQ[14]. In the case of NiR, the energy-transfer efficiency is up to 72.45%, and the antenna effect is near 55.4 at a donor/acceptor ratio of 100:1, making it close to the light-harvesting systems in nature. As a result, effective water-soluble artificial light-harvesting systems are showing enormous prospective as versatile platforms for simulating photosynthesis.

An efficient supramolecular artificial light-harvesting system based on twisted cucurbit[15]uril and cucurbit[10]uril for live cell imaging

The construction of highly efficient artificial light-harvesting systems in aqueous solutions is still challenging. Herein, we reported a new light-harvesting system based on the supramolecular combination of twisted cucurbit[15]uril (tQ[15]), cucurbit[10]uril (Q[10]), and an anthracene derivative (APy) with aggregation-induced emission (AIE) properties. The Q[n]-based linear supramolecular polymer, APy@tQ[15]@Q[10], was constructed through a two-step assembly strategy. Subsequently, a highly efficient artificial light-harvesting system with relatively high antenna effect and energy transfer efficiency was successfully constructed through non-covalent interactions between Rhodamine B (RB, acceptor) and the APy@tQ[15]@Q[10] (donor). The resulting system was compatible with HeLa cells and could be used for live-cell imaging in the red channel. This supramolecular assembly strategy has not only produced a highly efficient light-harvesting system but also expands the application of Q[n]s in the biomedical field.

Investigation of carrier dynamics of QDs using kinetic model and ultrafast spectroscopy

The study of carrier dynamics of QDs is extremely important for developing efficient light-harvesting systems. Here, we investigate size-dependent hole transfer from CdSe QDs to 4-aminothiophenol (4-ATPh) ligand using ultrafast spectroscopy. The photoluminescence (PL) quenching is found to be 99% and 77% for 4-ATPh ligand capped 2.9 nm and 4.3 nm QDs, respectively. We propose a stochastic model for analyzing time-resolved fluorescence decay curves of QDs to estimate the average number of ligands around QDs and it is found that the larger number of ligands are attached with smaller QDs. The analysis of TA spectroscopy data reveals that the kinetics of hole transfer from 2.9 nm QDs to ligand is faster than 4.3 nm CdSe QDs, depending on the offset between valence band (VB) of the CdSe QD and the HOMO of 4-ATPh ligands, and the average number of 4-ATPh ligands attached to each CdSe QD. The fundamental study of ligand-induced charge transfer processes in QDs is important for QD-based solar cell applications.

Multifunctionalities enabled by the synergistic effects of mesoporous carbon dots and ZnO nanorods

In this study, CD/ZnO nanohybrids were synthesised by a simple, one-pot, cost-effective method and their structure and properties were investigated by physicochemical methods. The CD/ZnO nanohybrid exhibits excellent sunlight induced photocatalytic and antibacterial activity validating the development of remarkably efficient catalytic systems and effective bactericidal agents. The IV measurements of CD/ZnO nanohybrid shows over 12-fold increase in photocurrent compared to ZnO, opening pathways for the fabrication of efficient light harvesting system. Electrochemical property measurements demonstrate that CD/ZnO nanohybrid has large integral area of cyclic voltammetry loop, demonstrating their potential for supercapacitor applications. The study presents green chemistry strategy for the synthesis of CD/ZnO nanohybrids which exhibit multifunctionalities due to the synergy between CD and ZnO. The findings of the study demonstrate the potential of CD/ZnO nanohybrids for a multitude of energy and environmental solutions.

Two-step sequential energy transfer of molecular assemblies based on host-guest interactions for the construction of photochemically catalyzed artificial light-harvesting systems

In the present work, a highly efficient artificial light-harvesting system with a two-step sequential energy transfer process based on host-guest interactions between cyano-substituted p-phenylenevinylene derivative (PPTA) and cucurbit [7]uril (CB [7]) has been constructed in an aqueous media, in which the molecular assemblies was employed as energy donors, two dyes including eosin Y (EY) and sulforhodamine (SR101) were used as energy acceptors. The obtained PPTA-CB [7] supramolecular assemblies have aggregation-induced emission (AIE) effect and can be used as an ideal donor to transfer energy to EY. Then, inspired by the multi-step energy transfer in nature, the PPTA-CB [7]+EY system was chosen as the energy donor while SR101 was selected as the energy acceptor to construct an efficient light-harvesting system with a two-step sequential energy transfer, which demonstrated high FRET efficiencies of 38% and 33% in the two-step process, respectively. The light-harvesting systems also exhibit high antenna efficiencies of 23.7 and 20.1 with a 100:1 donor/acceptor ratio, respectively. More importantly, the PPTA-CB [7]+EY + SR101 system exhibited high activity for the photocatalytic dehalogenation of 2-bromo-1-phenylethanone with a yield of up to 86% in an aqueous solution.

Probing size variations of molecular aggregates inside chlorosomes using single-object spectroscopy.

We theoretically investigate the possibility to use single-object spectroscopy to probe size variations of the bacteriochlorophyll aggregates inside chlorosomes. Chlorosomes are the light-harvesting organelles of green sulfur and non-sulfur bacteria. They are known to be the most efficient light-harvesting systems in nature. Key to this efficiency is the organization of bacteriochlorophyll molecules in large self-assembled aggregates that define the secondary structure inside the chlorosomes. Many studies have been reported to elucidate the morphology of these aggregates and the molecular packing inside them. It is widely believed that tubular aggregates play an important role. Because the size (radius and length) of these aggregates affects the optical and excitation energy transport properties, it is of interest to be able to probe these quantities inside chlorosomes. We show that a combination of single-chlorosome linear polarization resolved spectroscopy and single-chlorosome circular dichroism spectroscopy may be used to access the typical size of the tubular aggregates within a chlorosome and, thus, probe possible variations between individual chlorosomes that may result, for instance, from different stages in growth or different growth conditions.

Quantitative Förster Resonance Energy Transfer: Efficient Light Harvesting for Sequential Photo-Thermo-Electric Conversion.

Light is essential to all life on the earth. Thus, highly efficient light-harvesting systems with the sequential energy transfer process are significant for using solar energy in photosynthesis. For developing an efficient light-harvesting system, a liquid aggregation-induced emission (AIE) dye TPE-EA is obtained, as a donor and solvent, which can light up the aggregation caused quenching (ACQ) Nile Red (NiR, acceptor) to construct a quantitative Förster resonance energy transfer (FRET) system in NiR⊂TPE-EA. Impressively, this FRET pair shows an impressive photothermal effect, producing a peak temperature of 119°C while excited by UV light, with 37.8% of conversion efficiency. NiR⊂TPE-EA is quite different from most other photothermal materials, which require excitation with long wavelength light (>520nm). Therefore, NiR⊂TPE-EA firstly converts the solar into thermal energy and then into electric energy to achieve sequential photo-thermo-electric conversion. Such sequential conversion, suitable for being excited by sunlight, is anticipated to unlock new and smart approaches for capturing solar energy.