Carbon dot-based artificial light-harvesting systems with sequential energy transfer and white light emission for photocatalysis

In this work, we designed and synthesized cationic carbon dots(CDs) with a size distribution of 1.6–3.7 nm, which exhibited dark blue fluorescence in the aqueous solution. Based on its excellent luminescence properties, we used it as an energy donor to construct a sequential artificial light-harvesting system(LHS) by employing the energy-matching dyes eosin Y disodium salt(EY) and sulforhodamine101(SR101), which could regulate the white light emission(Commission Internationale de l'Eclairage(CIE) coordinate:(0.30, 0.31)) with the energy transfer efficiency(ΦET) of 53.9% and 20.0%. Moreover, a single-step artificial LHS with white light emission(0.32, 0.28) can be constructed directly using CDs and dye solvent 43(SR) with ΦETand antenna effect(AE) of 48.8% and 6.5, respectively. More importantly,CDs-based artificial LHSs were firstly used in photocatalytic of α-bromoacetophenone, with a yield of90%. This work not only provides a new strategy for constructing CDs-based LHSs, but also opens up a new application for further applying the energy harvested in CDs-based LHSs to the field of the aqueous solution photocatalysis.

Recent advances in two-step energy transfer light-harvesting systems driven by non-covalent self-assembly

Sequential energy transfer is ubiquitous in natural light-harvesting systems(LHSs),which greatly promotes the exploitation of light energy.The LHSs in nature are sophisticated supramolecular assemblies of chlorophyll molecules that carry out efficient light harvesting through cascade energy transfer process.Inspired by nature,scientists have paid much attention to fabricate stepwise LHSs based on assorted supramolecular scaffolds in recent years.Light-harvesting antennas and energy acceptors can be accommodated in particular scaffolds,which offer great convenience for energy transfer between them.These systems not only further mimic photosynthesis,but also demonstrate many potential applications,such as photocatalysis,tunable luminescence,and information encryption,etc.In this review article,aiming at offering a practical guide to this emerging research field,the introduction of construction strategies towards sequential LHSs will be presented.Different scaffolds are classified and highlighted,including host-guest assemblies,metal-coordination assemblies,as well as bio-macromolecular and other supramolecular scaffolds.

Assembly of highly efficient aqueous light-harvesting system from sequence-defined peptoids for cytosolic microRNA detection

Precisely controlled spatial distributions of artificial light-harvesting systems in aqueous media are of significant importance for mimicking natural light-harvesting systems;however,they are often restrained by the solubility and the aggregation-caused quenching effect of the hydrophobic chromophores.Herein,we report one highly efficient artificial light-harvesting system based on peptoid nanotubes that mimic the hierarchical cylindrical structure of natural systems.The high crystallinity of these nanotubes enabled the organization of arrays of donor chromophores with precisely controlled spatial distributions,favoring an efficient Förster resonance energy transfer(FRET)process in aqueous media.This FRET system exhibits an extremely high efficiency of 98.6%with a fluorescence quantum yield of 40%and an antenna effect of 29.9.We further demonstrated the use of this artificial light-harvesting system for quantifying miR-210 within cancer cells.The fluorescence intensity ratio of donor to acceptor is linearly related to the concentration of intercellular miR-210 in the range of 3.3–156 copies/cell.Such high sensitivity in intracellular detection of miR-210 using this artificial light-harvesting system offers a great opportunity and pathways for biological imaging and detection,and for the further creation of microRNA(miRNA)toolbox for quantitative epigenetics and personalized medicine.

Construction and application of the polyelectrolyte-based sequential artificial light-harvesting system

In this work,we have designed and synthesized a cyano-substituted p-phenylenevinylene derivative(PPTA),which can self-assemble into positively charged nanoparticles in an aqueous solution with a deep green fluorescence.An anionic polyelectrolyte material guar gum modified by carboxylic acid(GP5A)was chosen to build an artificial light-harvesting system(LHS)through self-assembly with PPTA,in which two acceptors Eosin Y(EY)and Nile red(NiR)were loaded into the PPTA-GP5A assemblies through electrostatic interaction and Van der Waals force.By adjusting the molar ratio of PPTA-GP5A/EY at 1:0.004,the one-step artificial LHS can exhibit high energy transfer efficiency(Φ_(ET))(38.9%)and antenna effect(AE)(4.6).Subsequently,with the addition of NiR,theΦET and AE of the two-step sequential artificial LHS were calculated to be 71.9%and 13.5,respectively.Moreover,the two-step artificial LHS constructed by the polyelectrolyte material GP5A can be used as a nanoreactor to photocatalyst alkylation of C-H bonds of phenyl vinyl sulfone(PVS)and tetrahydrofuran(THF)in water with a yield of 42%.Therefore,we have constructed an artificial LHS with two-step energy transfer based on polyelectrolytes through the electrostatic interaction to improve energy transfer efficiency,which can also be used as a nanoreactor for photocatalysis.

Artificial light-harvesting systems and their applications in photocatalysis and cell labeling

Photosynthesis is the basis for the survival of organisms in nature;consequently,the fabrication of artificial light-harvesting systems(LHSs)that simulate natural photosynthesis is of significant interest.Recently,a variety of artificial LHSs have been successfully constructed using fluorescence resonance energy transfer(FRET).However,it is crucial to fabricate artificial LHSs with a sequential energy transfer process when considering that the natural photosynthetic process involves a multistep sequential energy transfer process rather than a simple one-step energy transfer.Moreover,many previously reported LHSs have been used as imaging agents for cell labeling and bioimaging or as catalysts in photocatalytic reactions,showing promise for applications simulating natural photosynthesis.In this review,we have summarized recently published representative work on artificial LHSs.In addition,the application of LHSs in photocatalysis and cell labeling has been described in detail.

Artificial light-harvesting systems fabricated by supramolecular host–guest interactions

Artificial light-harvesting systems(LHSs) have drawn increasing research interest in recent times due to the energy crisis worldwide. Concurrently, macrocycle-based host–guest interactions have played an important role in the development of supramolecular chemistry. In recent years, studies towards artificial LHSs driven by macrocycle-based host–guest interactions are gradually being disclosed. In this mini-review, we briefly introduce the burgeoning progress of artificial LHSs driven by host–guest interactions. We believe that an increasing number of reports of artificial LHSs driven by host–guest interactions will appear in the near future and will provide a viable alternative for the future production of renewable energy.

An Artificial Light-Harvesting System with Tunable Fluorescence Color in Aqueous Sodium Dodecyl Sulfonate Micellar Systems for Photochemical Catalysis

Main observation and conclusion In the present work,an artificial light-harvesting system with fluorescence resonance energy transfer(FRET)is successfully fabricated in aqueous sodium dodecyl sulfonate(SDS)micellar systems.Since the tight and orderly arrangement of dodecyl in the SDS micelles is hydrophobic,tetra-(4-pyridylphenyl)ethylene(4PyTPE)can be easily encapsulated into the hydrophobic layer of SDS micelles through noncovalent interaction,which exhibits aggregation-induced emission(AIE)phenomenon and can be used as energy donor.By using amphoteric sulforhodamine 101(SR101)fluorescent dye attached to the negatively charged surface of SDS micelles through electrostatic interaction as energy acceptor,the light-harvesting FRET process can be efficiently simulated.Through the steady-state emission spectra analysis in the micelle-mediated energy transfer from 4PyTPE to SR101,the fluorescence emission can be tuned and white light emission with CIE coordinates of(0.31,0.29)can be successfully achieved by tuning the donor/acceptor ratio.More importantly,to better mimic natural photosynthesis,the SDS micelles with 4PyTPE and SR101 FRET system showed enhanced catalytic activity in photochemical catalysis for dehalogenation ofα-bromoacetophenone in aqueous solution and the photocatalytic reaction could be extended to gram levels.

Characteristics and phylogeny of light-harvesting complex gene encoded proteins from marine red alga Griffithsia japonica

Six genes encoding light-harvesting complex (LHC) protein have been characterized in the multicellular red alga Griffithsia japonica EST analysis. Three of them were full sequences while others were partial sequences with 3'-UTRs. The cleavage sites between signal peptide and mature LHC protein were analyzed on these three full sequences. The sequence characteristics, calculated molecular weights and isoelectric point (pI) values and hydrophobicity of the mature proteins were deduced and analyzed. Comparing the LHC sequences of G. japonica with higher plant, Chlorophyta, chromophytes and other red algae, the high conservation of the chlorophyll (Chl) binding site among chromophytes and red algae were revealed. Phylogenetic analysis on LHC proteins from higher plant, green algae, euglena, brown algae, diatom, cryptomonad, Raphidophyte and red algae reveals that (1) there are two distinct groups of Chl a/b and Chl a/c -binding LHC; (2) Chl a binding proteins of red algae share greater similarities with the Chl a/c-binding proteins of the chromophytes and dinoflagellate than with the Chl a/b - binding proteins of the green algae and higher plants; (3) chromophyte's LHC is supposed to be evolved from red algae LHC.

Energy transfer between two aggregates in light-harvesting complexes

Energy transfer processes between two aggregates in a coupled chromophoric-pigment （protein） system are studied via the standard master equation approach. Each pigment of the two aggregates is modeled as a two-level system. The excitation energy is assumed to be transferred from the donor aggregate to the acceptor aggregate. The model can be used to theoretically simulate many aspects of light-harvesting complexes （LHCs）. By applying the real bio-parameters of photosynthesis, we numerically investigate the efficiency of energy transfer （EET） between the two aggregates in terms of some factors, e.g., the initial coherence of the donor aggregate, the coupling strengthes between the two aggregates and between different pigments, and the effects of noise from the environment. Our results provide evidence for that the actual numbers of pigments in the chromophoric tings of LHCs should be the optimum parameters for a high EET. We also give a detailed analysis of the effects of noise on the EET.

Theoretical study on the exciton dynamics of coherent excitation energy transfer in the phycoerythrin 545 light-harvesting complex

The experimental observation of long-lived quantum coherence in the excitation energy transfer(EET)process of the several photosynthetic light-harvesting complexes at low and room temperatures has aroused hot debate.It challenges the common perception in the field of complicated pigment molecular systems and evokes considerable theoretical efforts to seek reasonable explanations.In this work,we investigate the coherent exciton dynamics of the phycoerythrin 545(PE545)complex.We use the dissipation equation of motion to theoretically investigate the effect of the local pigment vibrations on the population transfer process.The result indicates that the realistic local pigment vibrations do assist the energy transmission.We demonstrate the coherence between different pigment molecules in the PE545 system is an essential ingredient in the EET process among various sites.The coherence makes the excitation energy delocalized,which leads to the redistribution of the excitation among all the chromophores in the steady state.Furthermore,we investigate the effects of the complex high-frequency spectral density function on the exciton dynamics and find that the high-frequency Brownian oscillator model contributes most to the exciton dynamic process.The discussions on the local pigment vibrations of the Brownian oscillator model suggest that the local heterogeneous protein environments and the effects of active vibration modes play a significant role in coherent energy transport.

Self-assembly of biomimetic light-harvesting complexes capable of hydrogen evolution

Biomimetics provides us a new perspective to understand complex biological process and strategy to fabricate functional materials. However,a great challenge still remains to design and fabricate biomimetic materials using a facile but effective method. Here, we develop a biomimetic light harvesting architecture based on one-step co-assembly of amphiphilic amino acid and porphyrin. Amphiphilic amino acid can self-assemble into nanofibers via π-stacking and hydrogen binding interactions. Negatively charged porphyrin adsorbs on the surface of the assembled nanofibers through electrostatic force, and the nanofibers further organize into porous urchin-like microspheres induced presumably by hydrophobic interaction. The assembled amphiphilic amino acid nanofibers work as a template to tune the organization of porphyrin with an architecture principle analogous to natural light harvesting complex. The co-assembled microspheres exhibit enhanced light capture due to the light reflection in the porous structure. Reaction center(platinum nanoparticles) can be effectively coupled with the light harvesting microspheres via photoreduction. After visible light illumination, hydrogen evolution occurs on the hybrid microspheres.

Preparation of coemissive luminescent nanoparticles in continuous-flow microreactors for efficient light-harvesting systems

To address the energy challenges,scientists have designed various artificial light-harvesting systems inspired by photosynthesis.Notably,for light-harvesting systems,an energytransfer efficiency close to 100%with an antenna effect greater than 10 is generally considered a good application criterion.[1]Today,building an efficient light-harvesting system at a low cost is still demanding.

Azobenzene-based ultrathin peptoid nanoribbons for the potential on highly efficient artificial light-harvesting

The development of artificial light-harvesting systems based on long-range ordered ultrathin organic nanomaterials(i.e., below3 nm), which were assembled from stimuli-responsive sequence-controlled biomimetic polymers, remains challenging. Herein,we report the self-assembly of azobenzene-containing amphiphilic ternary alternating peptoids to construct photo-responsive ultrathin peptoids nanoribbons(UTPNRs) with a thickness of ~2.3 nm and the length in several micrometers. The pendants hydrophobic conjugate stacking mechanism explained the formation of one-dimensional ultrathin nanostructures, whose thickness was highly dependent on the length of side groups. The photo-isomerization of azobenzene moiety endowed the aggregates with a reversible morphology transformation from UTPNRs to spherical micelles(46.5 nm), upon the alternative irradiation with ultraviolet and visible light. Donor of 4-(2-hydroxyethylamino)-7-nitro-2,1,3-benzoxadiazole(NBD) and acceptor of rhodamine B(RB) were introduced onto the hydrophobic and hydrophilic regions, respectively, to generate photocontrollable artificial light-harvesting systems. Compared with the spheres-based systems, the obtained NBD-UTPNRs@RB composite proved a higher energy transfer efficiency(90.6%) and a lower requirement of RB acceptors in water. A proof-ofconcept use as fluorescent writable ink demonstrated the potential of UTPNRs on information encryption.

Boosting the efficiency of quantum dot–sensitized solar cells over 15%through light-harvesting enhancement

How to improve the capacity of light-harvesting is still an important point and essential strategy for the assembling of high-efficiency quantum dot–sensitized solar cells(QDSCs).A believable approach is to implant new light absorption materials into QDSCs to stimulate the charge transfer.Herein,the few-layer black phosphorus quantum dots(BPQDs)are synthesized by electrochemical intercalation technology using bulk BP as source.Then the obtained BPQDs are deposited onto the surface of Zn–Cu–In–S–Se(ZCISSe)QD-sensitized TiO2 substrate to serve as another light-harvesting material for the first time.The experimental results have shown that BPQDs can not only increase the absorption intensity by photoanode but also reduce unnecessary charge recombination processes at the interface of photoanode/electrolyte.Through optimizing the size and deposition process of BPQDs,the champion power conversion efficiency of ZCISSe QDSCs is increased to 15.66%(26.88 mA/cm2,Voc=0.816 V,fill factor[FF]=0.714)when compared with the original value of 14.11%(Jsc=25.41 mA/cm^(2),Voc=0.779 V,FF=0.713).

Assembling aggregation-induced emission with natural DNA to maximize donor/acceptor ratio for efficient light-harvesting antennae

Arranging dense donors around a single acceptor for the assembly of effi-cient light-harvesting antennas is a long-standing challenge due to the intractable aggregation-caused quenching of dense donors.Herein,we designed a cationic aggregation-induced emission(AIE)amphiphile to self-assemble with natural DNA duplexes.As an efficient donor,the as-prepared cationic AIE amphiphile could be densely attached to the phosphate groups of natural DNA duplexes by using the smaller cationic trimethylammonium.The long alkyl chain between the cationic trimethylammonium and the AIEfluorophore allowed for avoiding the insuffi-cient binding caused by the steric hindrance of the AIEfluorophore,resulting in a remarkably high donor/acceptor ratio comparable to that of the widely developed custom DNA assemblies.The proposed self-assembly strategy provided novelflex-ible avenues for the assembling offinely controlled and efficient light-harvesting systems into natural DNA with little synthetic modifications and low cost.

Novel Evidence for a Reversible Dissociation of Light-harvesting Complex II from Photosystem II Reaction Center Complex Induced by Saturating Light Illumination in Soybean Leaves

After saturating light illumination for 3 h the potential photochemical efficiency of photosystem Ⅱ （PSII） （FJF,, the ratio of variable to maximal fluorescence） decreased markedly and recovered basically to the level before saturating light illumination after dark recovery for 3 h in both soybean and wheat leaves, indicating that the decline in FJ/Fm is a reversible down-regulation. Also, the saturating light illumination led to significant decreases in the low temperature （77 K） chlorophyll fluorescence parameters F685 （chlorophyll a fluorescence peaked at 685 nm） and F685/F735 （F735, chlorophyll a fluorescence peaked at 735 nm） in soybean leaves but not in wheat leaves. Moreover, trypsin （a protease） treatment resulted in a remarkable decrease in the amounts of PsbS protein （a nuclear gene psbS-encoded 22 kDa protein） in the thylakoids from saturating light-illuminated （SI）, but not in those from darkadapted （DT） and dark-recovered （DRT） soybean leaves. However, the treatment did not cause such a decrease in amounts of the PsbS protein in the thylakoids from saturating light-illuminated wheat leaves. These results support the conclusion that saturating light illumination induces a reversible dissociation of some light-harvesting complex Ⅱ （LHClI） from PSII reaction center complex in soybean leaf but not in wheat leaf.

Regulation of Reversible Dissociation of LHCII from PSII by Phosphorylation in Plants

LHCII is a crucial light-harvesting pigment/protein complex in photosystem II (PSII) supercomplex. It also participates in the light energy redistribution between photosystems and in the photoprotection via its reversible dissociation with PSII and PSI (photosystem I). This reversible detachment of LHCII is regulated by phosphorylation of its own and PSII core protein. Under low light conditions, LHCII is phosphorylated and dissociated with PSII core protein complex and combined with PSI, which balances the excitation energy between PSII and PSI;Under high light environment, the phosphorylation of PSII core proteins makes LHCII detach from PSII. The dissociated LHCII presents in a free state, which involves in the thermal dissipation of excess excitation energy. During photodamage, dual phosphorylations of both PSII core proteins and LHCII complexes occur. The phosphorylation of D1 is conductive to the disintegration of photodamaged PSII and the cycle of repair. In this circumstance, the phosphorylation of LHCII is induced by reactive oxygen species (ROS) and then the phosphorylated LHCII migrates to PSI, into the repair cycle of damaged PSII. The ferredoxin (Fdr) and thioredoxin (Tdr) system may play a possible central role in the phosphorylation regulation on LHCII dissociation.

Heterojunction Incorporating Perovskite and Microporous Metal–Organic Framework Nanocrystals for Efficient and Stable Solar Cells

In this paper,we present a facile approach to enhance the efficiency and stability of perovskite solar cells(PSCs)by incorporating perovskite with microporous indium-based metal–organic framework[In12O(OH)16(H2O)5(btc)6]n(In-BTC)nanocrystals and forming heterojunction light-harvesting layer.The interconnected micropores and terminal oxygen sites of In-BTC allow the preferential crystallization of perovskite inside the regular cavities,endowing the derived films with improved morphology/crystallinity and reduced grain boundaries/defects.Consequently,the In-BTC-modified PSC yields enhanced fill factor of 0.79 and power conversion efficiency(PCE)of 20.87%,surpassing the pristine device(0.76 and 19.52%,respectively).More importantly,over 80%of the original PCE is retained after 12 days of exposure to ambient environment(25°C and relative humidity of^65%)without encapsulation,while only about 35%is left to the pristine device.

YGL9, encoding the putative chloroplast signal recognition particle 43 kDa protein in rice, is involved in chloroplast development

The nuclear-encoded light-harvesting chlorophyll a/b-binding proteins（LHCPs） are specifically translocated from the stroma into the thylakoid membrane through the chloroplast signal recognition particle（cp SRP） pathway. The cp SRP is composed of a cp SRP43 protein and a cp SRP54 protein, and it forms a soluble transit complex with LHCP in the chloroplast stroma. Here, we identified the YGL9 gene that is predicted to encode the probable rice cp SRP43 protein from a rice yellow-green leaf mutant. A phylogenetic tree showed that an important conserved protein family, cp SRP43, is present in almost all green photosynthetic organisms such as higher plants and green algae. Sequence analysis showed that YGL9 comprises a chloroplast transit peptide, three chromodomains and four ankyrin repeats, and the chromodomains and ankyrin repeats are probably involved in protein-protein interactions. Subcellular localization showed that YGL9 is localized in the chloroplast. Expression pattern analysis indicated that YGL9 is mainly expressed in green leaf sheaths and leaves. Quantitative real-time PCR analysis showed that the expression levels of genes associated with pigment metabolism, chloroplast development and photosynthesis were distinctly affected in the ygl9 mutant. These results indicated that YGL9 is possibly involved in pigment metabolism, chloroplast development and photosynthesis in rice.

Changes in Thermostability of Photosystem Ⅱ and Leaf Lipid Composition of Rice Mutant with Deficiency of Light-harvesting Chlorophyll a/b Protein Complexes

We studied the difference in thermostability of photosystem Ⅱ （PSII） and leaf lipid composition between a T-DNA insertion mutant rice （Oryza sativa L.） VG28 and its wild type Zhonghuau. Native green gel and SDS-PAGE electrophoreses revealed that the mutant VG28 lacked all light-harvesting chlorophyll a/b protein complexes. Both the mutant and wild type were sensitive to high temperatures, and the maximal efficiency of PSII photochemistry （FJ Fm） and oxygen-evolving activity of PSII in leaves significantly decreased with increasing temperature. However, the PSII activity of the mutant was markedly more sensitive to high temperatures than that of the wild type. Lipid composition analysis showed that the mutant had less phosphatidylglycerol and sulfoquinovosyl diacylglycerol compared with the wild type. Fatty acid analysis revealed that the mutant had an obvious decrease in the content of 16：1t and a marked increase in the content of 18：3 compared with the wild type. The effects of lipid composition and unsaturation of membrane lipids on the thermostability of PSII are discussed.