A Supramolecular Artificial Light‐Harvesting System with Two‐Step Sequential Energy Transfer for Photochemical Catalysis

An artificial light‐harvesting system with sequential energy‐transfer process was fabricated based on a supramolecular strategy. Self‐assembled from the host–guest complex formed by water‐soluble pillar[5]arene (WP5), a bola‐type tetraphenylethylene‐functionalized dialkyl ammonium derivative (TPEDA), and two fluorescent dyes, Eosin Y (ESY) and Nile Red (NiR), the supramolecular vesicles achieve efficient energy transfer from the AIE guest TPEDA to ESY. ESY can function as a relay to further transfer the energy to the second acceptor NiR and realize a two‐step sequential energy‐transfer process with good efficiency. By tuning the donor/acceptor ratio, bright white light emission can be successfully achieved with a CIE coordinate of (0.33, 0.33). To better mimic natural photosynthesis and make full use of the harvested energy, the WP5?TPEDA‐ESY‐NiR system can be utilized as a nanoreactor: photocatalyzed dehalogenation of α‐bromoacetophenone was realized with 96 % yield in aqueous medium.     

Highly Efficient Artificial Light‐Harvesting Systems Constructed in Aqueous Solution Based on Supramolecular Self‐Assembly

Highly efficient light‐harvesting systems were successfully fabricated in aqueous solution based on the supramolecular self‐assembly of a water‐soluble pillar[6]arene (WP6), a salicylaldehyde azine derivative (G), and two different fluorescence dyes, Nile Red (NiR) or Eosin Y (ESY). The WP6‐G supramolecular assembly exhibits remarkably improved aggregation‐induced emission enhancement and acts as a donor for the artificial light‐harvesting system, and NiR or ESY, which are loaded within the WP6‐G assembly, act as acceptors. An efficient energy‐transfer process takes place from the WP6‐G assembly not only to NiR but also to ESY for these two different systems. Furthermore, both of the WP6‐G‐NiR and WP6‐G‐ESY systems show an ultrahigh antenna effect at a high donor/acceptor ratio.     

Light‐Harvesting Systems Based on Organic Nanocrystals To Mimic Chlorosomes

We report the first highly efficient artificial light‐harvesting systems based on nanocrystals of difluoroboron chromophores to mimic the chlorosomes, one of the most efficient light‐harvesting systems found in green photosynthetic bacteria. Uniform nanocrystals with controlled donor/acceptor ratios were prepared by simple coassembly of the donors and acceptors in water. The light‐harvesting system funneled the excitation energy collected by a thousand donor chromophores to a single acceptor. The well‐defined spatial organization of individual chromophores in the nanocrystals enabled an energy transfer efficiency of 95 %, even at a donor/acceptor ratio as high as 1000:1, and a significant fluorescence of the acceptor was observed up to donor/acceptor ratios of 200 000:1.     

Light Harvesting and White‐Light Generation in a Composite of Carbon Dots and Dye‐Encapsulated BSA‐Protein‐Capped Gold Nanoclusters

Several strategies have been adopted to design an artificial light‐harvesting system in which light energy is captured by peripheral chromophores and it is subsequently transferred to the core via energy transfer. A composite of carbon dots and dye‐encapsulated BSA‐protein‐capped gold nanoclusters (AuNCs) has been developed for efficient light harvesting and white light generation. Carbon dots (C‐dots) act as donor and AuNCs capped with BSA protein act as acceptor. Analysis reveals that energy transfer increases from 63 % to 83 % in presence of coumarin dye (C153), which enhances the cascade energy transfer from carbon dots to AuNCs. Bright white light emission with a quantum yield of 19 % under the 375 nm excitation wavelength is achieved by changing the ratio of components. Interesting findings reveal that the efficient energy transfer in carbon‐dot–metal‐cluster nanocomposites may open up new possibilities in designing artificial light harvesting systems for future applications.     

G‐Quartet‐Based Nanostructure for Mimicking Light‐Harvesting Antenna

Artificial light‐harvesting systems have received great attention for use in photosynthetic and optoelectronic devices. Herein, a system involving G‐quartet‐based hierarchical nanofibers generated from the self‐assembly of guanosine 5′‐monophosphate (GMP) and a two‐step Förster resonance energy transfer (FRET) is presented that mimics natural light‐harvesting antenna. This solid‐state property offers advantages for future device fabrication. The generation of photocurrent under visible light shows it has potential for use as a nanoscale photoelectric device. The work will be beneficial for the development of light‐harvesting systems by the self‐assembly of supramolecular nanostructures.     

Competition between Arene–Perfluoroarene and Charge‐Transfer Interactions in Organic Light‐Harvesting Systems

Two typical types of luminescent organic cocrystals comprising pyrene–octafluoronaphthalene (pyrene–OFN) and pyrene–1,2,4,5‐tetracyanobezene (pyrene–TCNB) were developed by a simple supramolecular assembly strategy. The cocrystals exhibit distinct optical properties because of their different intermolecular interaction modes; that is, arene–perfluoroarene (AP) and charge‐transfer (CT) interactions. Unexpectedly, a pyrene–TCNB system with strong CT interactions was incorporated into a pyrene–OFN host as a robust guest to generate white‐light emission (WLE). In the supramolecular cocrystal system, an efficient energy‐transfer process from pyrene–OFN to pyrene–TCNB occurred because of the well‐matched spectra of the constituents and a desirable energy donor/acceptor (D/A) distance. The present competitive intermolecular interaction strategy could be applied to the fabrication of more complicated organic light‐harvesting systems.     

Cooperative Chirality and Sequential Energy Transfer in a Supramolecular Light‐Harvesting Nanotube

By constructing a supramolecular light‐harvesting chiral nanotube in the aqueous phase, we demonstrate a cooperative energy and chirality transfer. It was found that a cyanostilbene‐appended glutamate compound (CG) self‐assembled into helical nanotubes exhibiting both supramolecular chirality and circularly polarized luminescence (CPL). When two achiral acceptors, ThT and AO, with different energy bands were co‐assembled with the nanotube, the CG nanotube could transfer its chirality to both of the acceptors. The excitation energy could be transferred to ThT but only be sequentially transferred to AO. During this process, the CPL ascribed to the acceptor could be sequentially amplified. This work provides a new insight into the understanding the cooperative chirality and energy transfer in a chiral supramolecular system, which is similar to the natural light‐harvesting antennas.     

An Efficient Near‐Infrared Emissive Artificial Supramolecular Light‐Harvesting System for Imaging in the Golgi Apparatus

Light‐harvesting systems are an important way for capturing, transferring and utilizing light energy. It remains a key challenge to develop highly efficient artificial light‐harvesting systems. Herein, we report a supramolecular co‐assembly based on lower‐rim dodecyl‐modified sulfonatocalix[4]arene (SC4AD) and naphthyl‐1,8‐diphenyl pyridinium derivative (NPS) as a light‐harvesting platform. NPS as a donor shows significant aggregation induced emission enhancement (AIEE) after assembling with SC4AD. Upon introduction of Nile blue (NiB) as an acceptor into the NPS‐SC4AD co‐assembly, the light‐harvesting system becomes near‐infrared (NIR) emissive (675 nm). Importantly, the NIR emitting NPS‐SC4AD‐NiB system exhibits an ultrahigh antenna effect (33.1) at a high donor/acceptor ratio (250:1). By co‐staining PC‐3 cells with a Golgi staining reagent, NBD C₆‐ceramide, NIR imaging in the Golgi apparatus has been demonstrated using these NIR emissive nanoparticles.     

Artificial Light‐Harvesting Complexes Enable Rieske Oxygenase Catalyzed Hydroxylations in Non‐Photosynthetic cells

In this study, we coupled a well‐established whole‐cell system based on E. coli via light‐harvesting complexes to Rieske oxygenase (RO)‐catalyzed hydroxylations in vivo. Although these enzymes represent very promising biocatalysts, their practical applicability is hampered by their dependency on NAD(P)H as well as their multicomponent nature and intrinsic instability in cell‐free systems. In order to explore the boundaries of E. coli as chassis for artificial photosynthesis, and due to the reported instability of ROs, we used these challenging enzymes as a model system. The light‐driven approach relies on light‐harvesting complexes such as eosin Y, 5(6)‐carboxyeosin, and rose bengal and sacrificial electron donors (EDTA, MOPS, and MES) that were easily taken up by the cells. The obtained product formations of up to 1.3 g L^?1 and rates of up to 1.6 mm h^?1 demonstrate that this is a comparable approach to typical whole‐cell transformations in E. coli. The applicability of this photocatalytic synthesis has been demonstrated and represents the first example of a photoinduced RO system.     

Light‐Harvesting Photocatalysis for Water Oxidation Using Mesoporous Organosilica

An organic‐based photocatalysis system for water oxidation, with visible‐light harvesting antennae, was constructed using periodic mesoporous organosilica (PMO). PMO containing acridone groups in the framework (Acd‐PMO), a visible‐light harvesting antenna, was supported with [Ru^II(bpy)₃²⁺] complex (bpy=2,2′‐bipyridyl) coupled with iridium oxide (IrO_x) particles in the mesochannels as photosensitizer and catalyst, respectively. Acd‐PMO absorbed visible light and funneled the light energy into the Ru complex in the mesochannels through excitation energy transfer. The excited state of Ru complex is oxidatively quenched by a sacrificial oxidant (Na₂S₂O₈) to form Ru³⁺ species. The Ru³⁺ species extracts an electron from IrO_x to oxidize water for oxygen production. The reaction quantum yield was 0.34 %, which was improved to 0.68 or 1.2 % by the modifications of PMO. A unique sequence of reactions mimicking natural photosystem II, 1) light‐harvesting, 2) charge separation, and 3) oxygen generation, were realized for the first time by using the light‐harvesting PMO.     

Efficient Light‐Harvesting Systems with Tunable Emission through Controlled Precipitation in Confined Nanospace

Light harvesting is a key step in photosynthesis but creation of synthetic light‐harvesting systems (LHSs) with high efficiencies has been challenging. When donor and acceptor dyes with aggregation‐induced emission were trapped within the interior of cross‐linked reverse vesicles, LHSs were obtained readily through spontaneous hydrophobically driven aggregation of the dyes in water. Aggregation in the confined nanospace was critical to the energy transfer and the light‐harvesting efficiency. The efficiency of the excitation energy transfer (EET) reached 95 % at a donor/acceptor ratio of 100:1 and the energy transfer was clearly visible even at a donor/acceptor ratio of 10 000:1. Multicolor emission was achieved simply by tuning the donor/acceptor feed ratio in the preparation and the quantum yield of white light emission from the system was 0.38, the highest reported for organic materials in water to date.     

Ruthenium(II)–Polyimine–Coumarin Light‐Harvesting Molecular Arrays: Design Rationale and Application for Triplet–Triplet‐Annihilation‐Based Upconversion

Ru^II–bis‐pyridine complexes typically absorb below 450 nm in the UV spectrum and their molar extinction coefficients are only moderate (ε<16 000 M ^?1 cm^?1). Thus, Ru^II–polyimine complexes that show intense visible‐light absorptions are of great interest. However, no effective light‐harvesting ruthenium(II)/organic chromophore arrays have been reported. Herein, we report the first visible‐light‐harvesting Ru^II–coumarin arrays, which absorb at 475 nm (ε up to 63 300 M ^?1 cm^?1, 4‐fold higher than typical Ru^II–polyimine complexes). The donor excited state in these arrays is efficiently converted into an acceptor excited state (i.e., efficient energy‐transfer) without losses in the phosphorescence quantum yield of the acceptor. Based on steady‐state and time‐resolved spectroscopy and DFT calculations, we proposed a general rule for the design of Ru^II–polypyridine–chromophore light‐harvesting arrays, which states that the ¹IL energy level of the ligand must be close to the respective energy level of the metal‐to‐ligand charge‐transfer (M LCT) states. Lower energy levels of ¹IL/³IL than the corresponding ¹M LCT/³M LCT states frustrate the cascade energy‐transfer process and, as a result, the harvested light energy cannot be efficiently transferred to the acceptor. We have also demonstrated that the light‐harvesting effect can be used to improve the upconversion quantum yield to 15.2 % (with 9,10‐diphenylanthracene as a triplet‐acceptor/annihilator), compared to the parent complex without the coumarin subunit, which showed an upconversion quantum yield of only 0.95 %.     

Integrating DNA Photonic Wires into Light‐Harvesting Supramolecular Polymers

An approach combining DNA nanoscaffolds with supramolecular polymers for the efficient and directional propagation of light‐harvesting cascades has been developed. A series of photonic wires with different arrangements of fluorophores in DNA‐organized nanostructures were linked to light‐harvesting supramolecular phenanthrene polymers (SPs) in a self‐assembled fashion. Among them, a light‐harvesting complex (LHC) composed of SPs and a photonic wire of phenanthrene, Cy3, Cy5, and Cy5.5 chromophores reveals a remarkable energy transfer efficiency of 59 %. Stepwise transfer of the excitation energy collected by the light‐harvesting SPs via the intermediate Cy3 and Cy5 chromophores to the final Cy5.5 acceptor proceeds through a Förster resonance energy transfer mechanism. In addition, the light‐harvesting properties are documented by antenna effects ranging from 1.4 up to 23 for different LHCs.     

Long‐Distance Electronic Energy Transfer in Light‐Harvesting Supramolecular Polymers

The efficient collection of solar energy relies on the design and construction of well‐organized light‐harvesting systems. Herein we report that supramolecular phenanthrene polymers doped with pyrene are effective collectors of light energy. The linear polymers are formed through the assembly of short amphiphilic oligomers in water. Absorption of light by phenanthrene residues is followed by electronic energy transfer along the polymer over long distances (>100 nm) to the accepting pyrene molecules. The high efficiency of the energy transfer, which is documented by large fluorescence quantum yields, suggests a quantum coherent process.     

Cyclic Tetramers of Zinc Chlorophylls as a Coupled Light‐Harvesting Antenna–Charge‐Separation System

A coupled light‐harvesting antenna–charge‐separation system, consisting of self‐assembled zinc chlorophyll derivatives that incorporate an electron‐accepting unit, is reported. The cyclic tetramers that incorporated an electron acceptor were constructed by the co‐assembly of a pyridine‐appended zinc chlorophyll derivative, ZnPy , and a zinc chlorophyll derivative further decorated with a fullerene unit, ZnPyC₆₀ . Comprehensive steady‐state and time‐resolved spectroscopic studies were conducted for the individual tetramers of ZnPy and ZnPyC₆₀ as well as their co‐tetramers. Intra‐assembly singlet energy transfer was confirmed by singlet–singlet annihilation in the ZnPy tetramer. Electron transfer from the singlet chlorin unit to the fullerene unit was clearly demonstrated by the transient absorption of the fullerene radical anion in the ZnPyC₆₀ tetramer. Finally, with the co‐tetramer, a coupled light‐harvesting and charge‐separation system with practically 100 % quantum efficiency was demonstrated.     

Efficient calculation of open quantum system dynamics and time‐resolved spectroscopy with distributed memory HEOM (DM‐HEOM)

Time‐ and frequency‐resolved optical signals provide insights into the properties of light‐harvesting molecular complexes, including excitation energies, dipole strengths and orientations, as well as in the exciton energy flow through the complex. The hierarchical equations of motion (HEOM) provide a unifying theory, which allows one to study the combined effects of system‐environment dissipation and non‐Markovian memory without making restrictive assumptions about weak or strong couplings or separability of vibrational and electronic degrees of freedom. With increasing system size the exact solution of the open quantum system dynamics requires memory and compute resources beyond a single compute node. To overcome this barrier, we developed a scalable variant of HEOM. Our distributed memory HEOM, DM‐HEOM, is a universal tool for open quantum system dynamics. It is used to accurately compute all experimentally accessible time‐ and frequency‐resolved processes in light‐harvesting molecular complexes with arbitrary system‐environment couplings for a wide range of temperatures and complex sizes. © 2018 Wiley Periodicals, Inc.     

Enhanced Light‐Harvesting Capacity by Micellar Assembly of Free Accessory Chromophores and LH1‐like Antennas

Biohybrid light‐harvesting antennas are an emerging platform technology with versatile tailorability for solar‐energy conversion. These systems combine the proven peptide scaffold unit utilized for light harvesting by purple photosynthetic bacteria with attached synthetic chromophores to extend solar coverage beyond that of the natural systems. Herein, synthetic unattached chromophores are employed that partition into the organized milieu (e.g. detergent micelles) that house the LH1‐like biohybrid architectures. The synthetic chromophores include a hydrophobic boron‐dipyrrin dye (A1) and an amphiphilic bacteriochlorin (A2), which transfer energy with reasonable efficiency to the bacteriochlorophyll acceptor array (B875) of the LH1‐like cyclic oligomers. The energy‐transfer efficiencies are markedly increased upon covalent attachment of a bacteriochlorin (B1 or B2) to the peptide scaffold, where the latter likely acts as an energy‐transfer relay site for the (potentially diffusing) free chromophores. The efficiencies are consistent with a Förster (through‐space) mechanism for energy transfer. The overall energy‐transfer efficiency from the free chromophores via the relay to the target site can approach those obtained previously by relay‐assisted energy transfer from chromophores attached at distant sites on the peptides. Thus, the use of free accessory chromophores affords a simple design to enhance the overall light‐harvesting capacity of biohybrid LH1‐like architectures.     

Dephasing and Dissipation in a Source–Drain Model of Light‐Harvesting Systems

The energy transport process in natural‐light‐harvesting systems is investigated by solving the time‐dependent Schrödinger equation for a source–network–drain model incorporating the effects of dephasing and dissipation, owing to coupling with the environment. In this model, the network consists of electronically coupled chromophores, which can host energy excitations (excitons) and are connected to source channels, from which the excitons are generated, thereby simulating exciton creation from sunlight. After passing through the network, excitons are captured by the reaction centers and converted into chemical energy. In addition, excitons can reradiate in green plants as photoluminescent light or be destroyed by nonphotochemical quenching (NPQ). These annihilation processes are described in the model by outgoing channels, which allow the excitons to spread to infinity. Besides the photoluminescent reflection, the NPQ processes are the main outgoing channels accompanied by energy dissipation and dephasing. From the simulation of wave‐packet dynamics in a one‐dimensional chain, it is found that, without dephasing, the motion remains superdiffusive or ballistic, despite the strong energy dissipation. At an increased dephasing rate, the wave‐packet motion is found to switch from superdiffusive to diffusive in nature. When a steady energy flow is injected into a site of a linear chain, exciton dissipation along the chain, owing to photoluminescence and NPQ processes, is examined by using a model with coherent and incoherent outgoing channels. It is found that channel coherence leads to suppression of dissipation and multiexciton super‐radiance. With this method, the effects of NPQ and dephasing on energy transfer in the Fenna–Matthews–Olson complex are investigated. The NPQ process and the photochemical reflection are found to significantly reduce the energy‐transfer efficiency in the complex, whereas the dephasing process slightly enhances the efficiency. The calculated absorption spectrum reproduces the main features of the measured counterpart. As a comparison, the exciton dynamics are also studied in a linear chain of pigments and in a multiple‐ring system of light‐harvesting complexes II (LH2) from purple bacteria by using the Davydov D₁ ansatz. It is found that the exciton transport shows superdiffusion characteristics in both the chain and the LH2 rings.     

A Complex Comprising a Cyanine Dye Rotaxane and a Porphyrin Nanoring as a Model Light‐Harvesting System

A nanoring‐rotaxane supramolecular assembly with a Cy7 cyanine dye (hexamethylindotricarbocyanine) threaded along the axis of the nanoring was synthesized as a model for the energy transfer between the light‐harvesting complex LH1 and the reaction center in purple bacteria photosynthesis. The complex displays efficient energy transfer from the central cyanine dye to the surrounding zinc porphyrin nanoring. We present a theoretical model that reproduces the absorption spectrum of the nanoring and quantifies the excitonic coupling between the nanoring and the central dye, thereby explaining the efficient energy transfer and demonstrating similarity with structurally related natural light‐harvesting systems.     

Synthesis and Functional Reconstitution of Light‐Harvesting Complex II into Polymeric Membrane Architectures

One of most important processes in nature is the harvesting and dissipation of solar energy with the help of light‐harvesting complex II (LHCII). This protein, along with its associated pigments, is the main solar‐energy collector in higher plants. We aimed to generate stable, highly controllable, and sustainable polymer‐based membrane systems containing LHCII–pigment complexes ready for light harvesting. LHCII was produced by cell‐free protein synthesis based on wheat‐germ extract, and the successful integration of LHCII and its pigments into different membrane architectures was monitored. The unidirectionality of LHCII insertion was investigated by protease digestion assays. Fluorescence measurements indicated chlorophyll integration in the presence of LHCII in spherical as well as planar bilayer architectures. Surface plasmon enhanced fluorescence spectroscopy (SPFS) was used to reveal energy transfer from chlorophyll b to chlorophyll a, which indicates native folding of the LHCII proteins.