Artificial Photosystems Research Articles

Development of artificial photosystems based on designed proteins for mechanistic insights into photosynthesis.

This review aims to provide an overview of the progress in protein-based artificial photosystem design and their potential to uncover the underlying principles governing light-harvesting in photosynthesis. While significant advances have been made in this area, a gap persists in reviewing these advances. This review provides a perspective of the field, pinpointing knowledge gaps and unresolved challenges that warrant further inquiry. In particular, it delves into the key considerations when designing photosystems based on the chromophore and protein scaffold characteristics, presents the established strategies for artificial photosystems engineering with their advantages and disadvantages, and underscores the recent breakthroughs in understanding the molecular mechanisms governing light-harvesting, charge separation, and the role of the protein motions in the chromophore's excited state relaxation. By disseminating this knowledge, this article provides a foundational resource for defining the field of bio-hybrid photosystems and aims to inspire the continued exploration of artificial photosystems using protein design.

Identifying Root Origin of Insulating Polymer Mediated Solar Water Oxidation.

Rational construction of high-efficiency photoelectrodes with optimized carrier migration to the ideal active sites, is crucial for enhancing solar water oxidation. However, complexity in precisely modulating interface configuration and directional charge transfer pathways retards the design of robust and stable artificial photosystems. Herein, a straightforward yet effective strategy is developed for compact encapsulation of metal oxides (MOs) with an ultrathin non-conjugated polymer layer to modulate interfacial charge migration and separation. By periodically coating highly ordered TiO2 nanoarrays with oppositely charged polyelectrolyte of poly(dimethyl diallyl ammonium chloride) (PDDA), MOs/polymer composite photoanodes are readily fabricated under ambient conditions. It is verified that electrons photogenerated from the MOs substrate can be efficiently extracted by the ultrathin solid insulating PDDA layer, significantly boosting the carrier transport kinetics and enhancing charge separation of MOs, and thus triggering a remarkable enhancement in the solar water oxidation performance. The origins of the unexpected electron-withdrawing capability of such non-conjugated insulating polymer are unambiguously uncovered, and the scenario occurring at the interface of hybrid photoelectrodes is elucidated. The work would reinforce the fundamental understanding on the origins of generic charge transport capability of insulating polymer and benefit potential wide-spread utilization of insulating polymers as co-catalysts for solar energy conversion.

Precise Layer-by-Layer Assembly of Dual Quantum Dots Artificial Photosystems Enabling Solar Water Oxidation.

Quantum dots (QDs) colloidal nanocrystals are attracting enduring interest by scientific communities for solar energy conversion due to generic physicochemical merits including substantial light absorption coefficient, quantum confinement effect, enriched catalytically active sites, and tunable electronic structure. However, photo-induced charge carriers of QDs suffer from ultra-short charge lifespan and poor stability, rendering controllable vectorial charge modulation and customizing robust and stable QDs artificial photosystems challenging. Herein, tailor-made oppositely charged transition metal chalcogenides quantum dots (TMCs QDs) and MXene quantum dots (MQDs) are judiciously harnessed as the building blocks for electrostatic layer-by-layer assembly buildup on the metal oxides (MOs) framework. In these exquisitely designed LbL assembles MOs/(TMCs QDs/MQDs)n heterostructured photoanodes, TMCs QDs layer acts as light-harvesting antennas, and MQDs layer serves as electron-capturing mediator to relay cascade electrons from TMCs QDs to the MOs substrate, thereby yielding the spatially ordered tandem charge transport chain and contributing to the significantly boosted charge separation over TMCs QDs and solar water oxidation efficiency of MOs/(TMCs QDs/MQDs)n photoanodes. The relationship between interface configuration and charge transfer characteristics is unambiguously unlocked, by which photoelectrochemical mechanism is elucidated. This work would provide inspiring ideas for precisely mediating interfacial charge transfer pathways over QDs toward solar energy conversion.

Combined Covalent and Supramolecular Polymerization to Reinforce Perylenebisimide Photosynthetic "Quantasomes".

PSII-inspired quantasomes have emerged as promising artificial photosystems evolving oxygen from water due to their integrated multi-chromophore asset, hierarchical architecture, and efficient light-harvesting capabilities. In this study, we adopt a combined covalent and supramolecular strategy by implementing a poly-styrene backbone that reinforces proximity and pairing between adjacent perylenebisimide (PBI) quantasome units. The covalent fixation of the quantasome network results in a significant enhancement of the photoelectrocatalytic performance on engineered IO-ITO photoanodes, with up to 290 % photocurrent increase (J up to 100 μA cm-2, λ >450 nm, applied bias <1.23 V vs RHE, F.E.O2 >80 %) compared to the non-polymerized analog. Moreover, the direct PBI-quantasome polymerization on the photoanode surface was performed by light irradiation of the radical initiator 2,2'-Azobis(2-methylpropionamidine), improving the photoelectrode robustness under high solar irradiance (>8 suns) and limiting the photocurrent loss (<20 %) at 1.52 V vs RHE compared to the non-polymerized system.

Unraveling quantum coherences mediating primary charge transfer processes in photosystem II reaction center.

Photosystem II (PSII) reaction center (RC) is a unique complex that is capable of efficiently separating electronic charges across the membrane. The primary energy- and charge-transfer (CT) processes occur on comparable ultrafast timescales, which makes it extremely challenging to understand the fundamental mechanism responsible for the near-unity quantum efficiency of the transfer. Here, we elucidate the role of quantum coherences in the ultrafast energy and CT in the PSII RC by performing two-dimensional (2D) electronic spectroscopy at the cryogenic temperature of 20 kelvin, which captures the distinct underlying quantum coherences. Specifically, we uncover the electronic and vibrational coherences along with their lifetimes during the primary ultrafast processes of energy and CT. We construct an excitonic model that provides evidence for coherent energy and CT at low temperature in the 2D electronic spectra. The principles could provide valuable guidelines for creating artificial photosystems with exploitation of system-bath coupling and control of coherences to optimize the photon conversion efficiency to specific functions.

Photocarrier tunneling triggering CO2 photocatalysis.

Solar CO2 reduction to renewable hydrocarbon fuels offers a promising pathway to carbon neutrality, but it is retarded by tough CO2 activation, complicated mechanisms, sluggish charge transport kinetics, and a scarcity of strategies for precise tuning of charge transport pathways. Herein, we first conceptually design a novel insulating polymer-mediated electron-tunneling artificial photosystem via progressive interface configuration regulation, wherein tailor-made Ag@citrate nanocrystals (NCs) are controllably self-assembled on transition metal chalcogenides (TMCs) assisted by an ultrathin insulating polymer interim layer, i.e., poly(allylamine hydrochloride) (PAH). In this multilayered nano-architecture, a solid ultra-thin insulating PAH interim layer serves as an unexpected charge tunneling mediator to stimulate smooth electron transfer from the TMC substrate to the terminal electron reservoirs of Ag@citrate NCs, engendering the tandem charge transfer route and significantly boosting the visible-light-driven photocatalytic CO2-to-syngas conversion performances. Furthermore, we have ascertained that such TMC-insulating polymer-metal NC tunneling photosystems are universal. This study would spark new inspiration for unleashing the long-term neglected charge tunneling capability of insulating polymers and diversifying non-conjugated polymer-based artificial photosystems for solar-to-fuel energy conversion.

Customizing dumbbell-shaped heterostructured artificial photosystems steering versatile photoredox catalysis.

Benefiting from their excellent light-capturing ability, suitable energy band structure and abundant active sites, transition metal chalcogenides (TMCs) have been attracting widespread attention in heterogeneous photocatalysis. Nonetheless, TMCs still suffer from sluggish charge transfer kinetics, a rapid charge recombination rate and poor stability, rendering the construction of high-performance artificial photosystems challenging. Here, a ternary dumbbell-shaped CdS/MoS2/CuS heterostructure with spatially separated catalytically active sites has been elaborately designed. In such a heterostructured nanoarchitecture, MoS2 clusters, selectively grown on both ends of the CdS nanowires (NWs), act as terminal electron collectors, while CuS nanolayers, coated on the sidewalls of CdS NWs through ion exchange, form a P-N heterojunction with the CdS NW framework, which accelerates the migration of holes from CdS to CuS, effectively suppressing the oxidation of sulfide ions and improving the stability of CdS NWs. The well-defined dumbbell-shaped CdS/MoS2/CuS ternary heterostructure provides a structural basis for spatially precise regulation of the charge migration pathway, where photogenerated electrons and holes directionally migrate to the MoS2 and CuS catalytic sites, respectively, ultimately achieving efficient carrier separation and significantly enhancing photoactivity for both photocatalytic hydrogen generation and selective organic transformation under visible light. Moreover, we have also ascertained that such ion exchange and interface configuration engineering strategies are universal. Our work features a simple yet efficient strategy for smartly designing multi-component heterostructures to precisely modulate spatially vectorial charge separation at the nanoscale for solar-to-hydrogen conversion.

Controlled electron transfer by molecular wires embedded in ultrathin insulating membranes for driving redox catalysis.

Organic bilayers or amorphous silica films of a few nanometer thickness featuring embedded molecular wires offer opportunities for chemically separating while at the same time electronically connecting photo- or electrocatalytic components. Such ultrathin membranes enable the integration of components for which direct coupling is not sufficiently efficient or stable. Photoelectrocatalytic systems for the generation or utilization of renewable energy are among the most prominent ones for which ultrathin separation layers open up new approaches for component integration for improving efficiency. Recent advances in the assembly and spectroscopic, microscopic, and photoelectrochemical characterization have enabled the systematic optimization of the structure, energetics, and density of embedded molecular wires for maximum charge transfer efficiency. The progress enables interfacial designs for the nanoscale integration of the incompatible oxidation and reduction catalysis environments of artificial photosystems and of microbial (or biomolecular)-abiotic systems for renewable energy.

Filling the Gap: Atomically Precise Metal Nanoclusters‐Induced Z‐Scheme Photosystem toward Robust and Stable Solar Hydrogen Generation

AbstractAtomically precise metal nanoclusters (NCs) represent a promising generation of metal nanomaterial because of characteristic atomic stacking mode, abundant catalytic active sites, and molecular‐like discrete energy band structure. However, crafting metal NCs‐dominated photocatalytic systems with mediated charge transport pathways for photoredox catalysis is in the infant stage and their photocatalytic mechanisms remain elusive, which is largely hampered by the ultra‐short charge lifetime, generic instability, and complicated electronic structure of metal NCs. In this study, the smart construction of all‐solid‐state metal NCs‐transition metal chalcogenides quantum dots (TMCs QDs) Z‐scheme artificial photosystems for robust and stable solar‐to‐hydrogen conversion is demonstrated. The concurrent favorable photosensitization efficiency of metal NCs and TMCs QDs synergistically stimulate the unexpected Z‐scheme charge transport pathway, which significantly boosts the anisotropic spatial vectorial charge transport/separation, giving rise to considerably enhanced visible‐light‐responsive photocatalytic hydrogen generation performances along with favorable stability. This study would push forward the prosperity of exploring metal NCs‐based photosystems for solar‐to‐hydrogen conversion.

Tandem architectures for artificial thylakoid membranes

In this concept paper, new layered materials, such as multilayer hybrid systems, are described. These materials can be implemented into novel biomimetic devices, which can act as artificial photosystems or as “artificial thylakoid membranes” e.g. for the splitting of water. The architecture can be based on active nanoparticles or small catalytic clusters which can be synthesized from robust, inexpensive, and abundant material precursors. These multi-layered architectures can act as “artificial thylakoid membranes”, which can mimic the photosynthetic apparatus on the nanoscale. The development of “artificial thylakoid membranes” and tandem devices promises a strong impact and benefits for the field of artificial photosynthesis and the development of artificial leaves.

Defect Engineering in 0D/2D S-Scheme Heterojunction Photocatalysts for Water Activation: Synergistic Roles of Nickel Doping and Oxygen Vacancy.

Photocatalytic hydrodechlorination (HDC) is a promising method for eliminating chlorinated organic compounds (COCs) from water, but it requires catalysts with excellent water activation ability. Defect engineering is a feasible way to enhance the catalytic performance of photocatalysts by improving light adsorption, charge carrier dynamics, and surface reactions. Herein, a well-designed 0D/2D S-scheme heterojunction with favorable band structures and defective interfaces was constructed via defect tailoring on TiO2 quantum dots (QDs) and the interface structure. The optimized catalyst Ni-TiO2-x/g-C3N4 with 1% Ni doping after thermal treatment at 300 °C under nitrogen resulted in superior visible-light-driven activity in trichloroethylene (TCE) photocatalytic HDC, approximately an 18.2-fold increase as compared with g-C3N4. Ni doping and thermal-induced oxygen vacancies were verified to synergistically endow the catalyst with improved visible-light absorption efficiency, ameliorated charge separation and migration, and enhanced redox potential. Experimental and theoretical results showed that the synergy of multifold defects in promoting visible-light harvesting was mainly due to the characteristic multiple midgap states, in terms of different intermediate energy levels and narrowed bandgap. Furthermore, the contradicting effects of midgap states on photogenerated charge carrier dynamics were mediated by the defective S-scheme heterojunction, where the detrimental charge recombination relating to excessive defects was considerably inhibited via superior spatial charge separation and promoted surface redox reactions. The design of defect-engineered heterojunctions and the role of controlled defects in adjusting band structures provide valuable insights for creating highly efficient artificial photosystems in the visible region.

Confinement of Pyridine Derivatives into a Metal-Organic Framework Host as Electron Acceptors to Achieve Photoinduced Electron-Transfer.

The photoinduced electron-transfer (ET) process plays an irreplaceable role in chemical and biological fields exemplified by enzymatic catalysis, artificial photosystems, solar energy conversion, and so forth. Searching for a new photoinduced ET system is of great importance for the development of functional materials. Herein, a series of host-guest compounds based on a magnesium metal-organic framework (Mg-MOF) as a host and pyridine derivatives as guests have been presented. Notably, strong O-H···N hydrogen bond between the oxygen atom of μ2-H2O and the nitrogen atom of pyridine enables proton delocalization between water molecule and pyridine guest. Despite the absence of photochromic modules in these host-guest compounds, long-lived charge-separated states with distinct color changes can be formed after UV-light irradiation. The substituents in pyridines and the proton delocalization ability between the host and guests have a great influence on their photoinduced ET process to endow the MOF materials with tunable photoinduced charge-separated states.

Bio-inspired high-efficiency photosystem by synergistic effects of core-shell structured Au@CdS nanoparticles and their engineered location on {001} facets of SrTiO3 nanocrystals

Natural photosynthesis, which provides a green and high-efficiency energy conversion path by spatial separation of photogenerated carriers through combined actions of molecules ingeniously arranged in an efficient solar nanospace, highlights the importance of rational nanostructure design to realize artificial high-efficiency photosystem. Inspired by these unique features, we constructed a high-efficiency ternary photosystem by selectively decorating the {001} facets of 18-facet SrTiO 3 with Au@CdS photosensitizers via a green photo-assisted method. Benefiting from the dual-facilitated charge carriers transportation in core-shell structured Au@CdS heterojunction and well-faceted 18-facet SrTiO 3 nanocrystal, such a photocatalyst could realize the effective spatial separation of photogenerated electrons and holes. As expected, the 18-facet SrTiO 3 /Au@CdS photocatalyst exhibits superior activity in visible-light-driven photocatalytic hydrogen evolution (4.61 mmol h −1 g −1 ), 166% improvement in comparison with randomly deposited Au@CdS (1.73 mmol h −1 g −1 ). This work offers new insight into the development of green and high-efficiency photocatalytic systems based on the rational nanostructure design by crystal facet engineering.

Ultrathin electron and proton-conducting membranes for nanoscale integrated artificial photosystems

Ultrathin separation membranes of ten nanometer thickness capable of separating small molecules for avoiding back reactions while providing adequate electron and proton transport enable the development of nanoscale integrated artificial photosystems.

Merging molecular catalysts and metal-organic frameworks for photocatalytic fuel production.

In the effort to generate sustainable clean energy from abundant resources such as water and carbon dioxide, solar fuel production-the combination of solar-light harvesting and the generation of efficient chemical energy carriers-by artificial molecular photosystems is very attractive. Molecular constituents that display attractive features for chemical energy conversion (such as high product selectivity and atom economy) have been developed, and their interfacing with host materials has enabled recyclability, controlled site positioning, as well as access to fundamental insights into the catalytic mechanism and environment-governed selectivity. Among the wide variety of supports, metal-organic frameworks (MOFs) possess valuable characteristics (such as their porosity and versatility) that can influence the reaction environment and material architecture in a unique fashion. Here we highlight the various existing synthetic strategies to graft molecular complexes such as catalysts and photosensitizers onto MOFs for solar fuel production. The opportunities and limitations of one-pot and stepwise approaches are critically assessed, and the resulting materials are discussed based on their photocatalytic performances and the practical applicability of selected examples.

An Artificial Photosystem of Metal-Insulator-CTF Nanoarchitectures for Highly Efficient and Selective CO2 Conversion to CO.

It is of pivotal significance to explore robust photocatalysts to promote the photoreduction of CO2 into solar fuels. Herein, an intelligent metal-insulator-semiconductor (MIS) nano-architectural photosystem was constructed by electrostatic self-assembly between cetyltrimethylammonium bromide (CTAB) insulator-capped metal Ni nanoparticles (NPs) and covalent triazine-based frameworks (CTF-1). The metal-insulator-CTF composites unveiled a substantially higher CO evolution rate (1254.15 μmol g-1 h-1 ) compared with primitive CTF-1 (1.08 μmol g-1 h-1 ) and reached considerable selectivity (98.9 %) under visible-light irradiation. The superior photocatalytic CO2 conversion activity over Ni-CTAB-CTF nanoarchitecture could be attributed to the larger surface area, reinforced visible-light response, and CO2 capture capacity. More importantly, the Ni-CTAB-CTF nanoarchitecture endowed the photoexcited electrons on CTF-1 with the ability to tunnel across the thin CTAB insulating layer, directionally migrating to Ni NPs and thereby leading to the efficient separation of photogenerated electrons and holes in the photosystem. In addition, isotope-labeled (13 CO2 ) tracer results verified that the reduction products come from CO2 rather than the decomposition of the photocatalysts. This study opens a new avenue for establishing a highly efficient and selective artificial photosystem for CO2 conversion.

Molecular design strategy for realizing vectorial electron transfer in photoelectrodes

<h2>Summary</h2> Vectorial electron transfer is essential for developing ideal artificial photosystems. Conventional photosensitizers with only strong electronic coupling, as used in photovoltaics, cannot achieve vectorial electron transfer because of their rapid charge recombination. Herein, we present a design strategy for integrating strong (∼600 cm⁻¹) and relatively weak (310 cm⁻¹) electronic coupling in a single molecule to realize vectorial electron transfer in dye-sensitized solar cells. Four sensitizers with donor-acceptor-π-spacer and anchoring group configurations are developed, and the electronic coupling in these sensitizers is controlled by the π-spacers of varying steric hindrances. Transient-absorption spectroscopies reveal the occurrence of vectorial electron transfer in the designed sensitizer by suppressing charge recombination via weakened electronic coupling between the acceptor and π-spacer and the efficient charge injection via strong electronic coupling between the donor and acceptor. The optimization of electronic coupling in the sensitizers improves the photovoltaic performances, achieving a power-conversion efficiency of 10.8%.

Vacancy-defect semiconductor quantum dots induced an S-scheme charge transfer pathway in 0D/2D structures under visible-light irradiation

Designing heterojunctions with a feasible charge transfer pathway is a promising strategy for establishing highly efficient artificial photosystems. The step-scheme (S-scheme) heterojunction has shown considerable potential in enhancing redox ability and charge transfer of photocatalysts. Herein, a hierarchical heterojunction involving vacancy-defect TiO2 quantum dots (QDs) and 2D g-C3N4 nanosheets was constructed using a multi-step assembly strategy. Computational and experimental studies show that the vacancy-defect TiO2 QDs can induce an S-scheme charge transfer pathway in the 0D/2D heterojunction under visible-light irradiation, which greatly improved the redox ability of charge carriers, enhanced the charge transfer and separation at interfaces, and facilitated the H2O adsorption and dissociation. This results in over 10-fold increase in hydrogen evolution reaction (HER) of photocatalytic water splitting for a wide range of carbon nitrides. The values achieved compare favorably with the best carbon nitride photocatalysts developed to date.

Biocatalytic conversion of sunlight and carbon dioxide to solar fuels and chemicals.

This review discusses the progress in the assembly of photosynthetic biohybrid systems using enzymes and microbes as the biocatalysts which are capable of utilising light to reduce carbon dioxide to solar fuels. We begin by outlining natural photosynthesis, an inspired biomachinery to develop artificial photosystems, and the rationale and motivation to advance and introduce biological substrates to create more novel, and efficient, photosystems. The case studies of various approaches to the development of CO2-reducing microbial semi-artificial photosystems are also summarised, showcasing a variety of methods for hybrid microbial photosystems and their potential. Finally, approaches to investigate the relatively ambiguous electron transfer mechanisms in such photosystems are discussed through the presentation of spectroscopic techniques, eventually leading to what this will mean for the future of microbial hybrid photosystems.

Polymer‐Mediated Electron Tunneling Towards Solar Water Oxidation

AbstractExploiting emerging artificial photosystems with regulated vectorial charge transfer pathways is retarded by the difficulties in precise interface modulation at the nanoscale level, deficiency of suitable assembly methodologies, and ultra‐short charge lifetime. Herein, it is first conceptually demonstrated the general design of transition metal chalcogenides quantum dots (TMCs QDs)‐insulating polymer‐metal oxides (MOs) electron‐tunneling photosystems, wherein TMCs QDs are controllably layer‐by‐layer self‐assembled on the MOs substrates assisted by an ultrathin insulating polymer interim layer. It is ascertained that electrons photoexcited over TMCs QDs in spatially highly ordered MOs/(TMCs QDs/polymer)n multilayered heterostructures can be unidirectionally extracted and tunneled to the MOs substrates across the intermediate insulating polymer layer by engendering the tandem charge transfer to accelerate the interfacial charge migration kinetics, thereby triggering the significantly boosted net efficiency of solar‐driven photoelectrochemical water oxidation. This study would spark new inspirations for designing novel electron‐tunneling photosystems for fine carrier modulation towards solar energy harvesting and conversion.