Artificial Antenna Systems Research Articles

A stimuli responsive lanthanide-based hydrogel possessing tunable luminescence by efficient energy transfer pathways

Energy transfer as an important component in light-harvesting antenna systems can mimic effectively natural photosynthesis processes, showing great potential in optoelectronic devices. Herein, we report a responsive polymeric hydrogel based on the combination of excited state intramolecular proton transfer (ESIPT) molecule (Salicylic acid, Sal) and terbium (III) (Tb3+), as enabled by external stimuli to construct artificial light-harvesting antenna systems. Benefiting from unique photophysical properties of Sal, the synthesized hydrogel displays a temperature-dependent reversible opaque ↔ transparent states transition, accompanied with an interesting photoluminescence behavior. Moreover, by further incorporating europium (III) (Eu3+) into the hydrogel, we demonstrate well-defined cascades of energy transfer that provides a tunable optical output from the collection of lanthanides by the excitation of a common sensitizer (Sal) upon base vapor stimulation. Efficient energy transfer efficiency from Tb3+ to Eu3+, as high as 97.8%, was also obtained as established by the time-resolved fluorescence spectroscopy analysis.

Energy transduction through FRET in self-assembled soft nanostructures based on surfactants/polymers: current scenario and prospects.

The self-assembled systems of surfactants/polymers, which are capable of supporting energy funneling between fluorophores, have recently gained significant attraction. Surfactant and polymeric micelles form nanoscale structures spanning a radius of 2-10 nm are generally suitable for the transduction of energy among fluorophores. These systems have shown great potential in Förster resonance energy transfer (FRET) due to their unique characteristics of being aqueous based, tendency to remain self-assembled, spontaneous formation, tunable nature, and responsiveness to different external stimuli. This review presents current developments in the field of energy transfer, particularly the multi-step FRET processes in the self-assembled nanostructures of surfactants/polymers. The part one of this review presents a background and brief overview of soft systems and discusses certain aspects of the self-assemblies of surfactants/polymers and their co-solubilization property to bring fluorophores to close proximity to transduce energy. The second part of this review deals with single-step and multi-step FRET in the self-assemblies of surfactants/polymers and links FRET systems with advanced smart technologies including multicolor formation, data encryption, and artificial antenna systems. This review also discusses the diverse examples in the literature to present the emerging applications of FRET. Finally, the prospects regarding further improvement of FRET in self-assembled soft systems are outlined.

Microwave assisted synthesis of boron and nitrogen rich graphitic quantum dots to enhance fluorescence of photosynthetic pigments

Energy transfer between quantum dots and biomolecules is of interest due to high absorption capacity and high quantum efficiency of quantum dots. Amongst all types of quantum dots, graphene and graphitic quantum dots have great potential for energy transfer studies due to their high biocompatibility and low toxicity. In this study, a simple route to synthesize boron and nitrogen rich graphitic quantum dots (C-BN) and boron carbon nitride (BCN) quantum dots is demonstrated. Quantum dots were synthesized in a domestic microwave oven. Composition of quantum dots was controlled by tuning initial mole ratio of boron and nitrogen precursors. As molar ratio of boron precursor was increased, formation of C-BN quantum dots was favoured. C-BN quantum dots were mainly composed of boron and nitrogen (with around 10 % carbon) in their main composition, and sized around 2 nm with bright photoluminescence. To the best of our knowledge, this is the first study which proposes a bottom-up synthesis method to synthesize C-BN quantum dots based on domestic microwaves. Also, treating photosynthetic pigments with quantum dots resulted in 20 % enhancement of fluorescence of photosynthetic pigments at 670 nm, which demonstrates that C-BN and BCN quantum dots can be important constituents of artificial antenna systems for photosynthetic organisms.

Light polarization dependency existing in the biological photosystem and possible implications for artificial antenna systems.

The processes of biological photosynthesis provide inspiration and valuable lessons for artificial energy collection, transfer, and conversion systems. The extraordinary efficiency of each sequential process of light to biomass conversion originates from the unique architecture and mechanism of photosynthetic proteins. Near 100% quantum efficiency of energy transfer in biological photosystems is achieved by the chlorophyll assemblies in antenna complexes, which also exhibit a significant degree of light polarization. The three-dimensional chiral assembly of chlorophylls is an optimized biological architecture that enables maximum energy transfer efficiency with precisely designed coupling between chlorophylls. In this review, we summarize the key lessons from the photosynthetic processes in biological photosystems, and move our focus to energy transfer mechanisms and the chiral structure of the chlorophyll assembly. Then, we introduce recent approaches and possible implications to realize the biological energy transfer processes on bioinspired scaffold-based artificial antenna systems.

Photophysical behavior of systematically substituted (di-2-pyridylaminomethyl) benzene ligands and its Re(I) complexes: A combined experimental and theoretical approach

Abstract The photophysical behavior of a series of flexible di-2-pyridylaminomethyl substituted ligands systematically substituted on a rigid benzene core and their corresponding mono-metallic Re(I) complexes have been investigated by steady state and time-resolved fluorescence spectroscopy in different composition of DMSO–water binary solvent mixtures. Unusual fluorescence properties in lower DMSO content ( X DMSO = 0.1–0.3) solvent mixtures is consistent with fascinating property of DMSO, which is known to perturb the hydrogen bonding ability of water with the solute. Spin allowed inter-ligand π–π * transition is more apparent in (1, 3) substituted systems. The calculated spectroscopic parameters of the complexes are significantly different from the ligands, mainly due to ligand to metal charge transfer. The experimental observations are in very good agreement with the theoretical results obtained at B3LYP/6-31G(d,p)/LANL2DZ level of density functional theory (DFT) calculation. Natural bond orbital (NBO) analysis and examination of frontier molecular orbitals reveal that the basic architecture of the symmetrically substituted multi-chromophoric ligand can induce excitation energy hopping, similar to an artificial antenna system.

Coherent electronic and nuclear dynamics in a rhodamine heterodimer-DNA supramolecular complex.

Elucidating the role of quantum coherences in energy migration within biological and artificial multichromophoric antenna systems is the subject of an intense debate. It is also a practical matter because of the decisive implications for understanding the biological processes and engineering artificial materials for solar energy harvesting. A supramolecular rhodamine heterodimer on a DNA scaffold was suitably engineered to mimic the basic donor-acceptor unit of light-harvesting antennas. Ultrafast 2D electronic spectroscopic measurements allowed identifying clear features attributable to a coherent superposition of dimer electronic and vibrational states contributing to the coherent electronic charge beating between the donor and the acceptor. The frequency of electronic charge beating is found to be 970 cm-1 (34 fs) and can be observed for 150 fs. Through the support of high level ab initio TD-DFT computations of the entire dimer, we established that the vibrational modes preferentially optically accessed do not drive subsequent coupling between the electronic states on the 600 fs of the experiment. It was thereby possible to characterize the time scales of the early time femtosecond dynamics of the electronic coherence built by the optical excitation in a large rigid supramolecular system at a room temperature in solution.

Supramolecular architectures featuring the antenna effect in solid state DSSCs

Hybrid artificial antenna systems, with implementation of nature's basic concept of self-organization of chromophores, have been prepared and investigated in DSSCs. .

Supramolecular Organization of Dye Molecules in Zeolite L Channels: Synthesis, Properties, and Composite Materials.

Sequential insertion of different dyes into the 1D channels of zeolite L (ZL) leads to supramolecular sandwich structures and allows the formation of sophisticated antenna composites for light harvesting, transport, and trapping. The synthesis and properties of dye molecules, host materials, composites, and composites embedded in polymer matrices, including two- and three-color antenna systems, are described. Perylene diimide (PDI) dyes are an important class of chromophores and are of great interest for the synthesis of artificial antenna systems. They are especially well suited to advancing our understanding of the structure-transport relationship in ZL because their core fits tightly through the 12-ring channel opening. The substituents at both ends of the PDIs can be varied to a large extent without influencing their electronic absorption and fluorescence spectra. The intercalation/insertion of 17 PDIs, 2 terrylenes, and 1 quaterrylene into ZL are compared and their interactions with the inner surface of the ZL nanochannels discussed. ZL crystals of about 500 nm in size have been used because they meet the criteria that must be respected for the preparation of antenna composites for light harvesting, transport, and trapping. The photostability of dyes is considerably improved by inserting them into the ZL channels because the guests are protected by being confined. Plugging the channel entrances, so that the guests cannot escape into the environment is a prerequisite for achieving long-term stability of composites embedded in an organic matrix. Successful methods to achieve this goal are described. Finally, the embedding of dye-ZL composites in polymer matrices, while maintaining optical transparency, is reported. These results facilitate the rational design of advanced dye-zeolite composite materials and provide powerful tools for further developing and understanding artificial antenna systems, which are among the most fascinating subjects of current photochemistry and photophysics.

Light-Activated Photo Protection in an Artificial Antenna System

Inspired by photosynthetic mechanisms in natural system, we introduced a light-sensitive photo protective quenching element in a DNA-templated artificial antenna model to control the flow of energy as a function of light intensity excitation. The Orange Carotenoid Protein (OCP) is a non-photochemical quencher in cyanobacteria: under high light conditions the protein undergoes a spectral shift, and by binding to the Phycobilisome it absorbs excess light and dissipates it as heat. By using DNA as a scaffold, we constructed an antenna system made of organic dyes (Cy3, Cy5), and we assembled OCP on it as a modulated quenching element. Controlling the light intensity shined on the sample allows us to switch the direction of the energy flow from the green label Cy3 to either Cy5, under low light conditions, or to OCP, under intense illumination. We show the construction, spectroscopic characterization and working principle of this system. The results presented here open exciting possibilities in the engineering of complex, regulated pathways in artificial light harvesting systems.

Fluorescence polarization measures energy funneling in single light-harvesting antennas--LH2 vs conjugated polymers.

Numerous approaches have been proposed to mimic natural photosynthesis using artificial antenna systems, such as conjugated polymers (CPs), dendrimers, and J-aggregates. As a result, there is a need to characterize and compare the excitation energy transfer (EET) properties of various natural and artificial antennas. Here we experimentally show that EET in single antennas can be characterized by 2D polarization imaging using the single funnel approximation. This methodology addresses the ability of an individual antenna to transfer its absorbed energy towards a single pool of emissive states, using a single parameter called energy funneling efficiency (ε). We studied individual peripheral antennas of purple bacteria (LH2) and single CP chains of 20 nm length. As expected from a perfect antenna, LH2s showed funneling efficiencies close to unity. In contrast, CPs showed lower average funneling efficiencies, greatly varying from molecule to molecule. Cyclodextrin insulation of the conjugated backbone improves EET, increasing the fraction of CPs possessing ε = 1. Comparison between LH2s and CPs shows the importance of the protection systems and the protein scaffold of LH2, which keep the chromophores in functional form and at such geometrical arrangement that ensures excellent EET.

ChemInform Abstract: The Importance of Various Anchoring Groups Attached on Porphyrins as Potential Dyes for DSSC Applications

AbstractReview: 124 refs.

Reengineering the Optical Absorption Cross-Section of Photosynthetic Reaction Centers

Engineered cysteine residues near the primary electron donor (P) of the reaction center from the purple photosynthetic bacterium Rhodobacter sphaeroides were covalently conjugated to each of several dye molecules in order to explore the geometric design and spectral requirements for energy transfer between an artificial antenna system and the reaction center. An average of 2.5 fluorescent dye molecules were attached at specific locations near P. The enhanced absorbance cross-section afforded by conjugation of Alexa Fluor 660 dyes resulted in a 2.2-fold increase in the formation of reaction center charge-separated state upon intensity-limited excitation at 650 nm. The effective increase in absorbance cross-section resulting from the conjugation of two other dyes, Alexa Fluor 647 and Alexa Fluor 750, was also investigated. The key parameters that dictate the efficiency of dye-to-reaction center energy transfer and subsequent charge separation were examined using both steady-state and time-resolved fluorescence spectroscopy as well as transient absorbance spectroscopy techniques. An understanding of these parameters is an important first step toward developing more complex model light-harvesting systems integrated with reaction centers.

Hierarchical Self-Assembly of a Biomimetic Light-Harvesting Antenna Based on DNA G-Quadruplexes

A new modular approach to an artificial light-harvesting antenna system is presented. The approach involves the hierarchical self-assembly of porphyrin acceptor molecules to G-quadruplexes tethered to coumarin donor moieties.

Artificial light-harvesting antenna systems grafted on a carbohydrate platform

An enantiopure α-D-glucopyranoside derivative has been used as a platform to prepare artificial antenna systems based on bodipy subunits. Efficient and ultrafast energy transfer (in the fs and ps time regimes) takes place in the multibodipy systems.

Förster Resonance Energy Transfer in Quantum Dot–Dye‐Loaded Zeolite L Nanoassemblies

AbstractNanoassemblies formed by coating a dye‐loaded zeolite L surface with CdSe/ZnS core/shell quantum dots (QDs) is described. A photoinduced energy transfer is observed from the excited QDs, which are on the surface of the zeolite crystals, to dye molecules (energy acceptors) encapsulated and aligned in the 1D channels of the aluminosilicate host. Steady‐state and time‐resolved spectroscopy and microscopy are used to quantify the Förster resonance energy transfer occurring through electronic transition dipole interactions between the QDs and the oxonine‐loaded zeolite L crystals. For the first time the energy transfer in artificial antenna systems based on quantum dots and molecules hosted in inert systems is described.

Designing Dye–Nanochannel Antenna Hybrid Materials for Light Harvesting, Transport and Trapping

We discuss artificial photonic antenna systems that are built by incorporating chromophores into one-dimensional nanochannel materials and by organizing the latter in specific ways. Zeolite L (ZL) is an excellent host for the supramolecular organization of different kinds of molecules and complexes. The range of possibilities for filling its one-dimensional channels with suitable guests has been shown to be much larger than one might expect. Geometrical constraints imposed by the host structure lead to supramolecular organization of the guests in the channels. The arrangement of dyes inside the ZL channels is what we call the first stage of organization. It allows light harvesting within the volume of a dye-loaded ZL crystal and also the radiationless transport of energy to either the channel ends or center. One-dimensional FRET transport can be realized in these guest-host materials. The second stage of organization is realized by coupling either an external acceptor or donor stopcock fluorophore at the ends of the ZL channels, which can then trap or inject electronic excitation energy. The third stage of organization is obtained by interfacing the material to an external device via a stopcock intermediate. A possibility to achieve higher levels of organization is by controlled assembly of the host into ordered structures and preparation of monodirectional materials. The usually strong light scattering of ZL can be suppressed by refractive-index matching and avoidance of microphase separation in hybrid polymer/dye-ZL materials. The concepts are illustrated and discussed in detail on a bidirectional dye antenna system. Experimental results of two materials with a donor-to-acceptor ratio of 33:1 and 52:1, respectively, and a three-dye system illustrate the validity and challenges of this approach for synthesizing dye-nanochannel hybrid materials for light harvesting, transport, and trapping.

Photosynthetic Light-Harvesting Is Tuned by the Heterogeneous Polarizable Environment of the Protein

In photosynthesis, special antenna proteins that contain multiple light-absorbing molecules (chromophores) are able to capture sunlight and transfer the excitation energy to reaction centers with almost 100% quantum efficiencies. The critical role of the protein scaffold in holding the appropriate arrangement of the chromophores is well established and can be intuitively understood given the need to keep optimal dipole-dipole interactions between the energy-transferring chromophores, as described by Förster theory more than 60 years ago. However, the question whether the protein structure can also play an active role by tuning such dipole-dipole interactions has not been answered so far, its effect being rather crudely described by simple screening factors related to the refractive index properties of the system. Here, we present a combined quantum chemical/molecular mechanical approach to compute electronic couplings that accounts for the heterogeneous dielectric nature of the protein-solvent environment in atomic detail. We apply the method to study the effect of dielectric heterogeneity in the energy migration properties of the PE545 principal light-harvesting antenna of the cryptomonad Rhodomonas CS24. We find that dielectric heterogeneity can profoundly tune by a factor up to ∼4 the energy migration rates between chromophore sites compared to the average continuum dielectric view that has historically been assumed. Our results indicate that engineering of the local dielectric environment can potentially be used to optimize artificial light-harvesting antenna systems.

Selective Assembly of Photosynthetic Antenna Proteins into a Domain-Structured Lipid Bilayer for the Construction of Artificial Photosynthetic Antenna Systems: Structural Analysis of the Assembly Using Surface Plasmon Resonance and Atomic Force Microscopy

Two types of photosynthetic membrane proteins, the peripheral antenna complex (LH2) and the core antenna/reaction center complex (LH1-RC), play an essential role in the primary process of purple bacterial photosynthesis, that is, capturing light energy, transferring it to the RC where it is used in subsequent charge separation. Establishment of experimental platforms is required to understand the function of the supramolecular assembly of LH2 and LH1-RC molecules into arrays. In this study, we assembled LH2 and LH1-RC arrays into domain-structured planar lipid bilayers placed on a coverglass using stepwise combinations of vesicle-to-planar membrane formation and vesicle fusion methods. First, it was shown that assembly of LH2 and LH1-RC in planar lipid bilayers, through vesicle-to-planar membrane formation, could be confirmed by absorption spectroscopy and high resolution atomic force microscopy (AFM). Second, formation of a planar membrane incorporating LH2 molecules made by the vesicle fusion method was corroborated by AFM together with quantitative analysis by surface plasmon resonance (SPR). By combining planar membrane formation and vesicle fusion, in a stepwise manner, LH2 and LH1-RC were successfully organized in the domain-structured planar lipid membrane. This methodology for construction of LH2/LH1-RC assemblies will be a useful experimental platform with which to investigate energy transfer from LH2 to LH1-RC where the relative arrangement of these two complexes can be controlled.

Fluorescent Quantum Dots as Artificial Antennas for Enhanced Light Harvesting and Energy Transfer to Photosynthetic Reaction Centers

The development of artificial photosynthetic systems that utilize solar energy is one of the most challenging goals of chemistry and material sciences. The straightforward way to construct an artificial photosynthetic device for practical solar fuel production for the practical use of solar energy is to mimic the structural and functional organization of the natural photosynthetic machinery. In photosynthetic organisms, light is initially absorbed by antenna protein–pigment complexes in which it induces an excited electronic state (exciton), and then excitons (or electron–hole pairs) are transferred by means of F rster resonance energy transfer (FRET) to specialist chlorophyll cofactors in specialized reaction centers (RCs); here, excitons dissociate into their constituent carriers which are used in chemical transformations for the synthesis of high-energy molecules that fuel the organism. An artificial device that mimics this process for solar energy conversion should include, among other components, an efficient light-harvesting antenna capable of transferring the excitation energy to the RC. Based on the principle of photosynthesis, a variety of artificial antenna systems have been developed using supramolecular chemistry in which dendrimers incorporate porphyrins or other organic fluorophores or organometallic complexes. Although efficient excitation-energy transfer was obtained in such systems, the use of organic fluorophores in light-harvesting systems is rather limited because of their narrow spectral windows for light-collecting and lack of photostability. Recently it was suggested that inorganic nanocrystals, which are able to collect light over a wide spectral window, may achieve significantly greater absorption than natural photosystems, thus enhancing and could thus be used to enhance the light-harvesting process. Simultaneously, these nanocrystals may also be very efficient in excitationenergy transfer. This has led us to contemplate the development of hybrid materials in which light energy harvested by the nanocrystals in the optical region may be transferred to the RC in order to enhance the efficiency of the photosynthetic process. The simplest and best understood photosynthetic RC is that found in purple bacteria (Rhodobacter sphaeroides, for example). Although RCs from different photosynthetic organisms vary in their structure and composition, they are always composed of complexes of pigments and proteins, and RC fromRb. sphaeroides is known to be a good model of all the photosynthetic RCs. Here, we demonstrate that photoluminescent quantum dots (QDs) of these selected photoluminescence (PL) wavelengths may be tagged with the RC of Rh. sphaeroides in such a way that FRET from the QD to the RC is realized (Figure 1). A nearly threefold increase in the rate of generation of excitons in the RC is demonstrated, and theoretical estimates predict even stronger enhancements, thus indicating that further optimization is possible. Advances in inorganic synthesis have resulted in the production of monodispersed QDs such as highly photoluminescent CdSe/ZnS core/shell and CdTe nanocrystals. The light absorption by these QDs appears as a quasicontinuous superposition of peaks with extinction coefficients orders of magnitude higher than those of organic molecules. QDs are ultrastable against photobleaching, and the quantum [*] Prof. I. Nabiev CIC NanoGUNE Consolider, 20018 San Sebastian (Spain) and EA n83798, Universit de Reims Champagne-Ardenne 51100 Reims (France) and Ikerbasque, Basque Foundation for Science 48011 Bilbao (Spain) Fax: (+34)943-574-001 E-mail: i.nabiev@nanogune.eu

Artificial Photosynthesis

One-dimensional channel materials, such as zeolites and mesoporous silicas, are very attractive hosts for the preparation and investigation of hierarchically organized structures, presenting a successive ordering from the molecular up to macroscopic scale. The focus of this article is on artificial photonic antenna systems and on photocatalytically active layers that have been built by incorporating organic dyes, complexes, metal cations and clusters into 1-D nanochannel materials. We show that zeolite L as a host material allows for the design and preparation of a large variety of highly organized host–guest systems. The combination of a tuneable host morphology and the possibility of obtaining highly organized molecular patterns of guests leads to a variety of potential optical and photoelectronic applications. Strongly absorbing systems exhibiting efficient FRET along the c-axis of the zeolite crystals are accessible by sequential inclusion of multiple types of dyes. These new light-harvesting materials offer unique possibilities as building blocks for solar-energy conversion devices. A complementary approach consists in integrating photochemically active substances into zeolite monolayers coated on an electrode and taking advantage of intrazeolite processes for designing a reversible electrode for photocatalytic water oxidation. The photoelectrochemical water splitting capability of systems based on Ag+/AgCl/Agn-zeolite photoanodes are discussed.