Panoramic insights into semi-artificial photosynthesis: origin, development, and future perspective

Semi-artificial photosynthetic system (SAPS) integrates the strengths of natural and artificial photosynthesis for solar energy conversion. Synthetic materials and biological components both play indispensable roles, where the former can be...

Artificial quantum photosynthetic materials

Photosynthesis has been shown to be a highly efficient process for energy transfer in plants and bacteria. It has been proposed that quantum mechanics plays a key role in this energy transfer process. There has been evidence that photosynthetic systems may exhibit quantum coherence. As artificial light-harvesting complexes have been proposed to mimic photosynthesis, it is prudent that artificial photosynthetic materials should also be tested for quantum coherence. To date, such studies have not been reported. In this work, we examine one such system, the BODIPY light harvesting complex (LHC), which has been shown to exhibit classical energy transfer via Förster resonance energy transfer. We compare the photon absorption of the LHC with the BODIPY chromophore by performing UV-visible, transient absorption, broadband pump-probe (BBPP) and two-dimensional electronic (2DES) spectroscopy. The 2DES and BBPP show evidence for quantum coherence, with oscillation frequencies of 100 cm-1 and 600 cm-1, which are attributable to vibronic, or exciton-phonon type coupling. Further computational analysis suggests strong couplings of the molecular orbitals of the LHC resulting from the stacking of neighbouring BODIPY chromophore units may contribute to undesirable hypochromic effects .

Tubular J-aggregates of cyanine dyes in the near-infrared

Developing improved organic infrared emitters has wide-ranging applicability in fields such as bioimaging or energy harvesting. We synthesize redshifted analogues of C8S3, a well-known cyanine dye that self assembles into tubular aggregates which have attracted widespread attention as artificial photosynthetic complexes. Despite the elongated dye structure, the new pentamethine dyes retain their tubular self-assembly and emit at near-infrared wavelengths. Cryo-electron microscopy and detailed photophysical characterization of the new aggregates reveal similar absorption lineshapes with ~100 nm of redshift, as well as supramolecular morphologies that resemble their trimethine counterparts; the pentamethine aggregates generally show more disorder and decreased superradiance, suggesting that more ordered structures yield more robust photophysical properties. These results provide design principles of superradiant organic emitters, expand the chemical space of near-infrared aggregates, and introduce two additional wavelength-specific antennae as model systems for study.

A Brief History of Photoactive Interlocked Systems Assembled by Transition Metal Template Synthesis

More than three decades of research efforts have yielded powerful methodologies based on transition metal template-directed syntheses for the assembly of a huge number of interlocked systems, molecular knots, machines and synthesizers. Such template techniques have been applied in the preparation of mechanically linked electron donor–acceptor artificial photosynthetic models. Consequently, synthetic challenging photoactive rotaxanes and catenanes have been reported, in which the chromophores are not covalently linked but are still associated with undergoing sequential energy (EnT) and electron transfer (ET) processes upon photoexcitation. Many interlocked photosynthetic models produce highly energetic, but still long-living charge separated states (CSS). The present work describes in a historical perspective some key advances in the field of photoactive interlocked systems assembled by transition metal template techniques, which illustrate the usefulness of rotaxanes and catenanes as molecular scaffolds to organize electron donor–acceptor groups. The effects of molecular dynamics, molecular topology, as well as the role of the transition metal ion used as template species, on the thermodynamic and kinetic parameters of the photoinduced energy and electron transfer processes in the interlocked systems are also discussed.

Tubular J-aggregates of cyanine dyes in the near-infrared

Developing improved organic infrared emitters has wide-ranging applicability in fields such as bioimaging or energy harvesting. We synthesize redshifted analogues of C8S3, a well-known cyanine dye that self assembles into tubular aggregates which have attracted widespread attention as artificial photosynthetic complexes. Despite the elongated dye structure, the new pentamethine dyes retain their tubular self-assembly and emit at near-infrared wavelengths. Cryo-electron microscopy and detailed photophysical characterization of the new aggregates reveal similar absorption lineshapes with ~100 nm of redshift, as well as supramolecular morphologies that resemble their trimethine counterparts; the pentamethine aggregates generally show more disorder and decreased superradiance, suggesting that more ordered structures yield more robust photophysical properties. These results provide design principles of superradiant organic emitters, expand the chemical space of near-infrared aggregates, and introduce two additional wavelength-specific antennae as model systems for study.

Characterizing the supercomplex association of photosynthetic complexes in cyanobacteria

The light reactions of photosynthesis occur in thylakoid membranes that are densely packed with a series of photosynthetic complexes. The lateral organization and close association of photosynthetic complexes in native thylakoid membranes are vital for efficient light harvesting and energy transduction. Recently, analysis of the interconnections between photosynthetic complexes to form supercomplexes has garnered great interest. In this work, we report a method integrating immunoprecipitation, mass spectrometry and atomic force microscopy to identify the inter-complex associations of photosynthetic complexes in thylakoid membranes from the cyanobacterium Synechococcus elongatus PCC 7942. We characterize the preferable associations between individual photosynthetic complexes and binding proteins involved in the complex–complex interfaces, permitting us to propose the structural models of photosynthetic complex associations that promote the formation of photosynthetic supercomplexes. We also identified other potential binding proteins with the photosynthetic complexes, suggesting the highly connecting networks associated with thylakoid membranes. This study provides mechanistic insight into the physical interconnections of photosynthetic complexes and potential partners, which are crucial for efficient energy transfer and physiological acclimatization of the photosynthetic apparatus. Advanced knowledge of the protein organization and interplay of the photosynthetic machinery will inform rational design and engineering of artificial photosynthetic systems to supercharge energy production.

Solar Energy and its Multiple Applications

Solar energy is commercially exploited to provide benefits in the form of various products and capabilities applying a range of technologies. Electricity generation is achieved either directly from photovoltaic cells made of various materials or indirectly through the steam production from concentrating solar thermal systems. Whereas solar thermal power generation requires large scale plants, photovoltaic systems can be large or small in scale and building integrated, if required. Both types of generation can be standalone or connected to power grids. Solar energy is also extensively used for water and space heating, cooling and drying purposes. It can also be stored and/or transformed into a range of clean fuels and contributes energy to the manufacture of various energy-intensive products. The research into the artificial photosynthetic synthesis of biofuels although encouraging is, however, yet to be achieved commercially exploited on a large scale. Much scope remains for innovative technology breakthroughs to further improve the efficiency and uptake of all the solar energy technologies currently exploited or under investigation. Policy frameworks, renewable portfolio standards, feed-in tariffs and net-metering play an important and ongoing role in promoting the uptake of photovoltaics in particular.