Elucidating light-induced changes in excitation energy transfer of photosystem I and II in whole cells of two model cyanobacteria.

Excitation energy transfer between the photochemically active protein complexes is key for photosynthetic processes. Phototrophic organisms like cyanobacteria experience subtle changes in irradiance under natural conditions. Such changes need adjustments to the excitation energy transfer between the photosystems for sustainable growth.

Architecture and functional regulation of a plant PSII-LHCII megacomplex.

Photosystem II (PSII) splits water in oxygenic photosynthesis on Earth. The structure and function of the CSM-type PSII-LHCII (light-harvesting complex II) megacomplexes from the wild-type and PsbR-deletion mutant plants are studied through electron microscopy (EM), structural mass spectrometry, and ultrafast fluorescence spectroscopy [time-resolved fluorescence (TRF)]. The cryo-EM structure of a type I CSM megacomplex demonstrates that the three domains of PsbR bind to the stromal side of D1, D2, and CP43; associate with the single transmembrane helix of the redox active Cyt ; and stabilize the luminal extrinsic PsbP, respectively.

Structural and spectroscopic characterization of the peridinin-chlorophyll a-protein (PCP) complex from Heterocapsa pygmaea (HPPCP).

Light harvesting proteins are optimized to efficiently collect and transfer light energy for photosynthesis. In eukaryotic dinoflagellates these complexes utilize chlorophylls and a special carotenoid, peridinin, and arrange them for efficient excitation energy transfer. At the same time, the carotenoids protect the system by quenching harmful chlorophyll triplet states.

Photonic Properties of Thin Films Composed of Gallium Nitride Quantum Dots Synthesized by Nonequilibrium Plasma Aerotaxy.

Gallium nitride quantum dots (GaN QDs) are a promising material for optoelectronics, but the synthesis of freestanding GaN QDs remains a challenge. To date, the size-dependent photonic properties of freestanding GaN QDs have not been reported. Here, we examine the photonic properties exhibited by thin films composed of GaN QDs synthesized by nonequilibrium plasma aerotaxy.

Energy dissipation efficiency in the CP43 assembly intermediate complex of photosystem II.

Photosystem II in oxygenic organisms is a large membrane bound rapidly turning over pigment protein complex. During its biogenesis, multiple assembly intermediates are formed, including the CP43-preassembly complex (pCP43). To understand the energy transfer dynamics in pCP43, we first engineered a His-tagged version of the CP43 in a CP47-less strain of the cyanobacterium Synechocystis 6803.

Transient "-Peak" Is Present in Excited-State Absorption of Central- Isomers of Carotenoids.

Application of femtosecond time-resolved transient absorption spectroscopy on all- and central- isomers of two exemplary carotenoids, lutein and spirilloxanthin, performed at room and cryogenic temperatures in the spectral range expanded toward UV revealed new spectroscopic transient features for the isomers. Notably, particularly for the central- spirilloxanthin, a very distinct additional transient absorption band is observed on the short wavelength side of the main excited-state absorption band of the S state, having the same temporal characteristics as the latter one. This band is absent in transient absorption spectra of all- isomers, suggesting it could be assigned to "transient -peak.

Mass spectrometry and spectroscopic characterization of a tetrameric photosystem I supercomplex from Leptolyngbya ohadii, a desiccation-tolerant cyanobacterium.

Cyanobacteria inhabiting desert biological soil crusts face the harsh conditions of the desert. They evolved a suite of strategies toward desiccation-hydration cycles mixed with high light irradiations, etc. In this study we purified and characterized the structure and function of Photosystem I (PSI) from Leptolyngbya ohadii, a desiccation-tolerant desert cyanobacterium.

Balancing Panchromatic Absorption and Multistep Charge Separation in a Compact Molecular Architecture.

A panchromatic triad and a charge-separation unit are joined in a crossbar architecture to capture solar energy. The panchromatic-absorber triad (T) is comprised of a central free-base porphyrin that is strongly coupled direct ethyne linkages to two perylene-monoimide (PMI) groups. The charge-separation unit incorporates a free-base or zinc chlorin (C or ZnC) as a hole acceptor (or electron donor) and a perylene-diimide (PDI) as an electron acceptor, both attached to the porphyrin diphenylethyne linkers.

Biochemical and spectroscopic characterizations of the oligomeric antenna of the coral symbiotic Symbiodiniaceae Fugacium kawagutii.

Light-harvesting antennas in photosynthesis capture light energy and transfer it to the reaction centers (RCs) where photochemistry takes place. The sustainable growth of the reef-building corals relies on a constant supply of the photosynthates produced by the endosymbiotic dinoflagellate, belonging to the family of Symbiodiniaceae. The antenna system in this group consists of the water-soluble peridinin-chlorophyll a-protein (PCP) and the intrinsic membrane chlorophyll a-chlorophyll c-peridinin protein complex (acpPC).

Evaluation of the Photophysical Properties of Two Scintillators: Crystalline -terphenyl and Plastic-Embedded 2,5-Diphenyloxazole Dye (EJ-276) at Room and Cryogenic Temperatures.

The photophysical characterization of two dyes used as scintillators, crystalline -terphenyl and EJ-276, a plastic heavily doped with 2,5-diphenyloxazole (DPO), was investigated with steady-state absorption, time-resolved emission, and transient absorption at room and cryogenic temperatures. Application of time-gated emission spectroscopy allowed for the measurement of phosphorescence spectra and their temporal dynamics. The photophysical properties of plastic-embedded DPO are not substantially altered compared to those previously determined for this dye in solvents.

Photophysical Properties and Electronic Structure of Hydroporphyrin Dyads Exhibiting Strong Through-Space and Through-Bond Electronic Interactions.

Electronic interactions between tetrapyrroles are utilized in natural photosynthetic systems to tune the light-harvesting and energy-/charge-transfer processes in these assemblies. Such interactions also can be employed to tailor the electronic properties of tetrapyrrolic dyads and larger arrays for use in materials science and biomedical research. Here, we have utilized static and time-resolved optical spectroscopy to characterize the optical absorption and emission properties of a set of chlorin and bacteriochlorin dyads with varying degrees of through-bond (TB) and through-space (TS) interactions between the constituent macrocycles.

Introduction of cysteine-mediated quenching in the CP43 protein of photosystem II builds resilience to high-light stress in a cyanobacterium.

Photosystem (PS) II is prone to photodamage both as a direct consequence of light, and indirectly by producing reactive oxygen species. Engineering high-light tolerance in cyanobacteria with minimal impact on PSII function is desirable in synthetic biology. IsiA, a CP43 homolog found exclusively in cyanobacteria, can dissipate excess light energy.

Ability of the Putative Decomposition Products of 2,3-dioxetanes of Indoles to Photosensitize Cyclobutane Pyrimidine Dimer (CPD) Formation and its Implications for the "Dark" (Chemisensitized) Pathway to CPDs in Melanocytes.

The formation of cyclobutane pyrimidine dimers (CPDs) by a "dark" pathway in melanocytes has been attributed to chemisensitization by dioxetanes produced from peroxynitrite oxidation of melanin or melanin precursors. These dioxetanes are proposed to decompose to triplet state compounds which sensitize CPD formation by triplet-triplet energy transfer. To determine whether such compounds are capable of sensitizing CPD formation, the putative decomposition products of 2,3-dioxetanes of variously substituted indoles were synthesized and their triplet state energies determined at 77 K.

Electronic Structure and Excited-State Dynamics of Rylene-Tetrapyrrole Panchromatic Absorbers.

Panchromatic absorbers have potential applications in molecular-based energy-conversion schemes. A prior porphyrin-perylene dyad (, where "MI" denotes monoimide) coupled via an ethyne linker exhibits panchromatic absorption (350-700 nm) and a tetrapyrrole-like lowest singlet excited state with a relatively long singlet excited-state lifetime (τ) and increased fluorescence quantum yield (Φ) versus the parent porphyrin. To explore the extension of panchromaticity to longer wavelengths, three arrays have been synthesized: a chlorin-terrylene dyad (), a bacteriochlorin-terrylene dyad (), and a perylene-porphyrin-terrylene triad (), where the terrylene, a π-extended homologue of perylene, is attached via an ethyne linker.

Spectroscopic investigations of electron and hole dynamics in MAPbBr perovskite film and carrier extraction to PEDOT hole transport layer.

Organometallic halide perovskite (MAPPbBr3), Rust-based Vapor Phase Polymerization (RVPP)-PEDOT hole transporting layers and (RVPP-PEDOT)/MAPPbBr3 dual-layer, deposited on fluorine doped tin oxide glass were studied at room temperature using steady-state absorption, time-resolved photoluminescence imaging and femtosecond time-resolved absorption spectroscopy. Application of these techniques in conjunction with diverse excitation intensities allowed determination of various optoelectronic properties of the perovskite film and the time constant of the hole extraction process. Spectral reconstruction of the bandedge absorption spectrum using Elliot's formula enabled separation of the exciton band.

Photophysical properties of N719 and Z907 dyes, benchmark sensitizers for dye-sensitized solar cells, at room and low temperature.

Two benchmark sensitizers used for dye-sensitized solar cells, ruthenium polypyridyl N719 and Z907 dyes were investigated with spectroscopic methods as steady-state absorption, time-gated phosphorescence and femto-/nanosecond time-resolved transient absorption at room temperature and at 160 K. Aim of this study was to perform comprehensive photophysical study of dye excited singlet and triplet metal-to-ligand charge transfer (MLCT) states including states lifetimes, dependency on temperature and dye concentration and obtain detailed information on the excitation decay pathway. Transient absorption and phosphorescence decay data provided a clearer picture of the dynamics of the excited MLCT states.

A Novel Mode of Photoprotection Mediated by a Cysteine Residue in the Chlorophyll Protein IsiA.

Oxygenic photosynthetic organisms have evolved a multitude of mechanisms for protection against high-light stress. IsiA, a chlorophyll -binding cyanobacterial protein, serves as an accessory antenna complex for photosystem I. Intriguingly, IsiA can also function as an independent pigment protein complex in the thylakoid membrane and facilitate the dissipation of excess energy, providing photoprotection.

Excited-State Properties of Metal-Free (()-2-Cyano-3-(4-(()-2-(6-(4-methoxyphenyl)-9-octyl-9-carbazol-3-yl)vinyl)phenyl)acrylic Acid and ()-2-Cyano-3-(4-(()-4-(diphenylamino)styryl)phenyl)acrylic Acid) and Ru-Based (N719 and Z907) Dyes and Photoinduced Charge Transfer Processes in FTO/TiCl/TiO/Dye Photoanodes Fabricated by Conventional Staining and Potential-Assisted Adsorption.

Excited-state properties of two novel metal-free custom-made dyes [()-2-cyano-3-(4-(()-2-(6-(4-methoxyphenyl)-9-octyl-9-carbazol-3-yl)vinyl)phenyl)acrylic acid] and [()-2-cyano-3-(4-(()-4-(diphenylamino)styryl)phenyl)acrylic acid] and two commercially available Ruthenium-based and dyes were investigated with application of time-resolved absorption and emission. Singlet excited state lifetimes of and were determined in acetonitrile and are 1.4 and 2.

A photosynthetic antenna complex foregoes unity carotenoid-to-bacteriochlorophyll energy transfer efficiency to ensure photoprotection.

Carotenoids play a number of important roles in photosynthesis, primarily providing light-harvesting and photoprotective energy dissipation functions within pigment-protein complexes. The carbon-carbon double bond (C=C) conjugation length of carotenoids (), generally between 9 and 15, determines the carotenoid-to-(bacterio)chlorophyll [(B)Chl] energy transfer efficiency. Here we purified and spectroscopically characterized light-harvesting complex 2 (LH2) from containing the = 7 carotenoid zeta (ζ)-carotene, not previously incorporated within a natural antenna complex.