scholarly journals Femtosecond visible transient absorption spectroscopy of chlorophyll-f-containing photosystem II

2020 ◽  
Vol 117 (37) ◽  
pp. 23158-23164
Author(s):  
Noura Zamzam ◽  
Rafal Rakowski ◽  
Marius Kaucikas ◽  
Gabriel Dorlhiac ◽  
Sefania Viola ◽  
...  
Keyword(s):  
Energy Transfer ◽  
Excited State ◽  
Photosystem Ii ◽  
Charge Separation ◽  
Transient Absorption ◽  
Spectral Feature ◽  
Cation Radical ◽  
Stimulated Emission ◽  
Transient Absorption Spectroscopy ◽  
Long Wavelength

The recently discovered, chlorophyll-f-containing, far-red photosystem II (FR-PSII) supports far-red light photosynthesis. Participation and kinetics of spectrally shifted far-red pigments are directly observable and separated from that of bulk chlorophyll-a. We present an ultrafast transient absorption study of FR-PSII, investigating energy transfer and charge separation processes. Results show a rapid subpicosecond energy transfer from chlorophyll-a to the long-wavelength chlorophylls-f/d. The data demonstrate the decay of an ∼720-nm negative feature on the picosecond-to-nanosecond timescales, coinciding with charge separation, secondary electron transfer, and stimulated emission decay. An ∼675-nm bleach attributed to the loss of chl-a absorption due to the formation of a cation radical, PD1+•, is only fully developed in the nanosecond spectra, indicating an unusually delayed formation. A major spectral feature on the nanosecond timescale at 725 nm is attributed to an electrochromic blue shift of a FR-chlorophyll among the reaction center pigments. These time-resolved observations provide direct experimental support for the model of Nürnberg et al. [D. J. Nürnberg et al., Science 360, 1210–1213 (2018)], in which the primary electron donor is a FR-chlorophyll and the secondary donor is chlorophyll-a (PD1 of the central chlorophyll pair). Efficient charge separation also occurs using selective excitation of long-wavelength chlorophylls-f/d, and the localization of the excited state on P720* points to a smaller (entropic) energy loss compared to conventional PSII, where the excited state is shared over all of the chlorin pigments. This has important repercussions on understanding the overall energetics of excitation energy transfer and charge separation reactions in FR-PSII.

Donor-acceptor conjugates derived from cobalt porphyrin and fullerene via metal-ligand axial coordination: Formation and excited state charge separation

2021 ◽  
pp. A-N
Author(s):  
Dili R. Subedi ◽  
Youngwoo Jang ◽  
Ashwin Ganesan ◽  
Sydney Schoellhorn ◽  
Ryan Reid ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Excited State ◽  
Charge Separation ◽  
Transient Absorption ◽  
Transient Absorption Spectroscopy ◽  
Cobalt Porphyrin ◽  
Axial Coordination ◽  
Cobalt Porphyrins ◽  
Donor Acceptor ◽  
Metal Ligand

Two types of cobalt porphyrins, viz., meso-tetrakis(tolylporphyrinato)cobalt(II), (TTP)Co (1), and meso-tetrakis(triphenylamino porphyrinato)cobalt(II), [(TPA)4P]Co, (2) were self-assembled via metal-ligand axial coordination of phenyl imidazole functionalized fulleropyrrolidine, ImC[Formula: see text] to form a new series of donor–acceptor constructs. A 1:2 complex formation with ImC[Formula: see text] was established in the case of (TTP)Co while for [(TPA)4P]Co only a 1:1 complex was possible to positively identify. The binding constants [Formula: see text] and [Formula: see text] for step-wise addition of ImC[Formula: see text] to (TTP)Co were found to be 1.07 × 105 and 3.20 × 104 M[Formula: see text], respectively. For [(TPA)4P]Co:ImC[Formula: see text], the measured [Formula: see text] values was found to be 6.48 × 104 M[Formula: see text], slightly smaller than that observed for (TTP)Co. Although both cobalt porphyrins were non-fluorescent, they were able to quench the fluorescence of ImC[Formula: see text] indicating occurrence of excited state events in the supramolecular donor-acceptor complexes. Electrochemistry coupled with spectroelectrochemistry, revealed the formation of cobalt(III) porphyrin cation instead of a cobalt(II) porphyrin radical cation, as the main product, during oxidation of phenyl imidazole coordinated cobalt porphyrin. With the help of computational and electrochemical results, an energy level diagram was constructed to witness excited state photo-events. Competitive energy and electron transfer from excited CoP to coordinated ImC[Formula: see text], and electron transfer from Im1C[Formula: see text]* to cobalt(II) porphyrin resulting into the formation of PCo[Formula: see text]:ImC[Formula: see text] charge separated state was possible to envision from the energy diagram. Finally, using femtosecond transient absorption spectroscopy and data analysis by Glotaran, it was possible to establish sequential occurrence of energy transfer and charge separation processes. The lifetime of the final charge separated state was [Formula: see text] 2 ns. A slightly better charge stabilization was observed in the case of [(TPA)4P]Co:ImC[Formula: see text] due to the presence of electron rich, peripheral triphenylamine substituents on the cobalt porphyrin.

Unveiling excited state energy transfer and charge transfer in a host/guest coordination cage

2018 ◽  
Vol 20 (4) ◽  
pp. 2205-2210 ◽  
Author(s):  
Rui-Ling Zhang ◽  
Yang Yang ◽  
Song-Qiu Yang ◽  
Ke-Li Han
Keyword(s):  
Energy Transfer ◽  
Excited State ◽  
State Energy ◽  
Transient Absorption ◽  
Transient Absorption Spectroscopy ◽  
Dynamic Processes ◽  
Excited State Energy ◽  
Femtosecond Transient Absorption ◽  
Femtosecond Transient Absorption Spectroscopy ◽  
Excited State Dynamic

Ultrafast excited-state dynamic processes, charge and energy transfer in a HGCT system are unveiled by using femtosecond transient absorption spectroscopy.

scholarly journals Photoactive Anthraquinone-Based Host-Guest Assembly for Long-Lived Charge Separation

2020 ◽  
Author(s):  
Ajay Jha ◽  
Kaustubh R. Mote ◽  
Suman Chandra ◽  
Perunthiruthy K. Madhu ◽  
Jyotishman Dasgupta
Keyword(s):  
Charge Transport ◽  
Charge Separation ◽  
Transient Absorption ◽  
Cation Radical ◽  
Transient Absorption Spectroscopy ◽  
Paramagnetic Resonance ◽  
Transport Pathways ◽  
Charge Localization ◽  
Efficient Charge ◽  
Transport Channels

<p>Porous 2D-covalent organic frameworks (COF) that are assembled axially through weak π-stacking interactions can provide reticular charge transport channels while playing host to kinetically stabilized reactive molecular redox-states. Here we demonstrate the above paradigm by constructing a host-guest supramolecular charge transfer (CT) assembly using photoactive anthraquinone-based crystalline COF as an acceptor while incarcerating electron donor N,N-dimethylaniline (DMA) inside it. Employing femtosecond broadband transient absorption spectroscopy in combination with electron paramagnetic resonance (EPR) studies, we show that the CT occurs rapidly within <110 femtoseconds after photoexcitation, subsequently leading to long-lived charge separation with 13% quantum efficiency at room temperature. Photoinduced EPR signature of the long-lived confined DMA cation radical confirms the disparate regions of charge localization while <sup>1</sup>H-<sup>13</sup>C correlation experiments using solid-state NMR spectroscopy enumerate the packing of the amines inside the host-guest COF assembly. Our work demonstrates the potency of rationally designed charge transport pathways in supramolecular assemblies for efficient charge separation which if optimally tuned should pave the way for COF-based photocatalytic reaction centres. </p>

scholarly journals Bifurcation of excited state trajectories toward energy transfer or electron transfer directed by wave function symmetry

2021 ◽  
Vol 118 (4) ◽  
pp. e2018521118
Author(s):  
Paola S. Oviedo ◽  
Luis M. Baraldo ◽  
Alejandro Cadranel
Keyword(s):  
Electron Transfer ◽  
Wave Function ◽  
Energy Transfer ◽  
Excited State ◽  
Excited States ◽  
Transient Absorption ◽  
Transient Absorption Spectroscopy ◽  
Differential Behavior ◽  
Donor Acceptor ◽  
Kinetic Barriers

This work explores the concept that differential wave function overlap between excited states can be engineered within a molecular chromophore. The aim is to control excited state wave function symmetries, so that symmetry matches or mismatches result in differential orbital overlap and define low-energy trajectories or kinetic barriers within the excited state surface, that drive excited state population toward different reaction pathways. Two donor–acceptor assemblies were explored, where visible light absorption prepares excited states of different wave function symmetry. These states could be resolved using transient absorption spectroscopy, thanks to wave function symmetry-specific photoinduced optical transitions. One of these excited states undergoes energy transfer to the acceptor, while another undertakes a back-electron transfer to restate the ground state. This differential behavior is possible thanks to the presence of kinetic barriers that prevent excited state equilibration. This strategy can be exploited to avoid energy dissipation in energy conversion or photoredox catalytic schemes.

scholarly journals Photoactive Anthraquinone-Based Host-Guest Assembly for Long-Lived Charge Separation

2020 ◽  
Author(s):  
Ajay Jha ◽  
Kaustubh R. Mote ◽  
Suman Chandra ◽  
Perunthiruthy K. Madhu ◽  
Jyotishman Dasgupta
Keyword(s):  
Charge Transport ◽  
Charge Separation ◽  
Transient Absorption ◽  
Cation Radical ◽  
Transient Absorption Spectroscopy ◽  
Paramagnetic Resonance ◽  
Transport Pathways ◽  
Charge Localization ◽  
Efficient Charge ◽  
Transport Channels

<p>Porous 2D-covalent organic frameworks (COF) that are assembled axially through weak π-stacking interactions can provide reticular charge transport channels while playing host to kinetically stabilized reactive molecular redox-states. Here we demonstrate the above paradigm by constructing a host-guest supramolecular charge transfer (CT) assembly using photoactive anthraquinone-based crystalline COF as an acceptor while incarcerating electron donor N,N-dimethylaniline (DMA) inside it. Employing femtosecond broadband transient absorption spectroscopy in combination with electron paramagnetic resonance (EPR) studies, we show that the CT occurs rapidly within <110 femtoseconds after photoexcitation, subsequently leading to long-lived charge separation with 13% quantum efficiency at room temperature. Photoinduced EPR signature of the long-lived confined DMA cation radical confirms the disparate regions of charge localization while <sup>1</sup>H-<sup>13</sup>C correlation experiments using solid-state NMR spectroscopy enumerate the packing of the amines inside the host-guest COF assembly. Our work demonstrates the potency of rationally designed charge transport pathways in supramolecular assemblies for efficient charge separation which if optimally tuned should pave the way for COF-based photocatalytic reaction centres. </p>

Thymine Dimerization Induced by Oxidative DNA Lesions and Epigenetic Intermediates via Triplet-Triplet Energy Transfer

2020 ◽  
Author(s):  
Mauricio Lineros-Rosa ◽  
Antonio Francés-Monerris ◽  
Antonio Monari ◽  
Miguel Angél Miranda ◽  
Virginie Lhiaubet-Vallet
Keyword(s):  
Energy Transfer ◽  
Excitation Energy ◽  
Transient Absorption ◽  
Theoretical Calculations ◽  
Dna Lesions ◽  
Transient Absorption Spectroscopy ◽  
Triplet Energy ◽  
Pyrimidine Dimers ◽  
Triplet Energy Transfer ◽  
Dna Nucleobases

Interaction of nucleic acids with light is a scientific question of paramount relevance not only in the understanding of life functioning and evolution, but also in the insurgence of diseases such as malignant skin cancer and in the development of biomarkers and novel light-assisted therapeutic tools. This work shows that the UVA portion of sunlight, not absorbed by canonical DNA nucleobases, can be absorbed by 5-formyluracil (ForU) and 5-formylcytosine (ForC), two ubiquitous oxidative lesions and epigenetic intermediates present in living beings in natural conditions. We measure the strong propensity of these molecules to populate triplet excited states able to transfer the excitation energy to thymine-thymine dyads, inducing the formation of the highly toxic and mutagenic cyclobutane pyrimidine dimers (CPDs). By using steady-state and transient absorption spectroscopy, NMR, HPLC, and theoretical calculations, we quantify the differences in the triplet-triplet energy transfer mediated by ForU and ForC, revealing that the former is much more efficient in delivering the excitation energy and producing the CPD photoproduct. Although significantly slower than ForU, ForC is also able to harm DNA nucleobases and therefore this process has to be taken into account as a viable photosensitization mechanism. The present findings evidence a rich photochemistry crucial to understand DNA photodamage and of potential use in the development of biomarkers and non-conventional photodynamic therapy agents.

Sign in / Sign up

Export Citation Format

Share Document