scholarly journals Geometries and Terahertz Motions Driving Quintet Multiexcitons and Ultimate Triplet-Triplet Dissociations via the Intramolecular Singlet-Fissions

2020 ◽  
Author(s):  
Yasuhiro Kobori ◽  
Masaaki Fuki ◽  
Shunta Nakamura ◽  
Taku Hasobe
Keyword(s):  
Molecular Mechanisms ◽  
Molecular Conformation ◽  
High Energy ◽  
Strongly Correlated ◽  
Spin Conversion ◽  
Paramagnetic Resonance ◽  
Time Resolved ◽  
Strongly Coupled ◽  
Singlet Exciton ◽  
Spin Distributions

Importance of vibronic effects has been highlighted for the singlet-fission (SF) that convert one high-energy singlet exciton into doubled triplet excitons, as strongly correlated multiexcitons. However, molecular mechanisms of spin conversion processes and ultimate de-couplings in the multiexcitons are poorly understood. We have analyzed geometries and exchange couplings of the photoinduced multiexcitons in the pentacene dimers bridged by a phenylene at ortho and meta positions [denoted as <i>o</i>-(Pc)<sub>2</sub> and <i>m</i>-(Pc)<sub>2</sub>] by simulations of the time-resolved electron paramagnetic resonance spectra. We clarified that terahertz molecular conformation dynamics plays a role on the spin conversion from the singlet strongly coupled multiexcitons <sup>1</sup>(TT) to the quintet state <sup>5</sup>(TT). The strongly coupled <sup>5</sup>(TT) multiexcitons are revealed to possess entirely planar conformations stabilized by mutually delocalized spin distributions, while the intramolecular de-coupled spin-correlated triplet pairs generated at 1 microsecond are also stabilized by distorted conformations resulting in two separately localized biradical characters.

scholarly journals Geometries and Terahertz Motions Driving Quintet Multiexcitons and Ultimate Triplet-Triplet Dissociations via the Intramolecular Singlet-Fissions

2020 ◽  
Author(s):  
Yasuhiro Kobori ◽  
Masaaki Fuki ◽  
Shunta Nakamura ◽  
Taku Hasobe
Keyword(s):  
Molecular Mechanisms ◽  
Molecular Conformation ◽  
High Energy ◽  
Strongly Correlated ◽  
Spin Conversion ◽  
Paramagnetic Resonance ◽  
Time Resolved ◽  
Strongly Coupled ◽  
Singlet Exciton ◽  
Spin Distributions

Importance of vibronic effects has been highlighted for the singlet-fission (SF) that convert one high-energy singlet exciton into doubled triplet excitons, as strongly correlated multiexcitons. However, molecular mechanisms of spin conversion processes and ultimate de-couplings in the multiexcitons are poorly understood. We have analyzed geometries and exchange couplings of the photoinduced multiexcitons in the pentacene dimers bridged by a phenylene at ortho and meta positions [denoted as <i>o</i>-(Pc)<sub>2</sub> and <i>m</i>-(Pc)<sub>2</sub>] by simulations of the time-resolved electron paramagnetic resonance spectra. We clarified that terahertz molecular conformation dynamics plays a role on the spin conversion from the singlet strongly coupled multiexcitons <sup>1</sup>(TT) to the quintet state <sup>5</sup>(TT). The strongly coupled <sup>5</sup>(TT) multiexcitons are revealed to possess entirely planar conformations stabilized by mutually delocalized spin distributions, while the intramolecular de-coupled spin-correlated triplet pairs generated at 1 microsecond are also stabilized by distorted conformations resulting in two separately localized biradical characters.

Long-lived Triplet Excitons Formed by Exergonic Intramolecular Singlet Fission of an Adamantane-linked Tetracene Dyad

2019 ◽  
Author(s):  
Yasunori Matsui ◽  
Shuhei Kawaoka ◽  
Hiroki Nagashima ◽  
Tatsuo Nakagawa ◽  
Naoki Okamura ◽  
...  
Keyword(s):  
Conformational Dynamics ◽  
High Energy ◽  
Fluorescence Decay ◽  
Singlet Fission ◽  
Paramagnetic Resonance ◽  
Time Resolved ◽  
Triplet Pair ◽  
Electron Paramagnetic ◽  
Effective Conservation ◽  
Moderate Interaction

<div>An adamantane-linked tetracene dyad (Tc–Ad–Tc) undergoes exergonic intramolecular singlet fission (SF), producing longlived (τ = 175 μs) and high-energy (2 x 1.03 eV) multiexcitons. Timeresolved absorption, fluorescence decay, and electron paramagnetic resonance (EPR) spectroscopic analysis revealed that the long-lived triplet species is generated in this system via correlated triplet pair having singlet and quintet characteristics. Time-resolved EPR analysis revealed that conversion of <sup>1</sup>(<sup>3</sup>Tc–Ad–<sup>3</sup>Tc)* -> <sup>5</sup>(<sup>3</sup>Tc–Ad–<sup>3</sup>Tc)* requires small conformational dynamics accompanied by molecular motion. Analysis of the geometries of the quintet states shows that formation of the long-lived multiexciton is enabled by precise and close alignment of the tetracene moieties, which leads to their moderate interaction in the singlet excited state, while triplet–triplet annihilation is prevented by quintet generation. The presence of aliphatic linkages, like the rigid adamantane group, might enable effective conservation of intrinsic S<sub>1</sub> and T<sub>1</sub> levels of the original monomers, and moderate bridge-mediated σ–π interaction leading to exergonic intramolecular SF involving <sup>1</sup>Tc*–Ad–Tc -> <sup>1</sup>(<sup>3</sup>Tc–Ad–<sup>3</sup>Tc)*.</div><div><br></div>

Long-lived Triplet Excitons Formed by Exergonic Intramolecular Singlet Fission of an Adamantane-linked Tetracene Dyad

2019 ◽  
Author(s):  
Yasunori Matsui ◽  
Shuhei Kawaoka ◽  
Hiroki Nagashima ◽  
Tatsuo Nakagawa ◽  
Naoki Okamura ◽  
...  
Keyword(s):  
Conformational Dynamics ◽  
High Energy ◽  
Fluorescence Decay ◽  
Singlet Fission ◽  
Paramagnetic Resonance ◽  
Time Resolved ◽  
Triplet Pair ◽  
Electron Paramagnetic ◽  
Effective Conservation ◽  
Moderate Interaction

<div>An adamantane-linked tetracene dyad (Tc–Ad–Tc) undergoes exergonic intramolecular singlet fission (SF), producing longlived (τ = 175 μs) and high-energy (2 x 1.03 eV) multiexcitons. Timeresolved absorption, fluorescence decay, and electron paramagnetic resonance (EPR) spectroscopic analysis revealed that the long-lived triplet species is generated in this system via correlated triplet pair having singlet and quintet characteristics. Time-resolved EPR analysis revealed that conversion of <sup>1</sup>(<sup>3</sup>Tc–Ad–<sup>3</sup>Tc)* -> <sup>5</sup>(<sup>3</sup>Tc–Ad–<sup>3</sup>Tc)* requires small conformational dynamics accompanied by molecular motion. Analysis of the geometries of the quintet states shows that formation of the long-lived multiexciton is enabled by precise and close alignment of the tetracene moieties, which leads to their moderate interaction in the singlet excited state, while triplet–triplet annihilation is prevented by quintet generation. The presence of aliphatic linkages, like the rigid adamantane group, might enable effective conservation of intrinsic S<sub>1</sub> and T<sub>1</sub> levels of the original monomers, and moderate bridge-mediated σ–π interaction leading to exergonic intramolecular SF involving <sup>1</sup>Tc*–Ad–Tc -> <sup>1</sup>(<sup>3</sup>Tc–Ad–<sup>3</sup>Tc)*.</div><div><br></div>

The promises and perfidy of cryomicroscopy and analysis

1994 ◽  
Vol 52 ◽  
pp. 382-383
Author(s):  
Patrick Echlin
Keyword(s):  
Low Temperature ◽  
High Energy ◽  
Short Paper ◽  
List Type ◽  
Time Resolved ◽  
Energy Beam ◽  
Cellular Analysis ◽  
Dissolved Ions ◽  
Embedding Medium ◽  
Low Temperature Microscopy

The unusual title of this short paper and its accompanying tutorial is deliberate, because the intent is to investigate the effectiveness of low temperature microscopy and analysis as one of the more significant elements of the less interventionist procedures we can use to prepare, examine and analyse hydrated and organic materials in high energy beam instruments. The promises offered by all these procedures are well rehearsed and the litany of petitions and responses may be enunciated in the following mantra.Vitrified water can form the perfect embedding medium for bio-organic samples.Frozen samples provide an important, but not exclusive, milieu for the in situ sub-cellular analysis of the dissolved ions and electrolytes whose activities are central to living processes.The rapid conversion of liquids to solids provides a means of arresting dynamic processes and permits resolution of the time resolved interactions between water and suspended and dissolved materials.The low temperature environment necessary for cryomicroscopy and analysis, diminish, but alas do not prevent, the deleterious side effects of ionizing radiation.Sample contamination is virtually eliminated.

scholarly journals Probing the interplay between lattice dynamics and short-range magnetic correlations in CuGeO3 with femtosecond RIXS

2021 ◽  
Vol 6 (1) ◽  
Author(s):  
E. Paris ◽  
C. W. Nicholson ◽  
S. Johnston ◽  
Y. Tseng ◽  
M. Rumo ◽  
...  
Keyword(s):  
Short Range ◽  
Degrees Of Freedom ◽  
Time Resolved ◽  
Model Calculations ◽  
Spin Correlations ◽  
Singlet Exciton ◽  
Magnetic Correlations ◽  
Local Lattice ◽  
Frustrated Systems ◽  
A Charge

AbstractInvestigations of magnetically ordered phases on the femtosecond timescale have provided significant insights into the influence of charge and lattice degrees of freedom on the magnetic sub-system. However, short-range magnetic correlations occurring in the absence of long-range order, for example in spin-frustrated systems, are inaccessible to many ultrafast techniques. Here, we show how time-resolved resonant inelastic X-ray scattering (trRIXS) is capable of probing such short-ranged magnetic dynamics in a charge-transfer insulator through the detection of a Zhang–Rice singlet exciton. Utilizing trRIXS measurements at the O K-edge, and in combination with model calculations, we probe the short-range spin correlations in the frustrated spin chain material CuGeO3 following photo-excitation, revealing a strong coupling between the local lattice and spin sub-systems.

scholarly journals High-Quality Green-Emitting Nanodiamonds Fabricated by HPHT Sintering of Polycrystalline Shockwave Diamonds

2020 ◽  
Vol 15 (1) ◽  
Author(s):  
Vladimir Yu. Osipov ◽  
Fedor M. Shakhov ◽  
Kirill V. Bogdanov ◽  
Kazuyuki Takai ◽  
Takuya Hayashi ◽  
...  
Keyword(s):  
Polycrystalline Diamond ◽  
Particle Beam ◽  
Production Method ◽  
High Energy ◽  
Nitrogen Vacancy ◽  
High Energy Particle ◽  
Paramagnetic Resonance ◽  
Precursor Material ◽  
Mean Size ◽  
Characteristic Features

Abstract We demonstrate a high-pressure, high-temperature sintering technique to form nitrogen-vacancy-nitrogen centres in nanodiamonds. Polycrystalline diamond nanoparticle precursors, with mean size of 25 nm, are produced by the shock wave from an explosion. These nanoparticles are sintered in the presence of ethanol, at a pressure of 7 GPa and temperature of 1300 °C, to produce substantially larger (3–4 times) diamond crystallites. The recorded spectral properties demonstrate the improved crystalline quality. The types of defects present are also observed to change; the characteristic spectral features of nitrogen-vacancy and silicon-vacancy centres present for the precursor material disappear. Two new characteristic features appear: (1) paramagnetic substitutional nitrogen (P1 centres with spin ½) with an electron paramagnetic resonance characteristic triplet hyperfine structure due to the I = 1 magnetic moment of the nitrogen nuclear spin and (2) the green spectral photoluminescence signature of the nitrogen-vacancy-nitrogen centres. This production method is a strong alternative to conventional high-energy particle beam irradiation. It can be used to easily produce purely green fluorescing nanodiamonds with advantageous properties for optical biolabelling applications.

scholarly journals Photoreactivity of Hair Melanin from Different Skin Phototypes—Contribution of Melanin Subunits to the Pigments Photoreactive Properties

2021 ◽  
Vol 22 (9) ◽  
pp. 4465
Author(s):  
Krystian Mokrzynski ◽  
Shosuke Ito ◽  
Kazumasa Wakamatsu ◽  
Theodore G. Camenish ◽  
Tadeusz Sarna ◽  
...  
Keyword(s):  
Chemical Composition ◽  
Singlet Oxygen ◽  
Near Infrared ◽  
Paramagnetic Resonance ◽  
Time Resolved ◽  
W Band ◽  
Epr Oximetry ◽  
X Band ◽  
Hair Samples ◽  
Electron Paramagnetic

Photoreactivity of melanin has become a major focus of research due to the postulated involvement of the pigment in UVA-induced melanoma. However, most of the hitherto studies were carried out using synthetic melanin models. Thus, photoreactivity of natural melanins is yet to be systematically analyzed. Here, we examined the photoreactive properties of natural melanins isolated from hair samples obtained from donors of different skin phototypes (I, II, III, and V). X-band and W-band electron paramagnetic resonance (EPR) spectroscopy was used to examine the paramagnetic properties of the pigments. Alkaline hydrogen peroxide degradation and hydroiodic acid hydrolysis were used to determine the chemical composition of the melanins. EPR oximetry and spin trapping were used to examine the oxygen photoconsumption and photo-induced formation of superoxide anion, and time-resolved near infrared phosphorescence was employed to determine the singlet oxygen photogeneration by the melanins. The efficiency of superoxide and singlet oxygen photogeneration was related to the chemical composition of the studied melanins. Melanins from blond and chestnut hair (phototypes II and III) exhibited highest photoreactivity of all examined pigments. Moreover, melanins of these phototypes showed highest quantum efficiency of singlet oxygen photogeneration at 332 nm and 365 nm supporting the postulate of the pigment contribution in UVA-induced melanoma.

scholarly journals Ultrafast dynamical Lifshitz transition

2021 ◽  
Vol 7 (17) ◽  
pp. eabd9275
Author(s):  
Samuel Beaulieu ◽  
Shuo Dong ◽  
Nicolas Tancogne-Dejean ◽  
Maciej Dendzik ◽  
Tommaso Pincelli ◽  
...  
Keyword(s):  
Fermi Surface ◽  
Colossal Magnetoresistance ◽  
Surface Topology ◽  
Strongly Correlated ◽  
Many Body ◽  
Time Resolved ◽  
Weyl Semimetal ◽  
Lifshitz Transition ◽  
Fermi Surface Topology ◽  
Many Body Systems

Fermi surface is at the heart of our understanding of metals and strongly correlated many-body systems. An abrupt change in the Fermi surface topology, also called Lifshitz transition, can lead to the emergence of fascinating phenomena like colossal magnetoresistance and superconductivity. While Lifshitz transitions have been demonstrated for a broad range of materials by equilibrium tuning of macroscopic parameters such as strain, doping, pressure, and temperature, a nonequilibrium dynamical route toward ultrafast modification of the Fermi surface topology has not been experimentally demonstrated. Combining time-resolved multidimensional photoemission spectroscopy with state-of-the-art TDDFT+U simulations, we introduce a scheme for driving an ultrafast Lifshitz transition in the correlated type-II Weyl semimetal Td-MoTe2. We demonstrate that this nonequilibrium topological electronic transition finds its microscopic origin in the dynamical modification of the effective electronic correlations. These results shed light on a previously unexplored ultrafast scheme for controlling the Fermi surface topology in correlated quantum materials.

scholarly journals Sigma-1 Receptor Promotes Mitochondrial Bioenergetics by Orchestrating ER Ca2+ Leak during Early ER Stress

Metabolites ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 422
Author(s):  
Zhanat Koshenov ◽  
Furkan E. Oflaz ◽  
Martin Hirtl ◽  
Johannes Pilic ◽  
Olaf A. Bachkoenig ◽  
...  
Keyword(s):  
Er Stress ◽  
Energy Demand ◽  
Molecular Mechanisms ◽  
High Energy ◽  
Human Neuroblastoma Cell ◽  
Mitochondrial Bioenergetics ◽  
Dependent Manner ◽  
Human Neuroblastoma ◽  
Sigma 1 Receptor ◽  
Sigma 1

The endoplasmic reticulum (ER) is a complex, multifunctional organelle of eukaryotic cells and responsible for the trafficking and processing of nearly 30% of all human proteins. Any disturbance to these processes can cause ER stress, which initiates an adaptive mechanism called unfolded protein response (UPR) to restore ER functions and homeostasis. Mitochondrial ATP production is necessary to meet the high energy demand of the UPR, while the molecular mechanisms of ER to mitochondria crosstalk under such stress conditions remain mainly enigmatic. Thus, better understanding the regulation of mitochondrial bioenergetics during ER stress is essential to combat many pathologies involving ER stress, the UPR, and mitochondria. This article investigates the role of Sigma-1 Receptor (S1R), an ER chaperone, has in enhancing mitochondrial bioenergetics during early ER stress using human neuroblastoma cell lines. Our results show that inducing ER stress with tunicamycin, a known ER stressor, greatly enhances mitochondrial bioenergetics in a time- and S1R-dependent manner. This is achieved by enhanced ER Ca2+ leak directed towards mitochondria by S1R during the early phase of ER stress. Our data point to the importance of S1R in promoting mitochondrial bioenergetics and maintaining balanced H2O2 metabolism during early ER stress.

scholarly journals The role of spin in the degradation of organic photovoltaics

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Ivan Ramirez ◽  
Alberto Privitera ◽  
Safakath Karuthedath ◽  
Anna Jungbluth ◽  
Johannes Benduhn ◽  
...  
Keyword(s):  
Transient Absorption ◽  
Bulk Heterojunction ◽  
Critical Factor ◽  
Model Systems ◽  
Transient Absorption Spectroscopy ◽  
Triplet States ◽  
Paramagnetic Resonance ◽  
Time Resolved ◽  
A Charge

AbstractStability is now a critical factor in the commercialization of organic photovoltaic (OPV) devices. Both extrinsic stability to oxygen and water and intrinsic stability to light and heat in inert conditions must be achieved. Triplet states are known to be problematic in both cases, leading to singlet oxygen production or fullerene dimerization. The latter is thought to proceed from unquenched singlet excitons that have undergone intersystem crossing (ISC). Instead, we show that in bulk heterojunction (BHJ) solar cells the photo-degradation of C60 via photo-oligomerization occurs primarily via back-hole transfer (BHT) from a charge-transfer state to a C60 excited triplet state. We demonstrate this to be the principal pathway from a combination of steady-state optoelectronic measurements, time-resolved electron paramagnetic resonance, and temperature-dependent transient absorption spectroscopy on model systems. BHT is a much more serious concern than ISC because it cannot be mitigated by improved exciton quenching, obtained for example by a finer BHJ morphology. As BHT is not specific to fullerenes, our results suggest that the role of electron and hole back transfer in the degradation of BHJs should also be carefully considered when designing stable OPV devices.

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