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Yukihiro Ozaki - One of the best experts on this subject based on the ideXlab platform.
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Electronic Spectra of graphene in far and deep ultraviolet region attenuated total reflection spectroscopy and quantum chemical calculation study
Journal of Physical Chemistry C, 2018Co-Authors: Krzysztof B Bec, Yusuke Morisawa, Kenta Kobashi, Justyna Grabska, Ichiro Tanabe, Yukihiro OzakiAbstract:We measured the Electronic Spectra of graphene nanostructures (flakes and platelets) extending into the far-ultraviolet (FUV) region by attenuated total reflection far- and deep-ultraviolet (ATR–FUV–DUV) spectroscopy in the region of 2.76–8.55 eV (450–145 nm). The major absorption of graphene appears in the DUV region (4.7 eV), as already reported; however, we observed a new peak in the FUV region, visible clearly in the case of flakes at 7.5–7.7 eV (165–161 nm) and less pronounced in the spectrum of the platelets at 6.6–6.7 eV (188–185 nm). Graphene flakes (thickness 1–2 nm; sub-micrometers of side dimension) and nanoplatelets (thickness 6–8 nm; several micrometers of side dimension) give notably different ATR absorbance Spectra in the Spectral region studied. This discrepancy is reduced upon applying mechanical pressure on the samples. These observations can evidence that the morphology as well as Electronic structure of graphene can be manifested in the FUV–DUV region. Quantum chemical calculations wer...
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Electronic Spectra of graphene in far and deep ultraviolet region attenuated total reflection spectroscopy and quantum chemical calculation study
The Journal of Physical Chemistry, 2018Co-Authors: Krzysztof B Bec, Yusuke Morisawa, Kenta Kobashi, Justyna Grabska, Ichiro Tanabe, Yukihiro OzakiAbstract:We measured the Electronic Spectra of graphene nanostructures (flakes and platelets) extending into the far-ultraviolet (FUV) region by attenuated total reflection far- and deep-ultraviolet (ATR–FUV–DUV) spectroscopy in the region of 2.76–8.55 eV (450–145 nm). The major absorption of graphene appears in the DUV region (4.7 eV), as already reported; however, we observed a new peak in the FUV region, visible clearly in the case of flakes at 7.5–7.7 eV (165–161 nm) and less pronounced in the spectrum of the platelets at 6.6–6.7 eV (188–185 nm). Graphene flakes (thickness 1–2 nm; sub-micrometers of side dimension) and nanoplatelets (thickness 6–8 nm; several micrometers of side dimension) give notably different ATR absorbance Spectra in the Spectral region studied. This discrepancy is reduced upon applying mechanical pressure on the samples. These observations can evidence that the morphology as well as Electronic structure of graphene can be manifested in the FUV–DUV region. Quantum chemical calculations were applied to several molecular models incorporating the expected principal structural features of graphene nanostructures. On the basis of the results of time-dependent density functional theory and Zerner’s intermediate neglect of differential overlap (ZINDO) calculations, it was possible to consistently reproduce the experimental Spectral variations in terms of both band positions and intensities. The Spectral differences result from the differences in the die area, ordering and the number of layers, and structural factors which separate nanoflakes and nanoplatelets. These results provide insights into the probable origins of the Spectral variability of graphene nanostructures as well as the molecular orbitals involved in a FUV π–π* transition of graphene nanostructures.
Graham R Fleming - One of the best experts on this subject based on the ideXlab platform.
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room temperature coherent optical phonon in 2d Electronic Spectra of ch3nh3pbi3 perovskite as a possible cooling bottleneck
Journal of Physical Chemistry Letters, 2017Co-Authors: Daniele M Monahan, Liang Guo, Jia Lin, Letian Dou, Peidong Yang, Graham R FlemingAbstract:A hot phonon bottleneck may be responsible for slow hot carrier cooling in methylammonium lead iodide hybrid perovskite, creating the potential for more efficient hot carrier photovoltaics. In room-temperature 2D Electronic Spectra near the band edge, we observe amplitude oscillations due to a remarkably long lived 0.9 THz coherent phonon population at room temperature. This phonon (or set of phonons) is assigned to angular distortions of the Pb–I lattice, not coupled to cation rotations. The strong coupling between the Electronic transition and the 0.9 THz mode(s), together with relative isolation from other phonon modes, makes it likely to cause a phonon bottleneck. The pump frequency resolution of the 2D Spectra also enables independent observation of photoinduced absorptions and bleaches independently and confirms that features due to band gap renormalization are longer-lived than in transient absorption Spectra.
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influences of quantum mechanically mixed Electronic and vibrational pigment states in 2d Electronic Spectra of photosynthetic systems strong Electronic coupling cases
Journal of The Chinese Chemical Society, 2016Co-Authors: Yuta Fujihashi, Graham R Fleming, Akihito IshizakiAbstract:Author(s): Fujihashi, Y; Fleming, GR; Ishizaki, A | Abstract: Copyright © 2016 The Chemical Society Located in Taipei a Wiley-VCH Verlag GmbH a Co. KGaA. In 2D Electronic spectroscopy studies, long-lived quantum beats have recently been observed in photosynthetic systems, and several theoretical studies have suggested that the beats are produced by quantum mechanically mixed Electronic and vibrational states. Concerning the Electronic-vibrational quantum mixtures, the impact of protein-induced fluctuations was examined by calculating the 2D Electronic Spectra of a weakly coupled dimer with the Franck-Condon active vibrational modes in the resonant condition [Fujihashi et al., J. Chem. Phys. 2015, 142, 212403.]. This analysis demonstrated that quantum mixtures of the vibronic resonance are rather robust under the influence of the fluctuations at cryogenic temperatures, whereas the mixtures are eradicated by the fluctuations at physiological temperatures. However, this conclusion cannot be generalized because the magnitude of the coupling inducing the quantum mixtures is proportional to the inter-pigment Electronic coupling. In this study, we explore the impact of the fluctuations on Electronic-vibrational quantum mixtures in a strongly coupled dimer with an off-resonant vibrational mode. Toward this end, we calculate energy transfer dynamics and 2D Electronic Spectra of a model dimer that corresponds to the most strongly coupled bacteriochlorophyll molecules in the Fenna-Matthews-Olson complex in a numerically accurate manner. The quantum mixtures are found to be robust under the exposure of protein-induced fluctuations at cryogenic temperatures, irrespective of the resonance. At 300 K, however, the quantum mixing is disturbed more strongly by the fluctuations, and therefore, the beats in the 2D Spectra become obscure even in a strongly coupled dimer with a resonant vibrational mode. Further, the overall behaviors of the energy transfer dynamics are demonstrated to be dominated by the environment and coupling between the 0 0 vibronic transitions as long as the Huang-Rhys factor of the vibrational mode is small. The Electronic-vibrational quantum mixtures do not necessarily play a significant role in Electronic energy transfer dynamics despite contributing to the enhancement of long-lived quantum beating in the 2D Spectra.
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influence of weak vibrational Electronic couplings on 2d Electronic Spectra and inter site coherence in weakly coupled photosynthetic complexes
Journal of Chemical Physics, 2015Co-Authors: Graham R Fleming, Akihito Ishizaki, Daniele M Monahan, Lukas WhaleymaydaAbstract:Coherence oscillations measured in two-dimensional (2D) Electronic Spectra of pigment-protein complexes may have Electronic, vibrational, or mixed-character vibronic origins, which depend on the degree of Electronic-vibrational mixing. Oscillations from intrapigment vibrations can obscure the inter-site coherence lifetime of interest in elucidating the mechanisms of energy transfer in photosynthetic light-harvesting. Huang-Rhys factors (S) for low-frequency vibrations in Chlorophyll and Bacteriochlorophyll are quite small (S ≤ 0.05), so it is often assumed that these vibrations influence neither 2D Spectra nor inter-site coherence dynamics. In this work, we explore the influence of S within this range on the oscillatory signatures in simulated 2D Spectra of a pigment heterodimer. To visualize the inter-site coherence dynamics underlying the 2D Spectra, we introduce a formalism which we call the “site-probe response.” By comparing the calculated 2D Spectra with the site-probe response, we show that an on-resonance vibration with Huang-Rhys factor as small as S = 0.005 and the most strongly coupled off-resonance vibrations (S = 0.05) give rise to long-lived, purely vibrational coherences at 77 K. We moreover calculate the correlation between optical pump interactions and subsequent entanglement between sites, as measured by the concurrence. At 77 K, greater long-lived inter-site coherence and entanglement appear with increasing S. This dependence all but vanishes at physiological temperature, as environmentally induced fluctuations destroy the vibronic mixing.
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influences of quantum mechanically mixed Electronic and vibrational pigment states in 2d Electronic Spectra of photosynthetic systems strong Electronic coupling cases
arXiv: Biological Physics, 2015Co-Authors: Yuta Fujihashi, Graham R Fleming, Akihito IshizakiAbstract:In 2D Electronic spectroscopy studies, long-lived quantum beats have recently been observed in photosynthetic systems, and it has been suggested that the beats are produced by quantum mechanically mixed Electronic and vibrational states. Concerning the Electronic-vibrational quantum mixtures, the impact of protein-induced fluctuations was examined by calculating the 2D Electronic Spectra of a weakly coupled dimer with vibrational modes in the resonant condition [J. Chem. Phys. 142, 212403 (2015)]. This analysis demonstrated that quantum mixtures of the vibronic resonance are rather robust under the influence of the fluctuations at cryogenic temperatures, whereas the mixtures are eradicated by the fluctuations at physiological temperatures. However, this conclusion cannot be generalized because the magnitude of the coupling inducing the quantum mixtures is proportional to the inter-pigment coupling. In this study, we explore the impact of the fluctuations on Electronic-vibrational quantum mixtures in a strongly coupled dimer. with an off-resonant vibrational mode. Toward this end, we calculate Electronic energy transfer (EET) dynamics and 2D Electronic Spectra of a dimer that corresponds to the most strongly coupled bacteriochlorophyll molecules in the Fenna-Matthews-Olson complex in a numerically accurate manner. The quantum mixtures are found to be robust under the exposure of protein-induced fluctuations at cryogenic temperatures, irrespective of the resonance. At 300 K, however, the quantum mixing is disturbed more strongly by the fluctuations, and therefore, the beats in the 2D Spectra become obscure even in a strongly coupled dimer with a resonant vibrational mode. Further, the overall behaviors of the EET dynamics are demonstrated to be dominated by the environment and coupling between the 0-0 vibronic transitions as long as the Huang-Rhys factor of the vibrational mode is small.
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impact of environmentally induced fluctuations on quantum mechanically mixed Electronic and vibrational pigment states in photosynthetic energy transfer and 2d Electronic Spectra
arXiv: Chemical Physics, 2015Co-Authors: Yuta Fujihashi, Graham R Fleming, Akihito IshizakiAbstract:Recently, nuclear vibrational contribution signatures in 2D Electronic spectroscopy have attracted considerable interest, in particular as regards interpretation of the oscillatory transients observed in light-harvesting complexes. These transients have dephasing times that persist for much longer than theoretically predicted Electronic coherence lifetime. As a plausible explanation for this long-lived Spectral beating in 2D Electronic Spectra, quantum-mechanically mixed Electronic and vibrational states (vibronic excitons) were proposed by Christensson et al. [J. Phys. Chem. B 116, 7449 (2012)] and have since been explored. In this work, we address a dimer which produces little beating of Electronic origin in the absence of vibronic contributions, and examine the impact of protein-induced fluctuations upon Electronic-vibrational quantum mixtures by calculating the Electronic energy transfer dynamics and 2D Electronic Spectra in a numerically accurate manner. It is found that, at cryogenic temperatures, the Electronic-vibrational quantum mixtures are rather robust, even under the influence of the fluctuations and despite the small Huang-Rhys factors of the Franck-Condon active vibrational modes. This results in long-lasting beating behavior of vibrational origin in the 2D Electronic Spectra. At physiological temper- atures, however, the fluctuations eradicate the mixing and, hence, the beating in the 2D Spectra disappears. Further, it is demonstrated that such Electronic-vibrational quantum mixtures do not necessarily play a significant role in Electronic energy trans- fer dynamics, despite contributing to the enhancement of long-lived quantum beating in 2D Electronic Spectra, contrary to speculations in recent publications.
Krzysztof B Bec - One of the best experts on this subject based on the ideXlab platform.
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Electronic Spectra of graphene in far and deep ultraviolet region attenuated total reflection spectroscopy and quantum chemical calculation study
Journal of Physical Chemistry C, 2018Co-Authors: Krzysztof B Bec, Yusuke Morisawa, Kenta Kobashi, Justyna Grabska, Ichiro Tanabe, Yukihiro OzakiAbstract:We measured the Electronic Spectra of graphene nanostructures (flakes and platelets) extending into the far-ultraviolet (FUV) region by attenuated total reflection far- and deep-ultraviolet (ATR–FUV–DUV) spectroscopy in the region of 2.76–8.55 eV (450–145 nm). The major absorption of graphene appears in the DUV region (4.7 eV), as already reported; however, we observed a new peak in the FUV region, visible clearly in the case of flakes at 7.5–7.7 eV (165–161 nm) and less pronounced in the spectrum of the platelets at 6.6–6.7 eV (188–185 nm). Graphene flakes (thickness 1–2 nm; sub-micrometers of side dimension) and nanoplatelets (thickness 6–8 nm; several micrometers of side dimension) give notably different ATR absorbance Spectra in the Spectral region studied. This discrepancy is reduced upon applying mechanical pressure on the samples. These observations can evidence that the morphology as well as Electronic structure of graphene can be manifested in the FUV–DUV region. Quantum chemical calculations wer...
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Electronic Spectra of graphene in far and deep ultraviolet region attenuated total reflection spectroscopy and quantum chemical calculation study
The Journal of Physical Chemistry, 2018Co-Authors: Krzysztof B Bec, Yusuke Morisawa, Kenta Kobashi, Justyna Grabska, Ichiro Tanabe, Yukihiro OzakiAbstract:We measured the Electronic Spectra of graphene nanostructures (flakes and platelets) extending into the far-ultraviolet (FUV) region by attenuated total reflection far- and deep-ultraviolet (ATR–FUV–DUV) spectroscopy in the region of 2.76–8.55 eV (450–145 nm). The major absorption of graphene appears in the DUV region (4.7 eV), as already reported; however, we observed a new peak in the FUV region, visible clearly in the case of flakes at 7.5–7.7 eV (165–161 nm) and less pronounced in the spectrum of the platelets at 6.6–6.7 eV (188–185 nm). Graphene flakes (thickness 1–2 nm; sub-micrometers of side dimension) and nanoplatelets (thickness 6–8 nm; several micrometers of side dimension) give notably different ATR absorbance Spectra in the Spectral region studied. This discrepancy is reduced upon applying mechanical pressure on the samples. These observations can evidence that the morphology as well as Electronic structure of graphene can be manifested in the FUV–DUV region. Quantum chemical calculations were applied to several molecular models incorporating the expected principal structural features of graphene nanostructures. On the basis of the results of time-dependent density functional theory and Zerner’s intermediate neglect of differential overlap (ZINDO) calculations, it was possible to consistently reproduce the experimental Spectral variations in terms of both band positions and intensities. The Spectral differences result from the differences in the die area, ordering and the number of layers, and structural factors which separate nanoflakes and nanoplatelets. These results provide insights into the probable origins of the Spectral variability of graphene nanostructures as well as the molecular orbitals involved in a FUV π–π* transition of graphene nanostructures.
Yusuke Morisawa - One of the best experts on this subject based on the ideXlab platform.
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Electronic Spectra of graphene in far and deep ultraviolet region attenuated total reflection spectroscopy and quantum chemical calculation study
Journal of Physical Chemistry C, 2018Co-Authors: Krzysztof B Bec, Yusuke Morisawa, Kenta Kobashi, Justyna Grabska, Ichiro Tanabe, Yukihiro OzakiAbstract:We measured the Electronic Spectra of graphene nanostructures (flakes and platelets) extending into the far-ultraviolet (FUV) region by attenuated total reflection far- and deep-ultraviolet (ATR–FUV–DUV) spectroscopy in the region of 2.76–8.55 eV (450–145 nm). The major absorption of graphene appears in the DUV region (4.7 eV), as already reported; however, we observed a new peak in the FUV region, visible clearly in the case of flakes at 7.5–7.7 eV (165–161 nm) and less pronounced in the spectrum of the platelets at 6.6–6.7 eV (188–185 nm). Graphene flakes (thickness 1–2 nm; sub-micrometers of side dimension) and nanoplatelets (thickness 6–8 nm; several micrometers of side dimension) give notably different ATR absorbance Spectra in the Spectral region studied. This discrepancy is reduced upon applying mechanical pressure on the samples. These observations can evidence that the morphology as well as Electronic structure of graphene can be manifested in the FUV–DUV region. Quantum chemical calculations wer...
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Electronic Spectra of graphene in far and deep ultraviolet region attenuated total reflection spectroscopy and quantum chemical calculation study
The Journal of Physical Chemistry, 2018Co-Authors: Krzysztof B Bec, Yusuke Morisawa, Kenta Kobashi, Justyna Grabska, Ichiro Tanabe, Yukihiro OzakiAbstract:We measured the Electronic Spectra of graphene nanostructures (flakes and platelets) extending into the far-ultraviolet (FUV) region by attenuated total reflection far- and deep-ultraviolet (ATR–FUV–DUV) spectroscopy in the region of 2.76–8.55 eV (450–145 nm). The major absorption of graphene appears in the DUV region (4.7 eV), as already reported; however, we observed a new peak in the FUV region, visible clearly in the case of flakes at 7.5–7.7 eV (165–161 nm) and less pronounced in the spectrum of the platelets at 6.6–6.7 eV (188–185 nm). Graphene flakes (thickness 1–2 nm; sub-micrometers of side dimension) and nanoplatelets (thickness 6–8 nm; several micrometers of side dimension) give notably different ATR absorbance Spectra in the Spectral region studied. This discrepancy is reduced upon applying mechanical pressure on the samples. These observations can evidence that the morphology as well as Electronic structure of graphene can be manifested in the FUV–DUV region. Quantum chemical calculations were applied to several molecular models incorporating the expected principal structural features of graphene nanostructures. On the basis of the results of time-dependent density functional theory and Zerner’s intermediate neglect of differential overlap (ZINDO) calculations, it was possible to consistently reproduce the experimental Spectral variations in terms of both band positions and intensities. The Spectral differences result from the differences in the die area, ordering and the number of layers, and structural factors which separate nanoflakes and nanoplatelets. These results provide insights into the probable origins of the Spectral variability of graphene nanostructures as well as the molecular orbitals involved in a FUV π–π* transition of graphene nanostructures.
Kenta Kobashi - One of the best experts on this subject based on the ideXlab platform.
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Electronic Spectra of graphene in far and deep ultraviolet region attenuated total reflection spectroscopy and quantum chemical calculation study
Journal of Physical Chemistry C, 2018Co-Authors: Krzysztof B Bec, Yusuke Morisawa, Kenta Kobashi, Justyna Grabska, Ichiro Tanabe, Yukihiro OzakiAbstract:We measured the Electronic Spectra of graphene nanostructures (flakes and platelets) extending into the far-ultraviolet (FUV) region by attenuated total reflection far- and deep-ultraviolet (ATR–FUV–DUV) spectroscopy in the region of 2.76–8.55 eV (450–145 nm). The major absorption of graphene appears in the DUV region (4.7 eV), as already reported; however, we observed a new peak in the FUV region, visible clearly in the case of flakes at 7.5–7.7 eV (165–161 nm) and less pronounced in the spectrum of the platelets at 6.6–6.7 eV (188–185 nm). Graphene flakes (thickness 1–2 nm; sub-micrometers of side dimension) and nanoplatelets (thickness 6–8 nm; several micrometers of side dimension) give notably different ATR absorbance Spectra in the Spectral region studied. This discrepancy is reduced upon applying mechanical pressure on the samples. These observations can evidence that the morphology as well as Electronic structure of graphene can be manifested in the FUV–DUV region. Quantum chemical calculations wer...
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Electronic Spectra of graphene in far and deep ultraviolet region attenuated total reflection spectroscopy and quantum chemical calculation study
The Journal of Physical Chemistry, 2018Co-Authors: Krzysztof B Bec, Yusuke Morisawa, Kenta Kobashi, Justyna Grabska, Ichiro Tanabe, Yukihiro OzakiAbstract:We measured the Electronic Spectra of graphene nanostructures (flakes and platelets) extending into the far-ultraviolet (FUV) region by attenuated total reflection far- and deep-ultraviolet (ATR–FUV–DUV) spectroscopy in the region of 2.76–8.55 eV (450–145 nm). The major absorption of graphene appears in the DUV region (4.7 eV), as already reported; however, we observed a new peak in the FUV region, visible clearly in the case of flakes at 7.5–7.7 eV (165–161 nm) and less pronounced in the spectrum of the platelets at 6.6–6.7 eV (188–185 nm). Graphene flakes (thickness 1–2 nm; sub-micrometers of side dimension) and nanoplatelets (thickness 6–8 nm; several micrometers of side dimension) give notably different ATR absorbance Spectra in the Spectral region studied. This discrepancy is reduced upon applying mechanical pressure on the samples. These observations can evidence that the morphology as well as Electronic structure of graphene can be manifested in the FUV–DUV region. Quantum chemical calculations were applied to several molecular models incorporating the expected principal structural features of graphene nanostructures. On the basis of the results of time-dependent density functional theory and Zerner’s intermediate neglect of differential overlap (ZINDO) calculations, it was possible to consistently reproduce the experimental Spectral variations in terms of both band positions and intensities. The Spectral differences result from the differences in the die area, ordering and the number of layers, and structural factors which separate nanoflakes and nanoplatelets. These results provide insights into the probable origins of the Spectral variability of graphene nanostructures as well as the molecular orbitals involved in a FUV π–π* transition of graphene nanostructures.