Browsing by Author "Hashimoto, Sena"

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Direct observation of the change in transient molecular structure of 9,9'-bianthryl using a 10 fs pulse UV laser
(2018-08-17)
Hashimoto, Sena
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Yabushita, Atsushi
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Kobayashi, Takayoshi
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Okamura, Kotaro
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Iwakura, Izumi
Photoexcitation of 9,9'-bianthryl has been considered to produce a locally excited (LE) state and then a charge transfer (CT) state by intramolecular charge transfer (ICT) in polar solvents. In contrast, the CT state is considered to be unstable in non-polar solvents and triggers a dipole flip-flop between the two anthracene rings. The central C-C bond between the two anthracene rings is considered to twist during relaxation in the LE state and CT state, and this was visualized in the present work using an ultrashort ultraviolet (UV) pulse. The C-C stretching frequency was recovered in a period of ca. 500 fs, which implies that the C-C bond undergoes repeated torsion back and forth in the electronic excited state. Investigation of samples in a polar solvent and a non-polar solvent indicated that ICT does not affect the torsion around the central C-C bond. (C) 2018 Elsevier B.V. All rights reserved.
Real-time measurements of ultrafast electronic dynamics in the disproportionation of [TCNQ](2-)(2) using a visible sub-10 fs pulse laser
(2016-04-16)
Hashimoto, Sena
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Yabushita, Atsushi
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Kobayashi, Takayoshi
;
Iwakura, Izumi
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電子物理學系
The reduction of 7,7,8,8-tetracyanoquinodimethane (TCNQ) generates a pi radical anion, TCNQ(center dot-), that dimerizes in methanol solution. This dimer ([TCNQ](2-)(2)) exhibits a charge-transfer absorption peak at 620 nm and will disproportionate to give TCNQ and TCNQ(2-) in response to excitation within this charge transfer band. The present study examined the electronic dynamics of [TCNQ](2-)(2) disproportionation. The disproportionation was found to proceed in two steps. Electron transfer, representing the first step, occurred within the 10 fs pulse window, followed by the actual dissociation, within 350 fs. The emission lifetime of the singlet excited state of TCNQ(2-) was estimated to be 900 fs. (C) 2016 Elsevier B.V. All rights reserved.
Real-time observation of interfragment vibration and charge transfer within the TCNQF(4) dimer
(2017-08-17)
Hashimoto, Sena
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Yabushita, Atsushi
;
Iwakura, Izumi
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電子物理學系
;
Department of Electrophysics
The organic electron acceptors, 7,7,8,8-tetracyanoquinodimethane (TCNQ) and 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (TCNQF(4)); are widely used to synthesize multivalent charge-transfer complexes. Their corresponding radical anion complexes have specific electronic, optical, and magnetic characters that have attracted attention in the field of materials development. In the present work,, we have performed time-resolved absorption spectroscopy of the (Na+)(2)(TCNQE(4)(center dot-))(2) radical anion complex to elucidate the reaction dynamics ([TCNQF(4)(center dot-)](2) -> TCNQF(4) + TCNQF(4)(2-)). A visible sub-10 fs laser pulse was used to observe the ultrafast dynamics of the charge transfer and real-time change of the molecular structure during the reaction. Unlike our previous work on the (Na+)(2)(TCNQ(.-))(2) radical anion complex, the interfragment vibrational mode was clearly observed for (Na+)(2)(TCNQP(4)(center dot-))(2). The difference in the intermolecular interaction is considered to reflect the difference in the pi-pi interaction and/or the difference in the flexibility of the molecular plane predicted by theoretical calculations. (C) 2017 Elsevier B.V. All rights reserved.
Transient process spectroscopy for the direct observation of inter-molecular photo-dissociation
(2017-09-01)
Hashimoto, Sena
;
Yabushita, Atsushi
;
Iwakura, Izumi
;
電子物理學系
;
Department of Electrophysics
Transient process spectroscopy has previously been thought to be applicable only to the analysis of intra-molecular processes. Two metal ion bridges used in the present work have allowed us to visualize real-time variations of the molecular vibration frequencies during photo-disproportionation inside bimolecule aggregates, which directly shows transient inter-molecular reactions. (C) 2017 Author(s).