Co-reporter:Hiroshi Anzai, Neeraj Kumar Joshi, Masanori Fuyuki, Akihide Wada
Journal of Photochemistry and Photobiology A: Chemistry 2017 Volume 332() pp:364-370
Publication Date(Web):1 January 2017
DOI:10.1016/j.jphotochem.2016.09.002
•Two dimensional photostationary state absorption spectrum was observed.•Multicolor Multistep photoreaction was found in photoisomerization process.•White light excitation covering the entire visible region for transient absorption.Multicolor multistep photoisomerization process of azobenzene derivative in photostationary state was observed by newly developed Fourier transform two-dimensional (2D) spectroscopic technique. The photostationary state was generated by excitation using white light covering the entire visible region, and the photoreaction was monitored by measuring photoinduced bleaching and absorption signals detected by white light probe. The wavelength participating in excitation process for the observed signal was clarified by modulation frequency marked by passing the pump white light through a scanning tandem Fabry-Pérot interferometer, and the 2D amplitude and phase spectra were obtained by Fourier transform of the obtained 2D interferogram. By using the system, we succeeded in observing the multicolor multistep process in photoisomerization of Sudan red 7B [1-(4-[Phenylazo]phenylazo)-2-ethylaminonaphthalene, SR7B] that has two azo groups and shows several configurations. It was concluded from the analysis of obtained 2D amplitude and phase spectra that at least two reaction pathways of sequential photoisomerization reactions exist in the photostationary state of SR7B under the white light irradiation. The interpretation is supported by the results of quantum chemical calculations using density functional theory.
Co-reporter:Neeraj Kumar Joshi, Masanori Fuyuki, and Akihide Wada
The Journal of Physical Chemistry B 2014 Volume 118(Issue 7) pp:1891-1899
Publication Date(Web):January 26, 2014
DOI:10.1021/jp4125205
Spectral and kinetic behavior of thermal cis-to-trans isomerization of 4-aminoazobenzene (AAB) is examined in various solvents of different polarities. In contrast to azobenzene (AB), it is found the rate of thermal isomerization of AAB is highly dependent on solvent polarity. Accelerated rates are observed in polar solvents as compared to nonpolar solvents. Moreover, a decrease in the barrier height with an increase in medium polarity is observed. Our observations suggest that inversion is the preferred pathway in cis-to-trans thermal isomerization in a nonpolar medium; however, in a polar medium, the isomerization path deviates from the inversion route and rotational behavior is incorporated. Differences in the kinetics and in mechanisms of isomerization in different media are rationalized in terms of modulation in barrier height by polarity of the medium and solute–solvent interaction. It is found that kinetics as well as the mechanism of thermal isomerization in AAB is controlled by the polarity of the medium.
Co-reporter:Masanori Fuyuki, Koichi Furuta and Akihide Wada
RSC Advances 2013 vol. 3(Issue 20) pp:7313-7320
Publication Date(Web):04 Mar 2013
DOI:10.1039/C3RA40753E
NIR-UV two-pulse correlation measurements of a cyanine dye were conducted to study its trans-to-cis photoisomerization through a multiphoton process. The signal-to-noise ratios of the correlation traces were improved by modulating only the UV pump pulse. The absorbance change of the photo-produced cis isomers was dependent on the NIR-UV interval, and the time constant of the main decay component was 0.1 ps, which was shorter than the reported values of electronic relaxation. The results indicate that the multi-step excitation via the vibrationally excited Sn state is essential for the photoisomerization. By using the vibronic relaxation of the Sn state, we succeeded in controlling the number of cis isomers produced.
Co-reporter:Koich Furuta, Masanori Fuyuki, Akihide Wada
Chemical Physics 2013 Volume 418() pp:42-46
Publication Date(Web):3 June 2013
DOI:10.1016/j.chemphys.2013.04.010
Highlights
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Photoisomerization of DTTCI preferred two-photon process in red-tail excitation.
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Photoisomerization time from the Sn state was approximately 0.5 ns.
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Two concurrent processes are involved in the two-photon excitation process.
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Intermediate state in two-step excitation shows double-exponential decay behavior.
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Relaxation of the intermediate state shows time-constants of 0.1 ps and 5 ps.
Co-reporter:Masanori Fuyuki, Koichi Furuta, Akihide Wada
Journal of Photochemistry and Photobiology A: Chemistry 2013 Volume 252() pp:152-158
Publication Date(Web):15 January 2013
DOI:10.1016/j.jphotochem.2012.12.002
In cyanine dye, new photoreaction paths involving multiphoton processes were uncovered by ultrafast transient absorption spectroscopy. In contrast to the conventional reaction path that proceeded through one-photon resonance to the S1 state by near-infrared light irradiation, the new reaction paths were found to proceed through near-infrared multiphoton excitation to higher excited states and the optical order of the electronic excitation was dependent on the type of photoproduct: a four-photon process for cis isomers and three for photodegradation. Leuco forms with saturated hydrocarbon chain seem to be formed by photodegradation. The ultraviolet pump fluence dependence of the cis isomer production was consistent with the near-infrared pump fluence dependence. Changing the near-infrared pump fluence controlled the number ratio of cis isomers to degraded molecules.Graphical abstractHighlights► Ultrafast transient absorption spectroscopy. ► Photoisomerization of ICG molecule was completed within 2 ns. ► New photoisomerization path involving near-infrared four-photon process. ► New reaction path to leuco-forms involving near-infrared three-photon process. ► Control of the number ratio of cis-isomers to leuco-forms by changing pump fluence.
Co-reporter:Masanori Fuyuki, Koichi Furuta, Akihide Wada
Chemical Physics Letters 2011 Volume 511(1–3) pp:45-50
Publication Date(Web):26 July 2011
DOI:10.1016/j.cplett.2011.05.062
Abstract
In cyanine dye, photoisomerization paths involving multiphoton processes were found by two-color two-pulse correlation of ultrafast transient absorption spectroscopy. The reaction efficiency depended on the interval between two pump pulses, UV and NIR pulses, as well as the fluence of the NIR pulse, but was little dependent on that of the UV pulse. These results indicate that the new photoisomerization paths involve the NIR multiphoton process and/or the UV one-photon process. The difference in two-pulse correlation between positive and negative time regions revealed a new reaction path that had the highest branching ratio of cis isomer to other leuco forms.
Co-reporter:Masanori Fuyuki, Koichi Furuta, Akihide Wada
Chemical Physics Letters 2010 Volume 499(1–3) pp:121-125
Publication Date(Web):20 October 2010
DOI:10.1016/j.cplett.2010.09.042
Abstract
In cyanine dye, a photo-isomerization path involving a multiphoton process was found in addition to a conventional reaction path with a one-photon process by two-pulse correlation of transient absorption and bleaching. That photo-isomerization was completed within 3 ns and its efficiency was dependent on the interval time between two pump pulses indicate that the new path involves a multiphoton process: S0 → Sn → Sm, where Sn is ∼3.1 eV and Sm is ∼4.7 eV higher than S0 and the lifetime of intermediate state in Sn is approximately 0.2 ps. Changing the pump power controlled the branching ratio between the two paths.
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