1 Advanced Control of Photochemical Reactions …
17
observed under the one-photon excitation in the visible region [18]. In the subpicosecond time region, this absorption disappeared and the rise of absorption bands
was observed in the whole spectral region. The spectral shape of the resultant absorption band is similar to that obtained by the visible one-photon excitation although it
is broader due to larger excess vibrational energy in the 2A state [18]. These bands
decrease in a few tens of ps. At 100 ps following the excitation, almost all signal
disappeared and little bleaching signal remained, of which the result is consistent
with the small one-photon cycloreversion reaction yield of ca. 2% under the 365-nm
excitation.
On the other hand, spectral band shapes by the 730-nm off-resonant two-photon
excitation are largely different from those by the 365-nm one-photon excitation.
Although the signals around the time origin are affected by the coherent artifact
ascribable to the response of the solvent, the spectrum at 200 fs shows absorption
bands in 650–800 nm which is different from that by the 365-nm excitation. This
result indicates that the excited state (S n ’ state) pumped by the two-photon excitation
at 730 nm is different from that by the one-photon absorption at 365 nm. The absorption band in 800–900 nm increases within 1 ps but the band shape in 650–900 nm is
still different from that observed by the 365-nm excitation. This result indicates that
the S n ’ state is relaxed, at least in part, into the low excited state different from the
2A state. These positive absorption bands decrease into the baseline within several
tens of picoseconds, and the permanent bleaching markedly remains at and after at
100 ps following the excitation. The cycloreversion reaction yield was estimated to
be ca. 20% under the off-resonant two-photon excitation at 730 nm, which is 10 times
larger than that by the one-photon excitation. By integrating the large reaction yield
with the time evolution of the transient absorption spectra, it is strongly suggested
that the enhancement of the cycloreversion occurs via some specific channels leading
to the open-ring isomer without passing through the S 1 /S 0 conical intersection of the
low excited state produced by the one-photon absorption.
1.3 One-Color Control of Cyclization and Cycloreversion
Reactions of Fluorescent Diarylethenes Under CW
Visible Light Irradiation and Its Application to Ultra
Longtime Single-Molecule Tracking
In this section, we introduce the one-color control of cyclization and cycloreversion reactions of fluorescent diarylethenes. Although this control uses only single
color laser, the synergetic interaction between the material and the light leads to the
excellent performance in the super-resolution imaging.
Super-resolution optical microscopy [23–25] is a powerful tool for the investigation of the structure of small materials and for the detection of the dynamic motion
of the single fluorescent molecule with the spatial resolution beyond the diffraction
limit. Single-molecule tracking (SMT) is one of the methods for the detection of the
17
observed under the one-photon excitation in the visible region [18]. In the subpicosecond time region, this absorption disappeared and the rise of absorption bands
was observed in the whole spectral region. The spectral shape of the resultant absorption band is similar to that obtained by the visible one-photon excitation although it
is broader due to larger excess vibrational energy in the 2A state [18]. These bands
decrease in a few tens of ps. At 100 ps following the excitation, almost all signal
disappeared and little bleaching signal remained, of which the result is consistent
with the small one-photon cycloreversion reaction yield of ca. 2% under the 365-nm
excitation.
On the other hand, spectral band shapes by the 730-nm off-resonant two-photon
excitation are largely different from those by the 365-nm one-photon excitation.
Although the signals around the time origin are affected by the coherent artifact
ascribable to the response of the solvent, the spectrum at 200 fs shows absorption
bands in 650–800 nm which is different from that by the 365-nm excitation. This
result indicates that the excited state (S n ’ state) pumped by the two-photon excitation
at 730 nm is different from that by the one-photon absorption at 365 nm. The absorption band in 800–900 nm increases within 1 ps but the band shape in 650–900 nm is
still different from that observed by the 365-nm excitation. This result indicates that
the S n ’ state is relaxed, at least in part, into the low excited state different from the
2A state. These positive absorption bands decrease into the baseline within several
tens of picoseconds, and the permanent bleaching markedly remains at and after at
100 ps following the excitation. The cycloreversion reaction yield was estimated to
be ca. 20% under the off-resonant two-photon excitation at 730 nm, which is 10 times
larger than that by the one-photon excitation. By integrating the large reaction yield
with the time evolution of the transient absorption spectra, it is strongly suggested
that the enhancement of the cycloreversion occurs via some specific channels leading
to the open-ring isomer without passing through the S 1 /S 0 conical intersection of the
low excited state produced by the one-photon absorption.
1.3 One-Color Control of Cyclization and Cycloreversion
Reactions of Fluorescent Diarylethenes Under CW
Visible Light Irradiation and Its Application to Ultra
Longtime Single-Molecule Tracking
In this section, we introduce the one-color control of cyclization and cycloreversion reactions of fluorescent diarylethenes. Although this control uses only single
color laser, the synergetic interaction between the material and the light leads to the
excellent performance in the super-resolution imaging.
Super-resolution optical microscopy [23–25] is a powerful tool for the investigation of the structure of small materials and for the detection of the dynamic motion
of the single fluorescent molecule with the spatial resolution beyond the diffraction
limit. Single-molecule tracking (SMT) is one of the methods for the detection of the