586
K. Tawa et al.
allowed for the outline of island-like film. The crystal size was statistically evaluated
as 1.2 ± 0.4 μm in diameter and 6.0 ± 5.4 μm in length along the film surface at 1
h after UV exposure. The microcrystals gradually grew and the diameter of needleshaped crystals increased to 1.6 ± 0.3 μm, and the length increased to 7.6 ± 6.1
and 8.3 ± 6.2 μm after 24 and 41 h, respectively (Fig. 34.2d, e). The diameter and
the length of crystals evaluated by AFM were 1-2 and more than 5 μm, respectively,
which were consistent with the values evaluated by the optical microscopy. The rate
of crystal growth was found to be large within 1 h after UV exposure and to decrease
at 24 h after irradiation. So, the crystal growth process was measured in detail by
optical microscope within 1 h after irradiation. At initial 10 min, the nucleus of
microcrystal was already observed at a certain area. Then, they were spread to the
wide area in 30 min, and further, the microcrystals rapidly grew from 30 to 50 min.
On the other hand, the conversion to 1c was investigated in the photostationary
state of the film. The isobestic point in which molar extinction coefficient for openring, ε open , is equivalent to that for closed-ring, ε closed , was observed at λ = 365 nm in
absorption spectra [21]. The conversion of diarylethene 1 under the photostationary
state in a solution is described using quantum yield from 1o to 1c (QE OC ), QE from
1c to 1o (QE CO ), and ε for open-ring and closed-ring, as QE OC ε open /(QE OC ε open +
QE OC ε closed ). It is expected to be more than 99%, because QE OC and QE CO were
reported to be 0.37 and 0.0015, respectively [21]. However, the values of quantum
yield in the film state are known to be around two times larger than their values
in a solution [44] and inhomogeneous reaction occurs in the film. Therefore, the
conversion in the film is not calculated from this equation. The 1c area exposed to UV
under the microscope was scratched from the film with a small spatula and dissolved
in chloroform. Conversion was estimated from the ratio of absorbance (at 600 nm)
for the chloroform solution dissolving a film exposed to UV under microscope (1uv)
to that for the solution exposed to further UV (2uv) in order to convert entirely up
to 99%, i.e., A 1uv (600 nm)/A 2uv (600 nm). As a result, the conversion in the film was
evaluated as 87 ± 10%, which is smaller value compared with that in DAE solution.
An inhomogeneous light intensity may contribute to the lower conversion at the film
surface compared with that at the adsorbing face to the glass plate (bottom side),
because the irradiation light was absorbed by a film during passing through the film
[45].
34.3 Growth of Needle-Shaped Crystals in 1c Film
on the Plasmonic Chip
Al plasmonic chip was prepared from a UV-nanoimprint method and Al film coating
by rf-sputtering method. The pitch of periodic pattern and the groove depth were
480 nm and 30 nm, respectively. Film thickness of Al was around 40 nm. The
relation between crystal growth of 1c and isomerization to 1c was investigated at
the center part of the film with the Al plasmonic chip. The UV irradiation direction
K. Tawa et al.
allowed for the outline of island-like film. The crystal size was statistically evaluated
as 1.2 ± 0.4 μm in diameter and 6.0 ± 5.4 μm in length along the film surface at 1
h after UV exposure. The microcrystals gradually grew and the diameter of needleshaped crystals increased to 1.6 ± 0.3 μm, and the length increased to 7.6 ± 6.1
and 8.3 ± 6.2 μm after 24 and 41 h, respectively (Fig. 34.2d, e). The diameter and
the length of crystals evaluated by AFM were 1-2 and more than 5 μm, respectively,
which were consistent with the values evaluated by the optical microscopy. The rate
of crystal growth was found to be large within 1 h after UV exposure and to decrease
at 24 h after irradiation. So, the crystal growth process was measured in detail by
optical microscope within 1 h after irradiation. At initial 10 min, the nucleus of
microcrystal was already observed at a certain area. Then, they were spread to the
wide area in 30 min, and further, the microcrystals rapidly grew from 30 to 50 min.
On the other hand, the conversion to 1c was investigated in the photostationary
state of the film. The isobestic point in which molar extinction coefficient for openring, ε open , is equivalent to that for closed-ring, ε closed , was observed at λ = 365 nm in
absorption spectra [21]. The conversion of diarylethene 1 under the photostationary
state in a solution is described using quantum yield from 1o to 1c (QE OC ), QE from
1c to 1o (QE CO ), and ε for open-ring and closed-ring, as QE OC ε open /(QE OC ε open +
QE OC ε closed ). It is expected to be more than 99%, because QE OC and QE CO were
reported to be 0.37 and 0.0015, respectively [21]. However, the values of quantum
yield in the film state are known to be around two times larger than their values
in a solution [44] and inhomogeneous reaction occurs in the film. Therefore, the
conversion in the film is not calculated from this equation. The 1c area exposed to UV
under the microscope was scratched from the film with a small spatula and dissolved
in chloroform. Conversion was estimated from the ratio of absorbance (at 600 nm)
for the chloroform solution dissolving a film exposed to UV under microscope (1uv)
to that for the solution exposed to further UV (2uv) in order to convert entirely up
to 99%, i.e., A 1uv (600 nm)/A 2uv (600 nm). As a result, the conversion in the film was
evaluated as 87 ± 10%, which is smaller value compared with that in DAE solution.
An inhomogeneous light intensity may contribute to the lower conversion at the film
surface compared with that at the adsorbing face to the glass plate (bottom side),
because the irradiation light was absorbed by a film during passing through the film
[45].
34.3 Growth of Needle-Shaped Crystals in 1c Film
on the Plasmonic Chip
Al plasmonic chip was prepared from a UV-nanoimprint method and Al film coating
by rf-sputtering method. The pitch of periodic pattern and the groove depth were
480 nm and 30 nm, respectively. Film thickness of Al was around 40 nm. The
relation between crystal growth of 1c and isomerization to 1c was investigated at
the center part of the film with the Al plasmonic chip. The UV irradiation direction