318
S. Kobatake and T. Nakahama
in Fig. 15.16c, the open-ring form crystal (crystal 1a
) produced by the photocycloreversion exhibited green fluorescence that is a significant difference from those
of crystals 1a-α and 1a-β [69]. Although the molecular geometry and intermolecular
interactions in crystal 1a
cannot be revealed due to the lack of crystallinity after
the photocycloreversion, weaker intermolecular interactions in crystal 1a
compared
with crystals 1a-α and 1a-β may lead to the green fluorescence because the orange
and yellow fluorescence of crystals 1a-α and 1a-β is ascribed to the intermolecular π-π interactions between the phenyl rings. Therefore, the introduction of steric
substituents to the phenyl rings may modulate the intermolecular π-π interactions
to result in a dramatic change in the solid-state fluorescence properties. As shown
in Fig. 15.17a, b, inverse-type diarylethenes 18a-21a having various alkyl chains
at the p-position of phenyl rings exhibit the green fluorescence that is a similar
color to that of crystal 1a
. As expected, the molecules in crystals 18a-21a have no
π-π intermolecular interaction and only van der Waals interaction, which indicates
that the alkyl chains prevent the formation of the strong π-π interaction between
the phenyl rings to result in only slight red-shifted fluorescence [70]. Therefore, the
Erase
Heating
at 150 °C
for 30 s
Write
Erase
Heating
at 150 °C
for 30 s
Write
Partly
scratching
& heating
at 90 °C
for 3 min
Erase
Heating
at 150 °C
for 30 s
Write
Scratching
& heating
at 90 °C
for 3 min
Partly
scratching
& heating
at 90 °C
for 3 min
S
S
F
F
F
F
F
F
Me
Me
R
R
18a: R = Me
19a: R = Et
20a: R = n-Pr
21a: R = n-Bu
(a)
(b)
(c)
Crystal
Amorphous
CIE
Fluorescence Intensity / a.u.
Wavelength / nm
450
500 550
600 650
700 750
0.25
0.20
0.15
0.10
0.05
0
Φ f
R = Me
Et
n-Pr
n-Bu
Fig. 15.17 a Molecular structures of inverse-type diarylethenes 18a-21a, b fluorescence spectra
of 18a in the crystalline phase (green line) and in the amorphous phase (red line); inset shows
the fluorescence quantum yields of 18a-21a in the crystalline phase and in the amorphous phase,
and c reversible fluorescence recording of 18a by partly scratching and heating observed at room
temperature upon excitation at 365 nm. Reprinted from Ref. [70]. Copyright 2019, with permission
from Elsevier
S. Kobatake and T. Nakahama
in Fig. 15.16c, the open-ring form crystal (crystal 1a
) produced by the photocycloreversion exhibited green fluorescence that is a significant difference from those
of crystals 1a-α and 1a-β [69]. Although the molecular geometry and intermolecular
interactions in crystal 1a
cannot be revealed due to the lack of crystallinity after
the photocycloreversion, weaker intermolecular interactions in crystal 1a
compared
with crystals 1a-α and 1a-β may lead to the green fluorescence because the orange
and yellow fluorescence of crystals 1a-α and 1a-β is ascribed to the intermolecular π-π interactions between the phenyl rings. Therefore, the introduction of steric
substituents to the phenyl rings may modulate the intermolecular π-π interactions
to result in a dramatic change in the solid-state fluorescence properties. As shown
in Fig. 15.17a, b, inverse-type diarylethenes 18a-21a having various alkyl chains
at the p-position of phenyl rings exhibit the green fluorescence that is a similar
color to that of crystal 1a
. As expected, the molecules in crystals 18a-21a have no
π-π intermolecular interaction and only van der Waals interaction, which indicates
that the alkyl chains prevent the formation of the strong π-π interaction between
the phenyl rings to result in only slight red-shifted fluorescence [70]. Therefore, the
Erase
Heating
at 150 °C
for 30 s
Write
Erase
Heating
at 150 °C
for 30 s
Write
Partly
scratching
& heating
at 90 °C
for 3 min
Erase
Heating
at 150 °C
for 30 s
Write
Scratching
& heating
at 90 °C
for 3 min
Partly
scratching
& heating
at 90 °C
for 3 min
S
S
F
F
F
F
F
F
Me
Me
R
R
18a: R = Me
19a: R = Et
20a: R = n-Pr
21a: R = n-Bu
(a)
(b)
(c)
Crystal
Amorphous
CIE
Fluorescence Intensity / a.u.
Wavelength / nm
450
500 550
600 650
700 750
0.25
0.20
0.15
0.10
0.05
0
Φ f
R = Me
Et
n-Pr
n-Bu
Fig. 15.17 a Molecular structures of inverse-type diarylethenes 18a-21a, b fluorescence spectra
of 18a in the crystalline phase (green line) and in the amorphous phase (red line); inset shows
the fluorescence quantum yields of 18a-21a in the crystalline phase and in the amorphous phase,
and c reversible fluorescence recording of 18a by partly scratching and heating observed at room
temperature upon excitation at 365 nm. Reprinted from Ref. [70]. Copyright 2019, with permission
from Elsevier