15 Solid-State Fluorescence Switching Using Photochromic …
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upon irradiation with UV and visible light can be undergone even in the amorphous
film; thus, the amorphous film 12a behaved as photo-patternable luminescence turnon material. They fabricated a multilayer bottom-emission type OLED using 12b
as an emissive dopant in the emitting layer, as shown in Fig. 15.11b. The fabricated device with 12b exhibited the yellow electroluminescence with an external
quantum efficiency of 0.20% (Fig. 15.11c). In addition, patterned visible light irradiation on the device is area-selectively isomerized 12b to 12a, which results in
the clear electroluminescence patterning as shown in Fig. 15.11d. The result shows
the possibility of direct photo-patterning fabrication of full-color OLEDs using the
fluorescent switchable system by the diarylethenes.
15.4 Crystalline State Fluorescence Behavior
of Diarylethenes
15.4.1 High Contrast Fluorescence Photoswitching
in Crystal
Crystals can be promising for the development of further efficient fluorescent photoswitchable materials because the molecules are regularly and very densely aggregated in the crystal. In this part, we introduce two topics, crystalline state turn-off
and turn-on mode fluorescence photoswitching with high contrast and characteristics
fluorescence behavior of inverse-type diarylethene in solid states.
As described above, 1,2-bis(3-methyl-2-thienyl)perfluorocyclopentene (9a)
exhibits turn-off mode fluorescence switching accompanying with the photochromic
reaction even in the single crystal (Fig. 15.6). However, the fluorescence on/off
contrast is not high due to the low photoconversion yield in the single crystalline
state. Fukaminato et al. designed a diarylethene derivative linked to the benzothiadiazole derivative (13a) (Fig. 15.12a) to obtain fluorescent diarylethene with efficient
turn-off mode fluorescence photoswitching properties in the single crystal [61]. Each
performance of the diarylethene and the fluorophore moieties in dyad 13a can be
carried out at a high level because they were separated by an ether bond. Initially,
the single crystal of 13a exhibited strong green fluorescence. Upon irradiation with
area-selective UV light, the fluorescence intensity of the crystal was down to the
background level. As shown in Fig. 15.12b, the size of the dark area gradually
decreased toward the center with the recovery of the fluorescence upon irradiation
with visible light. On the other hand, the fluorescence signal of quenched area in the
PMMA film containing 13a is uniformly recovered under irradiation with 438 nm
light (Fig. 15.12c). The photocyclization conversion becomes high as the position is
close to the center because UV light intensity has Gaussian distribution. The difference in the photocyclization conversion can be negligible in the PMMA film due to
the small contribution of the intermolecular energy transfer. On the other hand, the
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upon irradiation with UV and visible light can be undergone even in the amorphous
film; thus, the amorphous film 12a behaved as photo-patternable luminescence turnon material. They fabricated a multilayer bottom-emission type OLED using 12b
as an emissive dopant in the emitting layer, as shown in Fig. 15.11b. The fabricated device with 12b exhibited the yellow electroluminescence with an external
quantum efficiency of 0.20% (Fig. 15.11c). In addition, patterned visible light irradiation on the device is area-selectively isomerized 12b to 12a, which results in
the clear electroluminescence patterning as shown in Fig. 15.11d. The result shows
the possibility of direct photo-patterning fabrication of full-color OLEDs using the
fluorescent switchable system by the diarylethenes.
15.4 Crystalline State Fluorescence Behavior
of Diarylethenes
15.4.1 High Contrast Fluorescence Photoswitching
in Crystal
Crystals can be promising for the development of further efficient fluorescent photoswitchable materials because the molecules are regularly and very densely aggregated in the crystal. In this part, we introduce two topics, crystalline state turn-off
and turn-on mode fluorescence photoswitching with high contrast and characteristics
fluorescence behavior of inverse-type diarylethene in solid states.
As described above, 1,2-bis(3-methyl-2-thienyl)perfluorocyclopentene (9a)
exhibits turn-off mode fluorescence switching accompanying with the photochromic
reaction even in the single crystal (Fig. 15.6). However, the fluorescence on/off
contrast is not high due to the low photoconversion yield in the single crystalline
state. Fukaminato et al. designed a diarylethene derivative linked to the benzothiadiazole derivative (13a) (Fig. 15.12a) to obtain fluorescent diarylethene with efficient
turn-off mode fluorescence photoswitching properties in the single crystal [61]. Each
performance of the diarylethene and the fluorophore moieties in dyad 13a can be
carried out at a high level because they were separated by an ether bond. Initially,
the single crystal of 13a exhibited strong green fluorescence. Upon irradiation with
area-selective UV light, the fluorescence intensity of the crystal was down to the
background level. As shown in Fig. 15.12b, the size of the dark area gradually
decreased toward the center with the recovery of the fluorescence upon irradiation
with visible light. On the other hand, the fluorescence signal of quenched area in the
PMMA film containing 13a is uniformly recovered under irradiation with 438 nm
light (Fig. 15.12c). The photocyclization conversion becomes high as the position is
close to the center because UV light intensity has Gaussian distribution. The difference in the photocyclization conversion can be negligible in the PMMA film due to
the small contribution of the intermolecular energy transfer. On the other hand, the