15 Solid-State Fluorescence Switching Using Photochromic …
301
transfer as described later. The fluorescence photoswitchable materials are one of the
most promising systems for ultra-high density optical memories and display devices
because the fluorescence signal can be detected even at a single-molecule level and
the change can be visually observed by naked-eye.
Although various types of the fluorescent photoswitchable systems based on the
photochromism of the diarylethene derivatives have been reported so far, most of the
researchers have focused on their fluorescence switching behaviors only in solution.
However, it is important to evaluate the fluorescence switching properties not only
in the solution but also in the solid state for practical applications such as optical
memories and display devices. Here, we have focused on the solid-state fluorescence
photoswitching behavior using the diarylethenes and reviewed the progress and the
development in this chapter. The researches on the fluorescence switching in solution are not described in detail here because many other excellent reviews reported
previously will cover the results reported so far [1, 30–34].
15.2 Ultra-High Density Optical Memory
15.2.1 Fluorescence Photoswitching at a Single-Molecule
Level
One of the advantages for fluorescence among various physicochemical properties is
that the signal can be detected even at the single-molecule level. If a single molecule
of diarylethene would work as one-bit memory, ultra-high density optical memory
(1 Pbit/inch
2 ) could be realized. In this part, various researches for the ultra-high
density optical memory are presented.
Irie and coworkers made an effort to realize the ultra-high density optical
memory based on a photochromic reaction of the diarylethenes. First, they have
tried to observe the fluorescence photoswitching at the single-molecule level using a
diarylethene–fluorophore dyad 4a that connects a fluorescent anthracene derivative
to a photochromic diarylethene via a rigid adamantyl spacer (Fig. 15.2a) [35, 36]. The
fluorescence intensity of 4a reversibly changed upon irradiation with UV and visible
light in toluene. When diarylethene is in the open-ring form, the fluorophore exhibits
fluorescence. On the other hand, when diarylethene is converted to the closed-ring
form, the fluorescence is quenched because of an energy transfer from the excitedstate fluorophore to the diarylethene closed-ring form (Fig. 15.2b). The fluorescence
photoswitching behavior at the single-molecule level was investigated using confocal
microscopy in a Zeonex polymer film doped with the closed-ring form 4b. Initially,
the polymer film was non-fluorescent. Upon irradiation with visible light, the four
fluorescent signals of 4a could be detected as shown in Fig. 15.2c. The signals disappeared by irradiation with UV light. After that, the visible light irradiation recovered
the fluorescence signals. Therefore, they accomplished that the fluorescence photoswitching can be controlled by alternating irradiation with UV and visible light at the
301
transfer as described later. The fluorescence photoswitchable materials are one of the
most promising systems for ultra-high density optical memories and display devices
because the fluorescence signal can be detected even at a single-molecule level and
the change can be visually observed by naked-eye.
Although various types of the fluorescent photoswitchable systems based on the
photochromism of the diarylethene derivatives have been reported so far, most of the
researchers have focused on their fluorescence switching behaviors only in solution.
However, it is important to evaluate the fluorescence switching properties not only
in the solution but also in the solid state for practical applications such as optical
memories and display devices. Here, we have focused on the solid-state fluorescence
photoswitching behavior using the diarylethenes and reviewed the progress and the
development in this chapter. The researches on the fluorescence switching in solution are not described in detail here because many other excellent reviews reported
previously will cover the results reported so far [1, 30–34].
15.2 Ultra-High Density Optical Memory
15.2.1 Fluorescence Photoswitching at a Single-Molecule
Level
One of the advantages for fluorescence among various physicochemical properties is
that the signal can be detected even at the single-molecule level. If a single molecule
of diarylethene would work as one-bit memory, ultra-high density optical memory
(1 Pbit/inch
2 ) could be realized. In this part, various researches for the ultra-high
density optical memory are presented.
Irie and coworkers made an effort to realize the ultra-high density optical
memory based on a photochromic reaction of the diarylethenes. First, they have
tried to observe the fluorescence photoswitching at the single-molecule level using a
diarylethene–fluorophore dyad 4a that connects a fluorescent anthracene derivative
to a photochromic diarylethene via a rigid adamantyl spacer (Fig. 15.2a) [35, 36]. The
fluorescence intensity of 4a reversibly changed upon irradiation with UV and visible
light in toluene. When diarylethene is in the open-ring form, the fluorophore exhibits
fluorescence. On the other hand, when diarylethene is converted to the closed-ring
form, the fluorescence is quenched because of an energy transfer from the excitedstate fluorophore to the diarylethene closed-ring form (Fig. 15.2b). The fluorescence
photoswitching behavior at the single-molecule level was investigated using confocal
microscopy in a Zeonex polymer film doped with the closed-ring form 4b. Initially,
the polymer film was non-fluorescent. Upon irradiation with visible light, the four
fluorescent signals of 4a could be detected as shown in Fig. 15.2c. The signals disappeared by irradiation with UV light. After that, the visible light irradiation recovered
the fluorescence signals. Therefore, they accomplished that the fluorescence photoswitching can be controlled by alternating irradiation with UV and visible light at the