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K. Uchida et al.
24.1 Introduction
Diarylethenes are well-known photochromic compounds which undergo cyclization
reaction to form colored closed-ring isomer upon UV irradiation, while they revert
to the original colorless open-ring isomer upon visible-light irradiation. The most
striking features of the photochromic reactions are thermal stability of both isomers,
high quantum yields of the reaction, high fatigue resistance, and photoreactivity
in the crystalline state [1, 2]. We have found the photoinduced crystal growth of
needle-shaped crystals of a closed-ring isomer upon UV irradiation to single crystal
and microcrystalline surface of a diarylethene followed by storage at 30 °C for
24 h in the dark [3]. Such photoinduced topographical changes on the surface are
due to self-aggregation of photogenerated molecules of the closed-ring isomer. The
photoinduced crystal growth technique is considered to be one of the molecular
assembling techniques.
On the other hand, photoinduced bending of a diarylethene crystals reported by
Irie et al. is also the system in which microscopic molecular photoreaction induces
the macroscopic changes of the system [4]. We aimed to build up the system where
bending crystals are aligned just like crystalline brush and they bend by photoirradiation to transport an object on the system. In the present chapter, we describe the
molecular assembled crystalline system in which photoinduced molecular change
introduced the macroscopic functional changes of the system including surface
topographical changes above mentioned.
24.2 Photoinduced Topographical Changes
of Diarylethene Derivatives Providing Control
of the Superhydrophobicity
In 2006, we have reported photoinduced topographical changes of a photochromic
diarylethene crystalline thin film of 1,2-bis(2-methoxy-5-trimethylsilylthien-3yl)perfluorocyclopentene (1o) via eutectic mixture state as shown in Fig. 24.1. Upon
UV irradiation (254 nm) to the surface of a single crystal of 1o (Fig. 24.1b), the color
became deep blue within 5 min. After 10 min irradiation with the light followed by
storage in the dark, the surface of the crystal was covered with needle-shaped crystals of 1c (Fig. 24.1c) [3, 5]. Upon irradiation of the surface with visible light (λ
> 500 nm), the color disappeared, and the needle-shaped crystals melted. Changes
in surface topography of microcrystalline film prepared by coating the chloroform
solution of 1o on a glass substrate were also found [3, 5, 6]. The explanation of the
mechanism of crystal growth and melting of the needle-shaped crystals by alternate
irradiation with UV and visible light is given by a phase diagram (Fig. 24.1d). The
shape of the crystals of 1o and 1c is cubic and needles, respectively, in the case
of recrystallization from the solutions of these isomers. The needle-shaped crystals
of 1c tend to grow in one direction along the A-axis of the crystal [3, 5, 6]. Upon
K. Uchida et al.
24.1 Introduction
Diarylethenes are well-known photochromic compounds which undergo cyclization
reaction to form colored closed-ring isomer upon UV irradiation, while they revert
to the original colorless open-ring isomer upon visible-light irradiation. The most
striking features of the photochromic reactions are thermal stability of both isomers,
high quantum yields of the reaction, high fatigue resistance, and photoreactivity
in the crystalline state [1, 2]. We have found the photoinduced crystal growth of
needle-shaped crystals of a closed-ring isomer upon UV irradiation to single crystal
and microcrystalline surface of a diarylethene followed by storage at 30 °C for
24 h in the dark [3]. Such photoinduced topographical changes on the surface are
due to self-aggregation of photogenerated molecules of the closed-ring isomer. The
photoinduced crystal growth technique is considered to be one of the molecular
assembling techniques.
On the other hand, photoinduced bending of a diarylethene crystals reported by
Irie et al. is also the system in which microscopic molecular photoreaction induces
the macroscopic changes of the system [4]. We aimed to build up the system where
bending crystals are aligned just like crystalline brush and they bend by photoirradiation to transport an object on the system. In the present chapter, we describe the
molecular assembled crystalline system in which photoinduced molecular change
introduced the macroscopic functional changes of the system including surface
topographical changes above mentioned.
24.2 Photoinduced Topographical Changes
of Diarylethene Derivatives Providing Control
of the Superhydrophobicity
In 2006, we have reported photoinduced topographical changes of a photochromic
diarylethene crystalline thin film of 1,2-bis(2-methoxy-5-trimethylsilylthien-3yl)perfluorocyclopentene (1o) via eutectic mixture state as shown in Fig. 24.1. Upon
UV irradiation (254 nm) to the surface of a single crystal of 1o (Fig. 24.1b), the color
became deep blue within 5 min. After 10 min irradiation with the light followed by
storage in the dark, the surface of the crystal was covered with needle-shaped crystals of 1c (Fig. 24.1c) [3, 5]. Upon irradiation of the surface with visible light (λ
> 500 nm), the color disappeared, and the needle-shaped crystals melted. Changes
in surface topography of microcrystalline film prepared by coating the chloroform
solution of 1o on a glass substrate were also found [3, 5, 6]. The explanation of the
mechanism of crystal growth and melting of the needle-shaped crystals by alternate
irradiation with UV and visible light is given by a phase diagram (Fig. 24.1d). The
shape of the crystals of 1o and 1c is cubic and needles, respectively, in the case
of recrystallization from the solutions of these isomers. The needle-shaped crystals
of 1c tend to grow in one direction along the A-axis of the crystal [3, 5, 6]. Upon