Chapter 25
Photoresponsive Molecular Crystals
for Light-Driven Photoactuators
Seiya Kobatake and Daichi Kitagawa
Abstract Various types of photomechanical motion have drawn much attention
because there is a potential to create photomechanical actuators from molecularscale to macro-scale. To construct photoactuators, it is necessary to utilize a
molecular assembly with a small free volume. Photochromic compounds undergo
photoreversible isomerization between the original colorless isomer and the
photogenerated colored isomer upon alternating irradiation with UV and visible
light. Among many known photochromic compounds, diarylethenes undergo
photochromic reactions even in the crystalline phase. The present review introduces recent development in the study of photomechanical crystals including crystal
shape changes, bending velocity, dependence of the bending behavior on irradiation
wavelength, the behavior in mixed crystal, new types of photomechanical motion,
and applications. These photomechanical behaviors are based on geometrical structure changes in the crystalline phase and can be applied to macro-sized light-driven
photoactuators.
Keywords Photochromism · Diarylethene · Actuator · Photomechanical ·
Switching
25.1 Introduction
Molecules that change their molecular shape in response to heat and light have been
developed as mechanical materials in a very small region at the molecular level, as
known in the Nobel Prize in Chemistry 2016 “for the design and synthesis of molecular machines”. Such molecules are expected to be applied not only as individual
molecules but also as supramolecular structures that function by combining them.
However, the construction of mechanical materials and micromachines in the mesoscopic region (nanometer to micrometer) that is slightly larger than the molecular
size is not so easy because the movement of each molecule cannot be directly linked
S. Kobatake (B) · D. Kitagawa
Graduate School of Engineering, Osaka City University, Sugimoto,
Sumiyoshi-ku, Osaka 558-8585, Japan
e-mail: kobatake@a-chem.eng.oasaka-cu.ac.jp
© Springer Nature Singapore Pte Ltd. 2020
H. Miyasaka et al. (eds.), Photosynergetic Responses in Molecules
and Molecular Aggregates, https://doi.org/10.1007/978-981-15-5451-3_25
427
Photoresponsive Molecular Crystals
for Light-Driven Photoactuators
Seiya Kobatake and Daichi Kitagawa
Abstract Various types of photomechanical motion have drawn much attention
because there is a potential to create photomechanical actuators from molecularscale to macro-scale. To construct photoactuators, it is necessary to utilize a
molecular assembly with a small free volume. Photochromic compounds undergo
photoreversible isomerization between the original colorless isomer and the
photogenerated colored isomer upon alternating irradiation with UV and visible
light. Among many known photochromic compounds, diarylethenes undergo
photochromic reactions even in the crystalline phase. The present review introduces recent development in the study of photomechanical crystals including crystal
shape changes, bending velocity, dependence of the bending behavior on irradiation
wavelength, the behavior in mixed crystal, new types of photomechanical motion,
and applications. These photomechanical behaviors are based on geometrical structure changes in the crystalline phase and can be applied to macro-sized light-driven
photoactuators.
Keywords Photochromism · Diarylethene · Actuator · Photomechanical ·
Switching
25.1 Introduction
Molecules that change their molecular shape in response to heat and light have been
developed as mechanical materials in a very small region at the molecular level, as
known in the Nobel Prize in Chemistry 2016 “for the design and synthesis of molecular machines”. Such molecules are expected to be applied not only as individual
molecules but also as supramolecular structures that function by combining them.
However, the construction of mechanical materials and micromachines in the mesoscopic region (nanometer to micrometer) that is slightly larger than the molecular
size is not so easy because the movement of each molecule cannot be directly linked
S. Kobatake (B) · D. Kitagawa
Graduate School of Engineering, Osaka City University, Sugimoto,
Sumiyoshi-ku, Osaka 558-8585, Japan
e-mail: kobatake@a-chem.eng.oasaka-cu.ac.jp
© Springer Nature Singapore Pte Ltd. 2020
H. Miyasaka et al. (eds.), Photosynergetic Responses in Molecules
and Molecular Aggregates, https://doi.org/10.1007/978-981-15-5451-3_25
427