Nanotechnologies / Materials
Smart device, Medical & healthcare

Novel mesoscopic photo-responses achieved by combining
photochemical reactions and radiation pressure
Department of Materials Engineering Science, Graduate School of Engineering Science
Associate Professor Syoji Ito

https://researchmap.jp/itosyoji49

Professor Hiroshi Miyasaka

https://researchmap.jp/read0076304

Nanotechnologies / Materials

Abstract
Utilizing the advantageous characteristics of laser light, suchas monochromaticity, high coherence, high output intensity, andultrashort pulse duration (fs - ps), we have been exploring new
mesoscopic photoresponse of materials by combining photochemical reaction and radiation pressure. For instance, we have 1)
demonstrated the spatio-temporal control of photopolymerizationin nanospace by radiation pressure (optical trapping) and applied
it to successful fabrication of polymeric 3D microstructures and,2) developed micro-optomechanical systems based on radiationpressure controlled by photoisomerization (photochromic) reaction.
Furthermore, we have achieved selective transportation and spatial
patterning of plasmonic nanoparticles by strong radiation pressure
due to optical resonance.

and to elucidate their mechanisms. In recent years, advances in
so-called AI have been making it possible to predict the molecularand crystal structures of materials with desired physicochemical
properties based on a wide range of correlations between thedesired properties (=functions) and various characteristics, which
seems to break out the paradigm in the material science soon.
Therefore, in the future, the exploring of new physicochemical
properties that cannot be predicted from existing knowledge dueto the little information on the correlations should be more importantin material science. Along this line, we will explore further novel
mesoscopic photo-responses with a view to developing nano-processing and micro-optomechanical devices.

▍ Background & Results
Optical micromanipulation can be attained by using radiationpressure acting on small objects as a result of the momentum
change of photons. Conventionally, the main application of theradiation pressure was the manipulation of the micrometer-sizedparticles. We have extended it to nanomaterial manipulation andachieved the control of photopolymerization reaction by the trapping of the reaction intermediates.
In the liquid phase at room temperature, the lowest limit of particle size for optical trapping is generally 10-20 nm and the application of optical trapping to the control of chemical reactions has
been regarded as a difficult task. However, we pointed out thatthe radiation pressure can efficiently act on polymer chains under
propagation even in solution at room temperature and, we demonstrated the trapping of reaction intermediates (growing chains)
under photopolymerization, leading to significant improvement in
the spatial selectivity of the polymerization reaction (Fig. 1). This
is of great significance not only for its application to 3D microfabrication, but also as a pioneering study on the control of chemical
reaction by radiation pressure in terms of fundamental science. In
addition, by utilizing the dependencies of radiation pressure on theparticle shape and size, we have succeeded in selective sortingand spatial patterning of uniform silver nanorods from silver nanocolloids containing a mixture of spherical and rod-like particles(Supplementary Figure).
Optical manipulation can also be applied to the controlled motion of micro-mechanical systems that do not require electrical wiring. From such viewpoint, we have developed a novel micro-photo-mechanical systems by combining photochromic reaction andradiation pressure. By modulating the radiation pressure (mainlythe absorption force) by the photochromic reactions, we realized
micro-reciprocating motions of particles synchronizing with thephotoreaction (Fig. 2).

Fig. 1

Fig. 2▍ Significance of the research and Future perspective
Materials science including chemistry is an academic field thataims to develop new functional substances useful to human beings

Suppl. Fig.

P a t e n tIto, Syoji; Tanaka, Yoshito; Miyasaka, Hiroshi et al. Confinement of Photopolymerization and Solidification with Radiation Pressure J. Am. Chem. Soc. 2011,
133(37), p. 14472–14475, doi: 10.1021/ja200737j
Ito, Syoji; Setoura, Kenji; Miyasaka, Hiroshi et al. Mesoscopic Motion of Optically Trapped Particle Synchronized with Photochromic Reactions ofDiarylethene Derivatives J. Phys. Chem. Lett. 2018, 9(10), p. 2659–2664, doi: 10.1021/acs.jpclett.8b00890
UR
L http://www.chem.es.osaka-u.ac.jp/laser/K e y w o r d nanotechnology, micro-optomechanodevice, nanoprocessing
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