Nature Publishing Group Acta Medica Okayama 2041-1723 10 2019 Ultrafast isomerization-induced cooperative motions to higher molecular orientation in smectic liquid-crystalline azobenzene molecules 4159 EN Masaki Hada Graduate School of Natural Science and Technology, Okayama University Daisuke Yamaguchi Department of Chemistry & Biotechnology, School of Engineering, The University of Tokyo Tadahiko Ishikawa School of Science,Tokyo Institute of Technology Takayoshi Sawa Graduate School of Natural Science and Technology, Okayama University Kenji Tsuruta Graduate School of Natural Science and Technology, Okayama University Ken Ishikawa School of Materials and Chemical Technology, Tokyo Institute of Technology Shin-Ya Koshihara School of Science,Tokyo Institute of Technology Yasuhiko Hayashi Graduate School of Natural Science and Technology, Okayama University Takashi Kato Department of Chemistry & Biotechnology, School of Engineering, The University of Tokyo The photoisomerization of molecules is widely used to control the structure of soft matter in both natural and synthetic systems. However, the structural dynamics of the molecules during isomerization and their subsequent response are difficult to elucidate due to their complex and ultrafast nature. Herein, we describe the ultrafast formation of higherorientation of liquid-crystalline (LC) azobenzene molecules via linearly polarized ultraviolet light (UV) using ultrafast time-resolved electron diffraction. The ultrafast orientation is caused by the trans-to-cis isomerization of the azobenzene molecules. Our observations are consistent with simplified molecular dynamics calculations that revealed that the molecules are aligned with the laser polarization axis by their cooperative motion after photoisomerization. This insight advances the fundamental chemistry of photoresponsive molecules in soft matter as well as their ultrafast photomechanical applications. No potential conflict of interest relevant to this article was reported.