Structural Monitoring of the Onset of Excited-State Aromaticity in a Liquid 
Crystal Phase

Hada, Masaki; Saito, Shohei; Tanaka, Sei'ichi; Sato, Ryuma; Masahiko, Yoshimura; Mouri, Kazuhiro; Matsuo, Kyohei; Yamaguchi, Shigehiro; Hara, Mitsuo; Hayashi, Yasuhiko; Röhricht, Fynn; Herges, Rainer; Shigeta, Yasuteru; Onda, Ken; Miller, R. J. Dwayne

doi:10.1021/jacs.7b08021

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Structural Monitoring of the Onset of Excited-State Aromaticity in a Liquid Crystal Phase

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Miller, R. J. Dwayne
Miller Group, Atomically Resolved Dynamics Department, Max Planck Institute for the Structure and Dynamics of Matter, Max Planck Society;
Departments of Chemistry and Physics, University of Toronto;

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http://pubs.acs.org/doi/full/10.1021/jacs.7b08021
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Citation

Hada, M., Saito, S., Tanaka, S., Sato, R., Masahiko, Y., Mouri, K., et al. (2017). Structural Monitoring of the Onset of Excited-State Aromaticity in a Liquid Crystal Phase. Journal of the American Chemical Society, 139(44), 15792-15800. doi:10.1021/jacs.7b08021.

Cite as: https://hdl.handle.net/11858/00-001M-0000-002E-96B7-4

Abstract

Aromaticity of photoexcited molecules is an important concept in organic chemistry. Its theory, Baird’s rule for triplet aromaticity since 1972 gives the rationale of photoinduced conformational changes and photochemical reactivities of cyclic π-conjugated systems. However, it is still challenging to monitor the dynamic structural change induced by the excited-state aromaticity, particularly in condensed materials. Here we report direct structural observation of a molecular motion and a subsequent packing deformation accompanied by the excited-state aromaticity. Photoactive liquid crystal (LC) molecules featuring a π-expanded cyclooctatetraene core unit are orientationally ordered but loosely packed in a columnar LC phase, and therefore a photoinduced conformational planarization by the excited-state aromaticity has been successfully observed by time-resolved electron diffractometry and vibrational spectroscopy. The structural change took place in the vicinity of excited molecules, producing a twisted stacking structure. A nanoscale torque driven by the excited-state aromaticity can be used as the working mechanism of new photoresponsive materials.