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Issue 60, 2018, Issue in Progress
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Two-step photomechanical motion of a dibenzobarrelene crystal

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Abstract

Photomechanical crystals are interesting from both basic and applied perspectives, and thus it is important to develop new examples. We investigated the photomechanical bending behaviour of a photochromic crystal of a dibenzobarrelene derivative. When a plate-like crystal was irradiated with ultraviolet (UV) light at 365 nm, two-step bending was observed. In the first step, the crystal quickly bent away from the light source, with an accompanying crystal colour change from colourless to purple. In the second step, under prolonged UV light, the bending returned slowly and then the crystal bent up towards the opposite direction, accompanied by an additional colour change to light yellow. Spectroscopic measurements and X-ray crystallographic analysis suggested that a long-lived biradical species is generated immediately upon UV light irradiation via a Norrish type II intramolecular hydrogen abstraction, and then the final photoproducts are formed under continuous UV exposure. X-ray crystallographic analysis before and after UV light irradiation for a few seconds revealed that the longitudinal axis (a axis) of the crystal elongated slightly after irradiation, which is consistent with the direction of the first-step bending. Based on these results, we propose that first-step bending could be induced by a biradical species, generated via a Norrish type II intramolecular hydrogen abstraction, and the second-step bending could originate from the formation of a mixture of final photoproducts under prolonged light irradiation.

Graphical abstract: Two-step photomechanical motion of a dibenzobarrelene crystal

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Publication details

The article was received on 07 Aug 2018, accepted on 01 Oct 2018 and first published on 05 Oct 2018


Article type: Paper
DOI: 10.1039/C8RA06639F
RSC Adv., 2018,8, 34314-34320
  • Open access: Creative Commons BY-NC license
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    Two-step photomechanical motion of a dibenzobarrelene crystal

    T. Taniguchi, A. Kubota, T. Moritoki, T. Asahi and H. Koshima, RSC Adv., 2018, 8, 34314
    DOI: 10.1039/C8RA06639F

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