Issue 60, 2018, Issue in Progress

Two-step photomechanical motion of a dibenzobarrelene crystal

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

Supplementary files

Article information

Article type
Paper
Submitted
07 Aug 2018
Accepted
01 Oct 2018
First published
05 Oct 2018
This article is Open Access
Creative Commons BY-NC license

RSC Adv., 2018,8, 34314-34320

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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