Jump to main content
Jump to site search
Access to RSC content Close the message box

Continue to access RSC content when you are not at your institution. Follow our step-by-step guide.

Issue 38, 2016
Previous Article Next Article

Mechanical motion of molecular crystals induced by [4 + 4] photodimerisation

Author affiliations


The photomechanical bending of crystals of a stilbene-type compound substituted with anthracene and indanone groups, (E)-2-(9-anthrylmethylene)-1-indanone (trans-1), was investigated. When a narrow plate-like microcrystal was irradiated with ultraviolet (UV) light at 365 nm, the crystal gradually bent away from the light source and finally reached a semicircular shape after more than 10 min. A larger rod-like crystal, approximately 10 mm in length, also exhibited a slight bending motion. The cessation of UV irradiation caused the bent crystals to return very slowly to their straight form. In the crystals, the anthracene planes of two neighbouring trans-1 molecules are arranged in a head-to-tail parallel manner, with a short plane-to-plane distance of only 3.72 Å. The 1H nuclear magnetic resonance spectra of trans-1 crystals before and after UV irradiation revealed the intermolecular [4 + 4] photodimerisation of the two anthracene planes, while the trans-to-cis photoisomerisation was not significant. The UV-vis absorption spectra of the trans-1 powder crystals, obtained using a diffuse reflectance spectrophotometer, showed a gradual increase in absorbance between 200 and 500 nm with increasing UV irradiation time, reaching a maximum after 1 h. Thermal back-monomerisation was very slow in the dark, not recovering the initial spectrum even after 25 days. The fluorescence spectra at 570 nm, derived from the anthracene excimer, decreased in intensity with increasing UV irradiation time due to a decrease in the amount of anthracene chromophore via photodimerisation. In situ X-ray measurements revealed that the bending of the crystals was caused by slight elongation of the b axis of the unit cell, corresponding to the long axis of the rod-like crystals. Calculations revealed that the observed crystal elongation could be explained by an optimised head-to-tail [4 + 4] orientation of the anthracene dimer.

Graphical abstract: Mechanical motion of molecular crystals induced by [4 + 4] photodimerisation

Back to tab navigation

Supplementary files

Article information

13 Apr 2016
30 May 2016
First published
31 May 2016

CrystEngComm, 2016,18, 7305-7310
Article type

Mechanical motion of molecular crystals induced by [4 + 4] photodimerisation

H. Koshima, H. Uchimoto, T. Taniguchi, J. Nakamura, T. Asahi and T. Asahi, CrystEngComm, 2016, 18, 7305
DOI: 10.1039/C6CE00848H

Social activity

Search articles by author