Preparation, property manipulation and application of α-cyanostilbene-containing photoresponsive liquid crystal elastomers with different alkoxy tail length

Photoresponsive liquid crystal elastomers have aroused wide attention due to their unique structure and properties. Most of the reported photoresponsive liquid crystal elastomers were prepared using azobenzene as photoresponsive group. There are few kinds of photoresponsive groups that can be used to construct photoresponsive liquid crystal elastomers directly. It is of great significance to develop photoresponsive liquid crystal elastomers based on new photoresponsive group and investigate the relationship between chemical structure and its properties. Herein, we reported a series of physically cross-linked photoresponsive liquid crystal elastomers with different alkoxy tail lengths (abbreviated as LCE-PM10PVPCm, m = 4, 8, 12, 16) using alpha-cyanostilbene as photoresponsive mesogens. The phase structure of the polymers, the photo-induced deformation property and the application of the LCE-PM10PVPCm fibers were thoroughly studied. The results show that LCE-PM10PVPCm with different alkoxy tail length show smectic phase. With increasing of alkoxy tail length, the glass transition temperature decreases while the clearing point temperature generally shows an increasing trend. The uniaxially oriented LCE-PM10PVPCm fibers also show a large bending angle and fast photoresponse speed when exposed to 365 nm UV light. The maximum bending angle of LCE-PM10PVPC4 can achieve 113 degrees, and the maximum bending angle decreases with the increase of alkoxy tail length. We also discussed the mechanism of this bending behavior, which is mainly attributable to trans-cis isomerization and the photothermal effect of alpha-cyanostilbene. Besides, cis alpha-cyanostilbene possesses excellent thermal stability, which endows the photoresponsive liquid crystal elastomers with application in information encryption materials.

Automated summary

This study reported physically cross-linked photoresponsive liquid crystal elastomers with different alkoxy tail lengths and investigated their phase structure, photo-induced deformation property, and application. The results showed that the glass transition temperature decreased with increasing alkoxy tail length, while the clearing point temperature generally increased. Furthermore, the uniaxially oriented fibers exhibited large bending angles and fast photoresponse speed under UV light, with the bending angle decreasing with longer alkoxy tail length.