Cyclosiloxane-based liquid-crystalline elastomers containing fluorinated mesogens and chiral crosslinking groups

A series of chiral fluorinated liquid-crystalline elastomers (LCEs) IP-VIP are prepared by 4-cyano-3-fluorophenyl 4′-(undec-10-enoyloxy)biphenyl-4-carboxylate, isosorbide bis(4-allyloxybenzoate) and 2,4,6,8-tetramethylcyclotetrasiloxane via Pt-catalyzed hydrosilylation. The chiral crosslinking moieties increase from IP to IVP. The elastomers IP, IIP, and IIIP containing low content of chiral crosslinking moieties display S_C ^* liquid-crystalline phase, but IVP, VP, and VIP do not show S_C ^* phase except for N^* mesophase. The mesophase is testified according to typical diffractogram measured by X-ray diffraction (XRD) analysis. The layer spacings of the LCEs decrease from IP (d-spacing of 34.2 Å) to VIP (d-spacing of 31.6 Å) with increase of chiral crosslinking groups in the polymers systems. Moreover, the optical properties are performed by ultraviolet–visible–near-infrared spectrophotometry. VP and VIP containing the most chiral crosslinking moieties display maximum reflection in near infrared spectra in the measurement of optical properties, while IP, IIP, IIIP, and IVP do not show obvious maximum reflection. It is interesting that a specific reflection of circularly polarized light appears along with a changing mesophase due to high enough concentration of chiral crosslinking dopants for VP and VIP. All these results suggest that the chiral crosslinking moieties exert influence on the structures of these kinds of LCEs.