Photoswitchable liquid crystalline

Photoswitchable liquid crystalline elastomers (LCEs) for remote actuation... 

Like in other chiroptical switches (Section 5.3.1), solvent polarity was found to play an important role. Diastereoselective cyclization was observed in THF and toluene, but not in nonpolar solvents such as n-hexane. Upon photoexcitation, diarylethenes 24 (Scheme 11) can adopt a planar and a twisted conformation, and photocyclization only proceeds through the planar conformation. In the case of chiral diarylethene 27a, there are two diastereomeric planar conformations leading to the diastereomers of the cyclic product 27b. The stereoselectivity in the photocyclization process is enhanced because of a decrease in the excited state energy of the unreactive twisted form, providing a relaxation pathway for the less favorable planar diastereoisomer in more polar solvents. Chiral photochromic diarylethenes are among the most prominent photoswitches known today, featuring nondestructive read-out, excellent reversibility, and the potential for construction of switchable molecular wires and modulation of liquid crystalline phases (see Section 5.5.3).[40,411... 

Beyer P, Zentel R. 2005. Photoswitchable smectic liquid crystalline elastomers. Macromol Rapid Commun 26 874 879. 

C. Denekamp, B.L. Feringa, Optically active diarylethenes for multimode photoswitching between liquid-crystalline phases. Adv. Mater. 10, 1080-1082 (1998)... 

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