The CLC phase can be generated upon the addition of a chiral dopant into an achiral nematic LC host, providing a platform for designing and creating stimuli-responsive novel materials. In 2024, the Aprahamian Group introduced a triptycene moiety, a bent-propeller-shaped aromatic, onto a photoswitchable hydrazone and demonstrated its capability to tune helical twisting power values and kinetic trapping of the helical pitch of CLCs. In order to test the versatility of triptycene as a chiral unit, Brandon and co-workers investigated the structure-property relationship of a series of triptycene-based azobenzene chiral dopants, a class of LC dopants that undergo geometric change upon photoisomerization. They found that the azobenzene-based dopants produced large helical twisting power values in the trans state and very small values in the cis state, enabling multicolored LC films. By incorporating a photomasking technique, they demonstrated the control of the trans/cis ratio at different parts of the film, resulting in structurally colored images. This work has been recently published in Angewandte Chemie.
This collaborative project with a graduate student Kai Hanke, from the University of Giessen, whose stay at Dartmouth College was supported by the Harris Program, not only led to photoswitchable CLC films that can be generated within 10 seconds, stabilized for over 24 hours, and reset with merely 60 seconds of heating, an excellent candidate material for rewritable display technology and information storage, but also a memorable friendship with lots of fun and creativity, said Brandon. Using the molecular photoswitches, they created colorful images like Van Gogh’s Starry Night or the Aprahamian lab mascot Moby.