Photoswitchable glycomacrocycles as chiral dopants for liquid crystals and fabrication of microswimmers – HELISWEETCH

The recent discovery that some photochromic glycomacrocycles could substitute for “molecular motors” in the development of photoactive cholesteric liquid crystals (CLCs) opens up a huge field of research due to the great variability of natural glycosides, the infinite potentialities of substitutions and the flexibility of the syntheses of photochromic macrocycles. Such materials are of increased interest in the field of flexible photonics (reflective screens, information storage...), but also in the field of active soft matter physics. Indeed, formulated in droplets, CLCs behave as microswimmers, reproducing elementary movements of the living. The presence of the photochromic dopant adds the sensitivity to light and the possibility to guide the trajectory of the microswimmer. Based on our expertise on glycochemistry, photophysics and liquid crystals, we propose to synthesize photo-tunable cholesteric liquid crystals involving a nematic host and innovative photoswitchable glycomacrocycles as enantiomerically pure chiral dopants combining molecular photoswitch and natural carbohydrate. Glycomacrocycles containing hemiindigo or hemithioindigo will be synthesized in a convergent strategy by employing the click chemistry to achieve the macrocyclization reaction. Indigoids are promising visible-light photochromes. The influence of the nature of the photochromic and sugar units including the substituents on the sugar hydroxyl functions, the size and the geometry of the glycomacrocycles on the chirality transfer from carbohydrate to the photochromic unit(s) and as chiral dopant will be investigated by spectroscopic measurements and rationalized by DFT and TD-DFT calculations. Thanks to the ready availability and high functionality of natural carbohydrates, different substituents will be introduced on sugar hydroxyl functions so as to improve the potency of photoswitchable glycomacrocycles as chiral dopants. Through the structure-property relationship investigation and optimization of photoswitchable glycomacrocycle structures, we intend to demonstrate that such photoswitchable glycomacrocyclic dopants will provide a dynamic control of the helical superstructures of cholesteric liquid crystals in response to light stimulus, and to induce light-driven handedness inversions in self-organized helical superstructures for reflective displays, information storage, as well as for molecular machine development, for which a chiral movement can be induced and controlled by light. With the selected photoswitchable glycomacrocycles as photoswitchable chiral dopants, we envision achieving the formation of microswimmers when incorporated into micrometric droplets of cholesteric liquid crystals, and correlate the droplets trajectories (isolated or as a flock) to the extent of the photoconversion of the dopants. Based on the development of new chiral and functional supramolecular systems with renewable and abundant natural carbohydrates, the results from Helisweetch project will afford new concepts and inspire further research topics. Indeed, beyond the field of liquid crystals, the design and development of new stimuli-responsive chiral macrocycles and molecular reversible systems can bring scientific breakthroughs in other areas such as functional intelligent materials, photo-activatable catalysis, or targeted drug delivery.