PhD defense: Gaoyu Li

Title

Synthesis and study of photoswitchable glycosides as chiral dopants for liquid crystals

Abstract

Azobenzene-based photoswitchable glycomacrocycles combine the intrinsic chirality of sugar moiety with the reversible photoisomerization properties of azobenzene, making them promising candidates as chiral dopants for constructing photoresponsive cholesteric liquid crystals. Building upon the structural frameworks of two previously reported chiral dopants of our group, we designed and synthesized a series of nine photoswitchable glycomacrocycles along with two acyclic photoswitchable glycosides. Photophysical and photochemical investigations revealed that all synthesized compounds exhibit efficient photoisomerization, excellent fatigue resistance, and chiroptical activity for the macrocyclic compounds. Four glymacrocycles have been investigated and exhibited as chiral dopants for nematic LC hosts 5CB, DON-103, and ZLI-1132, with an amplification of helix upon E to Z photoisomerization and enforcement of helical twisting power at Z-rich state. We also demonstrated the critical influence of sugar-ring functionalization in governing chirality transfer and photoswitching behavior in cholesteric liquid crystals. Two of the synthesized glycomacrocycles uniquely achieved photoinduced helix inversion — marking the first such example for this class of compounds.

PhD supervision

• Director: Joanne Xie, Professor, PPSM, ENS Paris-Saclay
• Co-supervisor: Stéphane Maisonneuve, Research Engineer, PPSM, CNRS - ENS Paris-Saclay

Members of the jury

• Ludovic Jean, Professeur, CiTCoM, Université Paris Cité, Rapporteur

• Chrystel Lopin, Professeure, ICOA, Université d'Orléans Rapporteuse

• Stephanie Norsikian, Directrice de recherche, ICSN, CNRS, Examinatrice

• Guillaume Despras, Maître de conférences, SOFTMAT, Université de Toulouse, Examinateur