Solvent and Temperature Effects on Dynamics and Chiroptical Properties of Propeller Chirality and Toroidal Interaction of Hexaarylbenzenes

Because
of the unique interaction of radial aromatic blades, propeller-shaped
hexaarylbenzenes (HABs) attract much research interest and find various
practical applications. By introducing a small point-chiral group
at the tip of aromatic blade(s), HAB becomes propeller-chiral to exhibit
strong Cotton effects. Because of the dynamic nature of propeller
chirality, the chiroptical properties of HAB critically responded
to minute changes in the environment. Using a series of chiral HABs
with one to six (R)-1-methylpropyloxy substituent(s)
introduced at the blade tip, we elucidated how the smallest chiral
auxiliary at the HAB periphery progressively and cooperatively boosts
the overall chiroptical properties and also how subtle changes in
temperature and solvent structure affect the propeller dynamics and
thus the chiroptical responses. The unique features of propeller-chiral
HABs further enabled us to switch on/off their circularly polarized
luminescence.