Helicene-Blade Molecular Propellers

Molecular propellers have attracted intense interest as a fascinating class of chiral molecules, as exemplified by hexaphenylbenzene derivatives bearing peripheral point-chiral substituents. However, these molecules typically show limited chiral configuration stability, hindering applications that require stable chiroptical responses. Herein, helicenes are introduced as blades to construct molecular propellers for the first time, achieving enhanced chiral stability. A stereospecific synthesis from enantiopure aza[7]helicene (A7H) is employed to obtain a propeller-shaped A7H hexamer (HA7H), which shows a high critical temperature (Tc) of 23 °C for chiral inversion. Such a high Tc sets a new record among molecular propellers (typically from –50 to 10 °C), highlighting the advantage of helicenes as blades for acquiring configurationally stable molecular propellers.