An unusual stacking transformation in liquid-crystalline columnar assemblies of clicked molecular propellers with tunable light emissions.

The columnar liquid-crystalline (LC) and fluorescence properties of three-dimensional molecular propellers based on tetraphenylethylene is reported. X-ray scattering studies reveal an unusual transition from a rectangular (Colrec ) to a hexagonal columnar (Colhex ) phase. In contrast to second-order intercolumnar transitions based on a common tilt mechanism, the transition is first order and involves an unprecedented zigzag stacking of aromatic propellers in the Colrec phase. A sudden change in emission color from sky blue to green occurs rapidly and reversibly at this transition, which is due to the planarization of the propeller mesogen.