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Description
The molecule 1,1'-binaphthyl is an axially chiral molecule that exists as two stable enantiomers which can change their conformation from one enantiomer to the other by overcoming a potential energy barrier of about 1 eV. Two types of crystallographic phases are known, one is racemic and the other is of chiral nature. We present an unknown type of phase which is obtained by rapid cooling from the melt with cooling rates larger than 10 °C/min. This new phase is formed also in thin films prepared by solution processing. The crystallisation process is studied by infrared thermography during melt crystallization, combined with differential scanning calorimetry and temperature-dependent in-situ X-ray powder diffraction. The new chiral phase crystallizes in the same space group $P4_12_12$ as the stable chiral phase, with slightly enlarged unit cell volume but with different molecular conformation. The new phase is unstable at room temperature and transfers into the stable chiral phase within few hours. This work demonstrates how crystallization kinetics influence the crystallization of conglomerates from a racemic melt or solution via a transient polymorphic state.