Single-Crystal-to-Single-Crystal Transition in an Enantiopure [7]Helquat Salt: The First Observation of a Reversible Phase Transition in a Helicene-Like Compound

Here it is reported that crystals of an enantiopure [7]helquat salt undergo reversible thermal solid-solid phase transition at 404K. Differential scanning calorimetry (DSC), capillary electrophoresis (CE), and X-ray diffraction analysis were used to unravel the mechanistic details of this process. The single-crystal-to-single-crystal course enabled direct monitoring of the structural changes by in situ variable-temperature X-ray diffraction, thus providing the first direct evidence of a solid phase transition in a helicene-like compound. Going through a phase: The first two examples of a phase transition in a helicene compound are reported. One of the phase transitions is mechanically robust and the crystal can withstand multiple thermal cycles without deterioration (see figure).