Jumping Crystals of Pyrene Tweezers: Crystal-to-Crystal Transition Involving π/π-to-CH/π Assembly Mode Switching

Abstract

Crystals of pyrene tweezers 1 with interdigitating pyrenyl blades jump vigorously at around 160 °C. Single-crystal X-ray diffraction analysis before jumping revealed the presence of a "pyrene tetrad" in the crystal lattice, where four pyrenyl blades are π-stacked on top of each other. Upon heating the crystal to induce the jumping event, inner two pyrenyl blades in the "pyrene tetrad" probably rotate to switch off their π-stacking interaction with the neighboring outer pyrenyl blades and form new CH-π bonds. Different from reported salient crystals, our crystal jumps with the release of CHCl₃ as inclusion solvent.

Keywords: crystal engineering; crystal polymorphs; molecular tweezers; self-assembly; thermosalient effects.