Anisotropic Dissociation of π-π Stacking and Flipping-Motion-Induced Crystal Jumping in Alkylacridones and Their Dicyanomethylene Derivatives

Abstract

Ethylacridone (1 b) and dicyanomethylenated acridones 2 a,b,d showed crystal-jumping activity upon heating. This is the first example of thermosalient behavior in a simple aromatic ketone and its derivatives. A systematic investigation of the jumping behavior of derivatives with different alkyl chains by variable-temperature X-ray crystal-structure analyses revealed the mechanism of this phenomenon. Anisotropic dissociation of π stacking in a dimer was important for inducing crystal jumping in 1 b, whereas the collective fluctuation/flipping motion of a dicyanomethylene unit induced crystal jumping in 2.

Keywords: acridones; crystal growth; molecular motion; structure-activity relationships; thermosalient effects.