Sterically Frustrated Aromatic Enes with Various Colors Originating from Multiple Folded and Twisted Conformations in Crystal Polymorphs

Overcrowded ethylenes composed of 10-methyleneanthrone and two bulky aromatic rings contain a twisted carbon-carbon double (C=C) bond as well as a folded anthrone unit. As such, they are unique frustrated aromatic enes (FAEs). Various colored crystals of these FAEs, obtained in different solvents, correspond to multiple metastable conformations of the FAEs with various twist and fold angles of the C=C bond, as well as various dihedral angles of attached aryl units with respect to the C=C bond. The relationships between color and these parameters associated with conformational features around the C=C bond were elucidated in experimental and computational studies. Owing to the fact that they are separated by small energy barriers, the variously colored conformations in the FAE crystal change in response to various external stimuli, such as mechanical grinding, hydrostatic pressure and thermal heating.

Automated summary

This article investigates the characteristics of overcrowded ethylenes composed of 10-methyleneanthrone and two bulky aromatic rings. The crystals of these ethylenes exhibit various colors in different solvents due to their unique conformational features. Experimental studies reveal the relationships between the colors and the twist angles, fold angles, and dihedral angles of the ethylenes. Moreover, these conformations can be influenced by mechanical, pressure, and thermal stimuli.