The tetracyanoquinodimethane motif in overcrowded bistricyclic aromatic enes: Avoiding thermochromism

The overcrowded bistricyclicaromatic enes(BAEs)[10-[10-(dicyanomethylene)- 9(10H)-anthracenylidene]-9(10H)-anthracenylidene] propanedinitrile (7) and [10-[10-oxo-9(10H)-anthracenylidene]-9(10H)-anthracenylidene)]propanedinitrile (8) were synthesized by a condensation of bianthrone (2) with malononitrile in the presence of TiCl₄ and pyridine. The crystal and molecular structure of 7 were determined. It crystallizes in two polymorphic forms, belonging to the space groups P2₁/c and P2₁/n. DFT calculations of 7 and 8 show that the overcrowding due to introducing dicyanomethylene substituents to 10 and 10′ positions is more pronounced in the twisted conformations, decreasing their stabilities. The enthalpy differences between the anti-folded and the lowest lying twisted conformations in BAEs 7 and 8 are 61.3 and 42.3 kJ/mol, respectively. In accordance with theory, BAEs 7 and 8 do not exhibit thermochromic behavior.