The Tetracyanoquinodimethane Motif in Overcrowded Bistricyclic Aromatic Enes: Avoiding Thermochromism

Abstract

Abstract The overcrowded bistricyclic aromatic enes (BAEs) [10‐[10‐(dicyanomethylene)‐9(10 H )‐anthracenylidene]‐9(10 H )‐anthracenylidene]propanedinitrile ( 7 ) and [10‐[10‐oxo‐9(10 H )‐anthracenylidene]‐9(10 H )‐anthracenylidene)]propanedinitrile( 8 ) were synthesized by a condensation of bianthrone ( 2 ) with malononitrile in the presence of TiCl 4 and pyridine. The crystal and molecular structure of 7 were determined. It crystallizes in two polymorphic forms, belonging to the space groups P 2 1 / c and P 2 1 / 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. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)