Structural Effects of C6 Substitution in 6-(4-(Dimethylamino)phenyl)fulvenes

The single-crystal X-ray structures of 6-(4-(dimethylamino)phenyl)-6-methylfulvene (2) and of two polymorphs of 6-(4-(dimethylamino)phenyl)-6-phenylfulvene (3(P21/c) and 3(Pca21)) have been determined and the structures of a series of 6-arylfulvenes (1−8) have been optimized at the HF/6-31G level. Analysis of these structures reveals how resonance and crystal lattice effects influence the degree of coplanarity between the aryl and fulvene rings. The torsional angles at the aryl−fulvene bonds are significantly larger in the optimized structures than in the X-ray structures. Natural bond orbital π charges and dipole moments calculated for the X-ray and optimized structures show that the crystalline environment enhances molecular polarization. Qualitative responses for second harmonic generation in powder samples have been observed in 2, 3(Pca21), and 5. Compounds 2 and 3(Pca21) have similar packing motifs despite packing in different space groups.