Structural effects of C-6 substitution in 6-(4-(dimethylamino)phenyl)fulvenes

The single-crystal X-ray structures of 6-(4-(dimethylamino)phenyl)-6-methyl fulvene (2) and of two polymorphs of 6-(4-(dimethylamino)phenyl)-6-phenylfu lvene (3(P2(1)/c) and 3(Pca2(1))) have been determined and the structures o f a series of 6-arylfulvenes (1-8) have been optimized at the HF/6-31G leve l. Analysis of these structures reveals how resonance and crystal lattice e ffects influence the degree of coplanarity between the aryl and fulvene rin gs. The torsional angles at the aryl-fulvene bonds are significantly larger in the optimized structures than in the X-ray structures. Natural bond orb ital pi charges and dipole moments calculated for the X-ray and optimized s tructures show that the crystalline environment enhances molecular polariza tion. Qualitative responses for second harmonic generation in powder sample s have been observed in 2, 3(Pca2(1)), and 5. Compounds 2 and 3(Pca2(1)) ha ve similar packing motifs despite packing in different space groups.