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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.

1,4-Dicyclooctatetraenyl-1,3-butadiyne and p-, m-, and o-di(cyclooctatetraenylethynyl)benzene (1−4, respectively) and their dipotassium salts (1 2-−4 2-) in THF-d 8 have been synthesized and studied by dynamic NMR spectroscopy. Rate constants for bond shift (k BS) in the neutral cyclooctatetraene (COT) rings of 1−4 and 1 2-−4 2- and for intramolecular charge (electron and cation) transfer (k CT) between the dianion and the neutral COT rings in 1 2-−4 2- have been determined. 13C NMR chemical shifts and AM1 π-charges as well as the values of k CT are interpreted on the basis of a stronger through-bond interaction between the COT rings in the order 1 2- ≫ 2 2- ≥ 4 2- > 3 2-. Similarly, k BS decreases in the order 1 2- ≫ 4 2- > 2 2- > 3 2- on going from 1−4 to the corresponding dianions. Analysis of the AM1 π-charge densities suggests that these differences are primarily due to a through-bond effect with an additional through-space contribution from the electric field of the dianion ring for bond shift in 4 2-.

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