Dynamic Electromerism: Correlated Rotational and <i>Cross</i> -Conjugation Dynamics in DAMN (DiAminoMaleoNitrile) and DAFN (DiAminoFumaroNitrile) Derivatives

Conformational dynamics play key roles in molecular reactivity and the development of functional molecular machines. In this study, we investigate the competitive correlation between internal rotations about the C-NR₂ bonds and cross-conjugation dynamics in DAMN, DAFN, and their derivatives. Using a combination of NMR spectroscopy, crystallographic analysis, and computational studies, we demonstrate that conjugation in one of the two push-pull π-systems restricts its own C-N bond rotation while suspending conjugation and facilitating rotation in the other system, leading to synchronized rotation-conjugation oscillation. Variable Temperature (VT)-NMR spectroscopy revealed that the presence of competing cross-conjugated pathways drastically lowers the C-N rotational barriers of the amino groups compared to those of reference compounds presenting a single π-system (11-14 kcal/mol at 298 K). Density functional theory (DFT) studies yielded rotational barriers as low as ∼2 kcal/mol for tetra-methylated DAMN, with a disrotatory mechanism. The introduction of steric effects increased the rotational barriers, yielding measurable NMR values of 7-9 kcal/mol at coalescence in the bulkiest DAMN derivative. Additionally, modulation of the structural desymmetrization of the coupled push-pull systems in monoimine derivatives of DAMN allowed determination of rotational barriers within the range of those of the reference compounds. These effects agreed with the presence of cross-conjugation, which was also supported by X-ray diffraction. The findings provide insight into the structural factors governing rotational barriers in cross-conjugated systems exhibiting correlated molecular motion. Thus, DAMN and DAFN present a dynamic electromerism process where oscillation between two different cross-conjugation pathways is regulated by the C-N rotation frequency.