The amide bridge in donor-acceptor systems: delocalization depends on push-pull stress

Transmission of electronic information through amide bonds may be, under appropriate conditions, effectively achieved. In this work, a family of explicitly designed donor-(amide bridge)-acceptor architectures was synthesized. NMR studies and UV-vis absorption solvatochromism support that cross-conjugation leads to measurable polarization across push-pull, amide-bridged molecules. Computational analysis of structural parameters and frontier molecular orbitals shows the contribution of an additional, dienoid amide canonical structure to intramolecular electron delocalization, as the electron donor-acceptor strength of the substituents increases. Within the context of nonlinear optics and molecular materials, computational comparison between amide-bridged molecules and those containing typical linkers shows that there is a compromise between nonlinear optical response, ease of synthesis and chemical inertness, making the systems studied herein interesting alternatives for such applications.