The investigation of the hydrogen bond saturation effect during the dipole―dipole induced azobenzene supramolecular self-assembly

The substituent group and hydrogen bonds play important roles in supramolecular self-assembly. To exploit the influential mechanism of hydrogen bonds during the dipole-dipole induced supramolecular self-assembly, some rigid azobenzene molecules with different electronegativity and hydrogen bonding capabilities were identified and designed. Different regular-shaped architectures were constructed via a simple solution process under mild conditions. Both experimental results and density functional theory calculations show that weak π-π stacking interactions lead to thick and short nanocylinders, strong dipole-dipole interactions and dipole induced π-π stacking lead to long and thin nanorods, appropriate hydrogen bonds consolidate the dipole-dipole interactions and dipole induced π-π stacking, forming thin nanosheets, while excessive hydrogen bonds in azobenzene would ruin the regular-shaped structures, giving irregular and stochastic aggregates. Namely there exists a certain hydrogen bond saturation effect in generating azobenzene nanostructures driven by dipole-dipole interactions. The results indicate that the morphologies of organic materials with azobenzene structures can be effectively controlled through rational molecular design by way of introducing appropriate dipole and hydrogen bonds.