Two Consecutive Pathways Competing for Supramolecular Polymerization of Naphthalene-Diimide Molecules

The final outcomes of supramolecular assembly are determined by the pathways and the formation of intermediates during the assembly process. We studied pathway complexity involving two consecutive pathways in supramolecular polymerization of naphthalene-diimide (NDI) derivative molecule. Depending on preparation methods anisotropic aggregates of J-type nanorods (Agg I) or more flexible H-type nanofibers (Agg II) are obtained from the identical initial state in solution of methyl cyclohexane (MCH) or MCH/CHCl₃ mixtures. More interestingly intermediate aggregates driven by intra-molecular hydrogen-bonds are observed by spectroscopy and imaging techniques for both pathways. Thermodynamic model-fitting suggests that both pathways are consecutive ones with intermediate aggregates. Combining density functional theory (DFT) calculation results, we propose the molecular packing of Agg I and II. Our results reveal comprehensive pathway complexity in self-assembly of molecules as simple as NDI.