Heterocycles as supramolecular handles for crystal engineering: a case study with 7-(diethylamino)coumarin derivatives.

In this study, we present the synthesis and detailed solid-state structural characterization of a Schiff-base-bridged derivative of 7-(diethylamino)coumarin (7-DAC), a molecular block displaying repetitive aggregation modes in the solid state despite being attached to broadly different molecular frameworks. To map the supramolecular habits of this unconventional moiety, we carry out a comparative analysis of the crystal packing in a curated dataset of 50 molecules decorated with the 7-DAC group, retrieved from the literature. We uncover that self-recognition of the 7-DAC moiety has two main components: a set of directional C-H⋯O interactions between neighboring coumarins, and antiparallel dipole-dipole interactions, taking the form of distinct π-stacking modes. The pendant 7-diethylamino group is key to the behavior of 7-DAC, favoring its solubilization through its conformational flexibility in solution, while in the crystalline matrix, it acts as a structural spacer that favors π-stacking interactions. Our findings present a comprehensive analysis of the preferential arrangements of the 7-DAC fragment in various (supra)molecular scenarios, confirming that it is (i) a mobile but mostly planar group, (ii) a group prone to antiparallel aggregation, and (iii) up to 90% likely to pack π-stacking supported by hydrogen-bonding interactions. These findings enrich the palette of supramolecular motifs available for the bottom-up design of organic materials and their programmed construction.