Aggregate formation of a shape-persistent acridine macrocycle via intermolecular π–π stacking

Shape-persistent macrocycles are attractive platforms for constructing well-defined π-stacked supramolecular architectures because their rigid and extended π-surfaces promote intermolecular interactions while minimising entropic penalties. Herein, we report the synthesis and aggregation behaviour of an acetylene-bridged acridine–phenylene [2 + 2] macrocycle bearing triethylene glycol monomethyl ether (TEG) side chains. The macrocycle exhibited solvent-dependent aggregation behaviour and formed π-stacked aggregates in highly polar methanol. Concentration-dependent NMR and DOSY measurements revealed the formation of larger aggregates at higher concentrations. UV–vis and fluorescence spectroscopy showed bathochromic shifts upon aggregation, indicating electronic coupling between acridine chromophores. The aggregate exhibited spectral features intermediate between H- and J-aggregates, suggesting a slipped stacking arrangement arising from the distorted structure of the macrocycle. These results demonstrate that the combination of conformational rigidity, extended π-surfaces, and solvophobic effects enables controlled acridine aggregation with tunable photophysical properties.